STABILITY THEORY

For CHIEF MATES & MASTERS

TABLE OF CONTENTS :

| angle of loll | Carriage of timber | corrections tabular to assigned freeboard | critical instant dry
docking stability | damage stability | difference between type A and B | free trim wrt offshore supply
vessels | improvement of stability on ro-ro ships | inclining experiment | load line rules | loadicator |
Loadline surveys | natural rolling period | passenger vessel flooding requirement | stability of offshore
supply vessel | stability on ro-ro ships | Statical stab curve derived fm KN values | stiff tender vessels |
still water rolling period | Stress and stability data | synchronous rolling | Type A Ships loadline rules |
Type B Ships loadline rules | upthrust | virtual loss of GM | windage |

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 List stability and stress data required to be supplied to ship under the current
Load line Regulations, stating for each how such information might be used.
The load line regulations require the master of the ship is to be provided with information relating to the
stability of the ship. This usually takes the form of Stability Information Booklet which contains all that is
needed to safely manage the vessel‟s stability.

The required information is as outlined below:-

1) General Particulars
This includes the ship‟s name, official number, and port of registry, tonnage, dimensions, displacement,
deadweight, and draught to the Summer Load line. Useful as a reference in supplying information to
various official organizations such as Port Authorities, canal authorities, etc.
2) General arrangement Plan
This usually consists of a profile and plan views of the ship showing the location of all compartments,
tanks, storerooms, and accommodation. Used to locate and identify individual compartments.
3) Capacities and Centre of Gravity of cargo, fuel, water, stores, etc:
This will show the capacity and the longitudinal and vertical centre of gravity of every compartment
available for the carriage of cargo, fuel, stores, fresh water, and waterballast.
This information is required for
a) transverse stability calculations (to calculate ship‟s KG) and
b) Longitudinal Stability calculations (to calculate the ship's LCG).
Also used to calculate the space available for items of deadweight such as fuel, water, cargo, etc.
4) Estimated weight and disposition of passengers and crew:
Of particular relevance to the passenger ships. For use in transverse and longitudinal stability.
5) Estimated weight and disposition of deck cargo including 15% allowance for timber deck cargo)
For use in transverse stability calculations involving the calculation of the ship's KG and GM. Used
effectively to ensure vessel complies with the load line regulations throughout the voyage..
6) Deadweight scale
A diagram showing the load line mark and load line corresponding to the various freeboards, together with
a scale showing displacement, TPC, and deadweight for a range of draughts between Light and Load
condition.
Particularly useful when loading cargo (eg., comparing draught to estimate cargo loaded)
7) Hydrostatic particulars (Displacement, TPC, MCTC, LCB, LCF, KM)
A diagram or table showing the hydrostatic particulars of the ship such as Displacement, TPC, MCTC,
LCB, LCF, KM et.
Particularly useful for a variety of stability calculations including transverse stability and longitudinal
stability (eg., worksheets for the calculation of GM, trim and draughts forward and aft)
8) Free Surface Information (including an example)
Usually in the form of Free Surface Moments (FSM) for each tank in which liquids can be carried. The
FSM given will be for a stated relative density of the liquid (often 1.00) which will need to be adjusted if
the liquid is of another density.
Used in transverse stability calculations to find the ship's fluid KG and fluid GM.
There should also be a worked example.
9) KN tables / Cross curves (including an example)
This will take the form of a diagram or table showing the righting levers for an assumed KG (the KN is the
GZ of the vessel assuming the KG is zero). There should also be a worked example showing how a GZ
curve can be obtained using the tables/cross curves.
KN tables are used to obtain the value of GZ (as GZ = KN=-KGsinθ)
Cross curves are used to find the GZ of the vessel for any angle of heel.
10) Pre-worked Ship conditions (Lightships, Ballast Arr/Dep, Service loaded Arr/Dep,
homogenous loaded Arr/Dep, Drydocking, etc)
To include for each condition:
a) a profile diagram indicating the disposition of weights.
b) Statement of lightweight plus disposition of weight on board.
c) Metacentric height (GM)
d) The curve of statical stability (GZ curve)
e) Warning of the unsafe condition.

Very useful in cargo planning since it is easier to use a ship condition similar to
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 the proposed load condition. Also useful where the ship's tables are presented in a form unfamiliar
to the ship‟s officer who can now follow the method of calculation normally used on that vessel.
Dry dock: Enables the officer to plan the stability condition for entering the dry dock.
Loaded: Provides officer an example to establish the stability condition of the vessel
when loaded with relation to draught, trim, displacement, stress (SF & BM) and
also compliance with the loadline criteria.
Ballast: Provides officer an example to establish the stability condition of the vessel
when in ballast condition with relation to draught, trim, displacement, stress (SF &
BM) and also compliance with the loadline criteria...
Homogeneous loaded: Provides an example on cargo distribution for a given cargo to
achieve required stability criteria to enable the officer to plan for loading of various cargoes.
11) Special Procedures (Cautionary Notes)
Sometimes known as Cautionary notes. These may take the form of procedures to
maintain stability such as the partial or complete filling of spaces designated for
cargo, fuel, fresh water, etc. Examples of this are:
f) A sequence of ballasting during the voyage to maintain adequate stability, particularly to
compensate for fuel/water consumption
g) Ballasting to compensate for strong winds when carrying containers or other deck cargo.
h) Measures to compensate icing in Arctic waters
i) Any special features regarding the stowage behaviour of a particular cargo.
12) Inclining experiment report:
This will take the form of a report on the details of the inclining test showing the
calculation and other Light Ship information.
Useful in assessing the accuracy of the Lightship KG given in the stability booklet
(which may change over time)

13) Information as to Longitudinal Stresses for vessels over 150m in length

This applies to vessels over 150 mtrs in length and contains information on the
determination of the longitudinal stresses such as Shear Force, bending moment
and torsion. This will usually be in the form of comparison with maximum stress
levels for the Seagoing condition and the Harbour condition.
In this way, the ship's officer can assess the magnitude of the stresses before ,
during and after any loading, discharging or ballasting operations whether in
harbour or in a seaway.

List the surveys required by the current Loadline Regulations for a vessel to
maintain a valid Load line Certificate.
1) Initial Survey – Load line Assignment
2) Periodic Surveys:
Annual Survey –within 3 months either way of the anniversary date of the load line certificate.
The surveyor will endorse the load line certificate on satisfactory completion of the annual survey.
To be carried out every year
Renewal Survey – at an interval not exceeding 5 years

The period of validity of the load line certificate may be extended for a period not exceeding 3 months to
allow the ship to complete its voyage to the port in which it is to be surveyed.

List the items surveyed at a periodic Load line survey, describing the nature of
the survey for EACH item.
The preparation for a load line survey will involve ensuring that the hull is watertight below the freeboard
deck and weather tight above it (cargo tank lids on tankers must be watertight).

The following are checked for condition and / or weather tightness (hose test as necessary):

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 1) Superstructure/deck house weathertight doors – effective means of closure and of securing weather
tightness (dogs, clamps, hinges, weather-tight seal)
2) Hatch covers – effective means of closure and securing weather tight (cleats, clamps, wedges,
rubber sealing)
3) Side scuttles (portholes) – effective means of closure and of securing weather tight (clamps,
sealing, hinges, deadlight operation).
4) Side cargo doors – effective means of closure and of securing watertight (clamps, sealing
arrangements)
5) Other deck openings such as sounding pipe covers ullage pipe covers, tank lids, sighting ports,
manholes (deck scuttles) – effective means of closure and of securing watertight (hinges, clamps,
sealing arrangements)
6) Air pipes – permanently attached means of closure. Gauze to fuel tanks.
7) Ventilators – effective means of closure and securing weather tight (unless over a specified height).
8) Freeing ports in bulwark – free movement of flaps.
9) Scuppers, inlets, and discharges – effectiveness of non-return/storm valves.
10) Access – walkways, ladders, safety rails, bulwarks in good condition.
11) Deck fittings and appliances for timber load-lines.
12) Loadline and draught marks – measurements, correctly positioned and visibility (clarity)
13) Any changes to the hull or superstructure which may materially affect stability (eg significant
increase in Lightweight of the ship).
14) Any departure from recorded „Condition of Assignment‟ (as detailed in „Record of Particulars‟)
15) Presence of stability information Booklet and / or Loading Computer.

A vessel assigned Timer load lines is to fully load with timber on deck and in holds
in a port in a Tropical Zone, for a destination in the Winter North Atlantic zone,
during the winter months.

(a) State the minimum statutory requirements for the ship's stability throughout
the voyage.
1)
Initial GM not less than 0.05 mtrs
The maximum righting lever (GZ) at least 0.20 mtrs
Angles of Maximum GZ not be less than 30 degs
Area under the curve
0 to 30 degs not less than 0.055 mr
0 to 40 degs or θf whichever is lesser not less than 0.09 mr
Between 30 degs and 40 degs or θf not less than 0.03 mr

2) Stability calculations to assess a vessel‟s compliance with minimum stability criteria should include a
15% increase in the weight of the timber deck cargo due to water absorption.
3) Alternative KN tables taking into account for the increased freeboard due to timber deck cargo of a
specified height may be used. However such tables must assume reserve buoyancy is only 75% of the deck
timber because of the permeability of the timber deck cargo (assumed permeability 25%).

(b) Describe the various causes of any deterioration in the ship’s stability during
the voyage.
1) The vessel is loading timber in a tropical zone and most cases, the cargo will be in a dry state
condition.
2) As the vessel progresses towards the destination in the loaded passage, she proceeds to the WNA area.
3) The timber cargo may absorb more moisture which may increase the weight of more than 15%. This
reduces the GM and therefore GZ curve.
4) The free surface effect when fuel and water are consumed from the full tanks which reduced GM and
therefore GZ curve.
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 5) Consumption of fuel, stores, FW during the passage will cause G to rise thereby reducing the GM and
therefore GZ curve
6) During winter seasons, as the vessel moves towards higher latitude, will encounter a series of
depression resulting in bad weather.
7) Seas on deck will cause raise in G due to added weight and also cause FSE which reduces GM and GZ
curve
8) Whilst experiencing heavy seas, if any of the lashings gives way and cargo break loose, it can result in
catastrophic results due to deterioration of the stability of the vessel.
9) If the vessel is experiencing severe wind and spray on one side, it can result in unsymmetrical icing on
the deck and superstructure
10) As a result of this, the vessel may list or loll over to due to an increase in weight on one side.
11) This list or loss will reduce the vessel‟s stability by way
a) reduction in GM
b) produces heeling arm
c) reduction in Area under the curve or the Dynamical stability
d) Reduces the range of positive stability of the righting lever curve.
e) Reduces the maximum righting lever.
12) If the vessel is lolled over, then the situation is further worsened.
13) This is because, if the vessel is experiencing severe weather and is lolled over then wind and wave
motion will further heel the vessel.

An unstable vessel lying at an angle of loll to starboard has an empty double

bottom tank subdivided into four watertight compartments of equal width. The
tank must be ballasted to return the vessel to a safe condition.

Describe the sequence of action to be taken and the possible effects throughout
each stage.
An angle of loll is caused due to the vessel being in an unstable condition with negative GM when upright and
the vessel may heel to port or starboard.

1. Since the angle of loll is caused by G being too

high, efforts is to be directed towards
lowering it
2. As a first means of
correcting measure, one
should look towards
lowering
weight and
reducing the free
surface effect where
possible.
3. Since the vessel has D
an empty double
bottom tank B
subdivided into four watertight A
compartments of equal width following C
ballasting sequence must be carried out to return the vessel to
a safe condition:
SEQ. 1: Ballast the inner low side completely– marked A on the following figure.
SEQ. 2: Ballast the inner high side completely – marked B
SEQ. 3: Ballast the outer low side completely – marked C
SEQ. 4: Ballast the outer high side completely – marked D

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 SEQ 1:

1. The first sequence is to ballast the inner low side tank marked A.
2. While filling up the tank, due to the introduction of more free surfaces the situation will initially
worsen.
3. Moreover, an increase in the initial list will happen due to the off-center weight.
4. However as the tank starts to fill further, the G will start lowering down and the list will start to
reduce.
SEQ 2:
1. The second sequence is to fill the inner high side tank B.
2. The condition of the vessel while filling up this tank is somewhat similar to SEQ 1.
3. In this sequence, although there is free surface effect initially, the KG of the vessel will decrease as
the tank is filled up due to the concentration of weight at the lower part of the ship.
4. As the tank is finally filled, the free surface effect is eliminated and the KG will reduce even
further thereby improving the vessel‟s stability.

SEQ 3:

1. Fill up the outer low side tank marked C .

2. The purpose is to further reduce the KG and improve the stability of the vessel.
3. One of the main reasons to lower KG is to have positive GM to eliminate the angle of loll.
4. As the tank is filled up it will have free surfaces initially.
5. However, by now tank A and B are filled fully which has reduced the KG considerably.
6. Filling this tank will in effect create only starboard listing moment as the angle of loll will most
probably have been eliminated due to filling tanks A and B.

SEQ 4:
1. This will be the final sequence of ballasting which will be the outer high side tank marked D.
2. By filling up this tank the GM is further improved and the port moment produced by this tank will
offset the starboard moment produced by filling tank C.
3. The G of the vessel will be lowered sufficiently and the ship should be completely upright
condition when this tank is completely filled.

DON’Ts:
1. Do not fill the outer high side tank first because the added weight may cause the vessel to suddenly
and violently roll over to the other side with a possibility of the moment of the roll carrying the ship
over past the angle of vanishing stability and therefore capsizing the vessel.
2. This is because generally at loll the port list moments are equal to the starboard list moments and
there is no list. It is only with the case of the list it is prudent to fill the high side tank.
3. Even if the vessel does not capsize, such a sudden roll may result in injury to personnel or shift of
cargo with its implications on the ship's stability.

Describe how a vessel lying at an angle of loll may be returned to a safe condition.
An angle of loll is caused due to the vessel being in an unstable condition with negative GM when upright and
the vessel may heel to port or starboard.

1) Ensure that the heel is due to the negative GM rather than off-center weight.
2) That is to ensure that the port listing moment is equal to the starboard listing moment.
3) Since the angle of loll is caused by G being too high, an effort is to be directed towards lowering it.
a) This can be done by shifting weight onboard.
b) If the vessel has high ballast tanks then these may be emptied by discharging the ballast from
the high side tank first. Once the high side tank is emptied then empty the lower side tank.
4) One should look towards lowering the weights and reducing free surface effect where possible i.e., by
pressing up tanks.
5) Should it be necessary to fill the double bottom, it is important to choose a divided tank first to
minimize the free surface effect

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 6) One tank should be filled at a time and always fill the lower side first. This will probably cause an
initial increase in the list because of the off-center weight and generated free surface effect, but after
that, the list will start to reduce as G is lowered.
7) Where a double bottom is subdivided into three equal watertight compartments, then
a) it is logical to fill the centre tank first since the added weight will cause the G to move
vertically downwards and the heel will therefore reduce as the tank fills.
b) Neither will it cause the vessel to roll over to the high side since the added weight is not off
centre.
c) Fill the low side tank completely
d) Finally. Fill the high side tank. By the time this tank is completely full, the vessel will be in the
upright condition as the vessel's stability is improved by this time and GM being positive.
8) Where there are four athwartship tanks the order recommended is:
a) Ballast the inner low side first.
b) Ballast the inner high side completely
c) Ballast the outer low side completely
d) Ballast the outer high side completely
9) Before considering any of the above, if the vessel is at sea where the ship is lolled over then the
following shall be carefully observed.
a) Alter course to put the ship‟s head into the predominant waves.
b) The ship must stay in lolled to the same side.

Explain why the information provided by a curve of statical stability, derived from
KN values should be treated with caution
1) GZ curves are the best way of assessing a ship‟s stability but they do have limitations as they are based
upon theoretical values.
2) This is because no account is taken of what may happen in practice at a large angle of heel e.g.,
flooding through ventilators, shifting of cargo, etc.
3) The KN values are tabulated for various angles of heel for a range of displacements. These values are
derived based on the fact that it would be convenient to consider the GZ that would exist if G were at
Keel, termed KN.
4) The KG of the vessel is assumed to be zero, therefore all KN values need to be corrected to take into
account the actual KG of the vessel.
5) The GZ value is predominantly dependent upon the KG.
6) Hence to obtain the actual GZ for a given value of KG, a correction need to be made for the actual
height of G above the keel.
7) GZ = KN-KGsinθ. KN value must be interpolated between two sets of displacement to arrive at the
desired displacement. KG values dependent upon displacement and the displacement is dependant upon
the accuracy of weights onboard including the lightship displacement and KG.
8) The lightship KG and displacement are no longer the same that was calculated when the ship was
built.
9) GZ values are based upon an assumed trim condition which may not be the vessel‟s actual trim,
although some vessels have different KN tables for different trim conditions.
10) A further complication is that of Free trim where the vessel changes its trim as it heels.
11) This condition is very much obvious in the case of smaller vessels like offshore supply vessels.
Trimming by stern on such vessels will reduce the waterplane area especially when the vessel's low
stern goes into the water and the aft deck floods.
12) Reduction in the waterplane area reduces the vessel's stability and therefore the KN values for that
angle of heel.
13) Thus the GZ curve obtained using KN values of fixed trim, then the curve obtained will be incorrect
one and will tend to show that the vessel has a better stability.
14) Water shipped on deck will not be accounted for. Such water will change the vessel's KG creating free
surface moment as the vessel rolls in a seaway.
15) Also, dynamic factors such as synchronous rolling, parametric rolling, and loss of stability cannot be
appreciated by inspection of a curve of statical stability such as righting lever or righting moment
curve.

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Describe the effect of a heavy list on a vessel’s stability.
1) When a vessel is listed the G lies off the centre line to port or starboard.
2) GZ is actually a capsizing lever with a negative GZ when the vessel is upright.
3) GZ is negative till the angle of list.
4) At the angle of list GZ is zero.
5) If the ship is heels beyond the angle of list, positive GZ is produced and it is now a righting moment.
6) The maximum residual GZ is reduced. The loss of GZ due to list = GGH x Cosθ
7) As Cosθ = 1, the loss of GZ is maximum when the ship is upright.
8) The area under the curve (dynamical stability) is decreased due to losing the area under the heeling arm
curve.
9) The angle of maximum GZ value is increased by a small amount.
10) The range of stability is reduced.
11) No change in the angle of deck edge immersion but it is easily reached on the listed side when acted
upon by the external forces.
12) Since the ship is already listed, external forces can easily heel the ship to a more dangerous angle of
heel on the listed side.

(If this question forms part of a question where they have asked to show the GZ curve with list condition, only
the above answer will suffice. If asked as a stand-alone questions then curve need to be drawn)

Discuss the use, limitation, and relative accuracy of EACH of the following means
of stability assessment.
Simplified Stability tables (eg., Max KG)

Use:
(a) These are incorporated in the ship‟s stability booklet either as a diagram or a table.
(b) A quick assessment of the ship's stability as to whether or not all statutory criteria are complied with is
achieved utilizing a single diagram or table
(c) Eliminates the need to use cross curves or GZ curves for different loading conditions.
(d) Three methods of presentation are:
- Maximum deadweight moment or table
- Maximum permissible KG diagram or table.
- minimum permissible GM diagram or table.

Initial Metacentric Height (GM)

Use:
(a) Used to determine the initial stability of the vessel i.e., the stability of the vessel at small angles of heel.
(b) IMO Load Line Regulations stipulates the minimum value of Initial GM for a different type of vessel.

(c) Hence at a glance of initial GM for that type of vessel, once can ascertain the stability condition of the
vessel. However, to comply fully with the regulations, there are other aspects that need to be complied
with.

Explain the meaning of Free Trim and its particular reference to offshore supply
vessels.
Free trim is the sudden and significant moment suffered by the Offshore supply vessels after a certain angle of
heel due to the shift of LCB and LCF forward. The bow is up and the stern in trimmed down. This effect is
explained as follows:

1. Free trim effect is observed in Offshore supply vessels with high forecastle (normally forward
superstructure) and a low working after deck.
2. When the ship is heeled over to immerse the after deck line, the forecastle remains well over the
waterline.
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 3. The waterplane area aft on the low side has been lost causing the F to move forward. The ship starts to
trim by the stern.
4. As the ship progressively heels further the reserve buoyancy of the forward superstructure takes effect,
the volume of buoyancy being transferred from the high side aft where it is not being used to the low
side on the heeled side.
5. This causes the LCB to move forward.
6. This accompanied by the continuing forward movement of the LCF causes the ship to trim significantly
further by the stern as it continues to heel.
7. This situation leads to the danger of after deck being flooded.
8. The stability of the vessel is greatly reduced due to the reduction in the waterplane area and hence
reduction in the KN value.
9. If the ship's KN value has been calculated for fixed trim they will result in an incorrect GZ curve and
will tend to show that the vessel has better stability than it has at large angles of heel.
10. Fixed trim KN data will give greater GZ values than what the ship will have when heeled beyond the
angle of deck edge immersion - stability will be overestimated.
11. Therefore the KN values of the ship should be derived on a "free to trim basis and the KN tables should
have the statement "Corrected for Free trim".

A vessel with a high deck cargo will experience adverse effects due to strong beam
winds on the lateral windage areas.
Explain how the effects of steady and gusting winds can be determined and state
the minimum stability requirements concerning wind heeling under the current
regulations
1. A vessel with high deck cargo may have their stability considerably reduced when subjected to strong
beam winds.
2. A heel angle will be produced by the strong beam winds acting upon large lateral areas of the ship.
3. This lateral area may be a combination of high freeboard and tiers of containers on deck.
4. The wind heeling moments are the moments produced by this force, multiplied by a heeling lever,
tending to incline the vessel. (moments produced by wind X heeling lever)
5. The components of wind heeling moments are:
a) Wind Force (F) – Force per unit area (kgs/m2).
b) Windage area (A) – Area (m2).
c) Lever (d) – Distance of centroid of windage area from
the centroid of buoyancy (B)

6. Heeling moments = Force x distance = FAd ÷ 1000 tonnes. Metres.

7. The vessel will continue to heel until an equal and opposite force is produced i.e., righting moments of
equal value to the heeling moments, resulting in a steady angle of heel.
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 Righting moments = Wind Heeling moments
Δ x GZ = FAd
1000

8. Therefore GZ loss at an angle of heel = Heeling Moment † Δ

= FAd † 1000 x Δ

9. The GZ loss due to wind heeling produces a heeling arm

10. The wind heeling moments are usually represented by a straight horizontal line on the curve of statical
stability.
11. This is due to the presumption that the wind heeling moments do not change as the vessel heels.
12. In practice, the wind heeling moments will tend to reduce as the vessel heels due to the inclination of
the windage area reducing the heel force. However, for stability it is assumed that the wind heeling
force remains constant throughout, resulting in the horizontal heeling arm across the curve.

MINIMUM STABILITY REQUIREMENTS:

1. Applies to container ships.

2. Where the height of the lateral Windage area from the load water line to the top of the containers is
great than 30% of the beam, the regulations require that the shipbuilder produces a curve of righting
moments for the worst possible service conditions together with the total windage area, the position of
its centriod and the lever to half draught.
3. Steady wind Heeling Moment (λ) = F.A.d † 1000 (t.m.), where F = 48.5 kgs/m2.
4. The wind force is dynamic which is equal to Gusting wind ±50%.
5. Gusting wind heeling moment = Steady wind Heeling Moment (λ) x 1.5
6. Therefore Heel arm maximum = GZ loss x 1.5.
7. From the following curve, it is required that
a) Steady wind heel θ1 is not more than 65% of the Angle of deck edge immersion (θde).
b) The angle of dynamic Heel (θdy) not more than the Angle of progressive flooding (θf)
c) Area "S2' is equal to or more than Area S1 up to θf

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Concerning the modern shipboard stability and stress finding instrument:

(a) State the hydrostatic and stability data already pre-programmed into the
instrument.
1) Ship‟s dimensions and general particulars.
2) The capacity of all internal spaces.
3) VCG / LCG / FSM of all internal spaces (cargo spaces, ballast tanks fuel , FW, etc)
4) Hydrostatic particulars – Displacement, draught, TPC, MCTC, LCB, LCF, KM
5) Lightship data – Lightship displacement and KG.
6) KN data
7) Stability limits (Loadline, Grain, Timber, etc)
8) Simplified Stability Data (e.g., MAX KG)
9) Structural Stress Limits
10) Grain Loading data (as in grain loading booklet)
11) Wind Heeling Data
12) Ice Allowance Data

(b) Describe the information to be entered into the instrument by the ship’s
officer.
1) Location and weight of individual items of deadweight – cargo, fuel, ballast, stores, freshwater,
passengers, etc.
2) Loadline zone
3) R.D. of seawater/dock water
4) R.D. of liquids – fuel, ballast, liquid cargo, etc.
5) S.F. of bulk cargoes (e.g. grain)

(c) Describe the output information

1) Deadweight summary.
2) Trim and draught (forward, aft, midships, freeboard)
3) Heel
4) Stability Assessment – Gm, GZ curve, dynamical stability, etc.
5) Simplified Stability diagram and assessment.
6) Stress Assessment – Shear force, Bending moment, Torsion.
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 7) Grain loading assessment.
8) Local load assessment – e.g., container stack weight

The stress data is usually given as a percentage of the maximum allowable at that particular point along the
length of the vessel. Hence two variables are the actual stress encountered and the corresponding strength of
the vessel at that point which resists that particular stress.

State the purpose of the inclining experiment.

The purpose of performing an inclining experiment on the vessel is to determine the value of the KG in the
lightship condition. The determination of lightship KG is required because the light KG changes over a period
of time. Moreover, the lightship KG and displacement value are the basis from which the KG is determined for
every other condition. An error in the KG calculated for any condition of loading will result in inaccuracy in all
stability parameters dependant on this value – GM, GZ values, and dynamical stability.

During the experiment, the LCG for the light condition will also be determined.

Describe the precautions to be taken by the SHIP’s OFFICER before and during
the inclining experiment.
1) The ship must be moored in quiet sheltered waters free from the effects of passing vessels.
2) There must be an adequate depth of water under the keel so that the bottom of the ship does not touch
the sea bed on inclination.
3) There should little or no wind. If there is any wind the ship should be head-on or stern to it.
4) The ship should be floating free. There should be no barges alongside.
5) Moorings should be slackened right down.
6) Shore side gangway if any must be landed to allow unrestricted heeling.
7) All loose weights must be removed or secured.
8) All fittings and types of equipment such as the accommodation ladder, derricks/cranes should be
stowed in their normal seagoing positions.
9) The free surface should be minimized. All tanks should be verified as being completely empty or full.
Bilges should be dry.
10) The deck should be free of water. Any water trapped on deck will move during the test and reduce the
accuracy of the result.
11) The ship should be upright at the commencement of the experiment.
12) All personnel not directly concerned with the experiment should be sent ashore.
13) In tidal conditions, conduct experiments at slack water.
14) Efficient two-way communication must be established between a person in charge of the operation and
the central control station, the weight handlers, and each pendulum station.

Explain why a vessel’s Lightship KG may change over a period of time.

1) Accumulation of debris in enclosed spaces
2) Accumulation of sediments and mud in ballast tanks
3) Accumulation of coagulated residues in bunker tanks and bilges
4) Accumulation of paint coatings on internal and external surfaces
5) Accumulation of redundant spares
6) Accumulation of lost property on passenger ships
7) Changes to the ship's structure
8) Changes to internal furnishing particularly on passenger ships
9) Changes in vessel‟s equipment e.g., cargo handling gear
10) Removal of corrosion from the ship's structure

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List the circumstances when the inclining experiment is required to take place on
passenger vessel.
1) When the vessel is built.
2) When any major modifications are made to the ship to materially affect the stability.
3) Every 5 years.
4) If any significant change is found – Light displacement changed by 2% or Lightship LCG changed by
1% of the ship's length.

State the formula to determine the virtual loss of GM due to a free surface liquid
within a rectangular tank, explaining each of the terms used
The formula to determine the virtual loss of GM due to free surface liquid is given by

Free surface correction (FSC) = Loss in GM = L x B3 x RD of liquid in tank

12 x Δ x n2
Where

L = Length of the rectangular tank. The loss of GM is directly proportional to the length of the tank so will be
the value of free surface moments (loss of GM).
B = Breadth of the rectangular tank. From the formula, it can be seen that the breadth of the tank is the most
critical factor which determines the amount of loss in GM i.e., loss of GM is directly proportional to the cube of
the breadth of the tank.
Density = Relative density of liquid filled in the tank. The loss of GM is directly proportional to the RD of the
liquid, the greater the density of the liquid, the greater the loss in GM.
Δ = Displacement of the vessel. Greater the displacement of the vessel lesser the
loss of GM and vice versa.
12 = It is part of the formula. The free surface correction can also be given by
Free Surface Moments (FSM)
Displacement
FSM = Moments of Inertia of the free surface liquid x RD of the liquid
= L x B3 x RD of liquid
12
n = number of longitudinal subdivision of the tank. The longitudinal subdivision of the tank greatly reduces
the FSC as it is indirectly proportional to the square of the number of subdivisions. Further, it can be seen that if
the tank is divided into two equal subdivisions then the FSC will reduce by a quarter and 3 equal divisions will
reduce the loss by one-ninth and so on.

Explain the effects on the virtual loss of transverse GM due to the free surface
effects when the slack tank is subdivided

(a) Transversely:
Free surface correction (FSC) = Loss in GM = L x B3 x RD of liquid in tank
12 x Δ x n2

1. Although the tank is transversely subdivided yet the effective length and breadth of the tank still remain
the same.
2. One should not mistake „n‟ in the formula for transverse sub-division as it refers to the longitudinal sub-
division.
3. The area available for the free movement of the liquid still remains the same.
4. The free surface effect remains the same as it was before.
5. The following diagram shows an example of a tank transversely subdivided into two equal parts.

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(b) Longitudinally
Free surface correction (FSC) = Loss in GM = L x B3 x RD of liquid in tank
12 x Δ x n2

1. The longitudinal subdivision of the tank greatly reduces the free surface effect and hence the loss of
GM.
2. AS it can be seen from the formula, that the Loss in GM is inverse proportional to the square of the
number of subdivision (n2).
3. For example, if the tank is divided into two equal subdivisions then the FSC will reduce by a quarter
and 3 equal divisions will reduce the loss by one-ninth and so on.
4. The following figure illustrates an example of a tank longitudinally divided into two equal parts.

n n

Explain why a vessel laden to the same draught on different voyages may have
different natural rolling period.
Rolling period (T) in seconds is the time taken for the ship to complete one complete oscillation i.e., the time it
takes for the ship to roll from one side back through the upright to the extent of its roll on the other side and
back again. (port – starboard – port).

(1) The natural rolling period in still water is given by the formula:
T=2πK
√GM x g
Where
T = period of roll in seconds
g = acceleration due to gravity (9.81 mtrs / sec2)
K = Radius of Gyration.
GM = Metacentric height of the ship.
2) The radius of Gyration is the distance from the centre of gravity or the rolling axis at
which the total weight (W) would have to be concentrated to give the ship
same moment of inertia as it has.
3) For any particular ship, the Radius of Gyration can be changed by altering the distribution of
deadweight about the rolling axis. (affects the moments of inertia)
4) If the weights are moved away from the rolling axis, the radius of gyration is increased resulting in the
longer period of roll and the ship will roll slower (moving weight outwards towards the side of the ship
is known as winging out weights)
5) Conversely, moving weights inwards towards the rolling axis will cause the ship to roll faster.
6) The roll period varies inversely as the GM. Hence larger the GM, the shorter the rolling period (stiff
ship), and smaller the GM, the longer the rolling period (tender ships).
7) Also, the roll period will change when weights are loaded, discharged, or shifted since both the GM and
the moment of inertia (a measure of the distribution of weight about the rolling axis) will be affected.

From the above statement it can be seen that although the laden vessel has the same draught for different
voyages, yet its rolling period will change because of the following reasons:

CHANGE IN GM FOR THE SAME DRAUGHT:

1) For the same draught, the GM of the vessel may not necessarily be the same. GM of the vessel
varies with the concentration of weight distributed on the ship with reference to the keel.
2) A vessel loaded with high-density cargo (low SF) will have large GM (reduction in KG)
compared to when loaded with low-density cargo – both resulting in the same draught.
3) It is possible that the vessel may have loaded slightly less cargo but may have bunker tanks
completely filled which causes the G to move down increasing GM.
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 4) Also, the KG of the cargo loaded has a direct effect on the resultant GM of the vessel (For
example a vessel with more deck cargo will have less GM)
5) So the change in GM for the same draught will result in a change in the rolling period as
discussed above.

DISTRIBUTION OF WEIGHT WITH RESPECT TO ROLLING AXIS:

1) The Radius of Gyration may vary for every voyage (with the same draught) as the distribution of
weight concerning rolling axis may vary.
2) Hence the rolling period will change for each voyage.

However, it should be borne in mind that the period of roll is not affected by the amplitude or magnitude of the
roll.

Describe the different rolling characteristics of a vessel in a stiff condition and a

vessel in tender condition.
The natural rolling period for the vessel is given by
T=2πK
√GM x g
Where
T = period of roll in seconds
g = acceleration due to gravity (9.81 mtrs / sec2)
K = Radius of Gyration.
GM = Metacentric height of the ship.

Stiff Ship:
1) A stiff ship is one with a very large GM caused by the KG being too small.
2) This occurs if too much weight is placed low down within the ship.
3) The ship will be excessively stable, righting moments will be so large as to cause the ship to return to
the upright very quickly when heeled.

Rolling characteristics:
a) It can be seen from the above formula that the rolling period is inversely proportional to the GM of the
vessel.
b) Since the stiff ships have large GM, the rolling period will be short.
c) The ship will offer greater resistance to being rolled and will be rolled to lesser angles of heel.
d) Generally, a ship's natural rolling period is greater than the wave period. Since stiff ships have shorter
rolling period they are more vulnerable in the beam sea.

Tender Ships:
1) A tender ship is one with a very small GM caused by KG being too large.
2) This occurs if too much weight is placed high up within the ship.
3) The ship will have less stability, righting moments as compared to the stiff ship.
4) This causes the ship to be a sluggish and slow to return to the upright.

Rolling characteristics:
a) Because of small righting moments, the ship will only offer limited resistance to being rolled, causing
the ship to be rolled to larger angles of heel.
b) Also from the Rolling period formula, the Rolling period varies inversely as GM.
c) Since the tender ships have small GM, their rolling period will be long.
d) The ship will be slow to return to the upright and will tend to remain at the extent of the roll for a
comparatively long time.

The Radius of Gyration also has an effect on the ship's rolling characteristics. However, in both Stiff and
Tender ship, it varies with the circumstances as the distribution of weight with respect to rolling axis is not
the same at all times.

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Discuss how a vessel’s still water rolling period is affected by changes in the
distribution of weight aboard the vessel.
The distribution of weight aboard the vessel can be discussed with respect to the following factors:

(1) Distribution of weight with respect to the Keel of the vessel (KG of the weight)
(2) The relative density of the weight is distributed.
(3) Distribution of weight with respect to the rolling axis.

Distribution of weight with respect to the Keel of the vessel (KG of the weight)

If the weight is distributed high up within the vessel, then the resultant GM if the vessel will be reduced due to
an increase in the resultant KG of the vessel. (because the KG of the weight distributed will be more).

The relative density of the weight is distributed.

The relative density or the SF of the weight distributed will contribute a major factor in determining the GM of
the vessel. For example, if a high-density cargo is loaded in a ship then the GM of the vessel will increase as
compared to loading a low-density cargo in the same hold.

Thus it can be seen that both the above factors are affecting the GM of the vessel.

Distribution of weight with respect to the rolling axis

The distribution of weight with respect the to rolling axis affects the Radius of Gyration. If weights are
distributed inwards towards the rolling axis then the Radius of Gyration is reduced. Conversely, if the weights
are distributed away from the rolling axis the radius of gyration is increased.

The natural rolling period for the vessel is given by

T=2πK
√GM x g
Where
T = period of roll in seconds
g = acceleration due to gravity (9.81 mtrs / sec2)
K = Radius of Gyration.
GM = Metacentric height of the ship.

Using the above formula in conjunction with the explanation of the above section it can be seen that:

1) The distribution of weight aboard the vessel can change the GM of the vessel.
2) The Rolling period varies inversely as the GM and hence change in GM changes the rolling
period.
3) Also, the distribution of weight with respect to the rolling axis affects the Radius of Gyration.
Therefore the distribution of weight is such that if the Radius of Gyration is increased then the
rolling period is increased as it is directly proportional and vice versa.

Explain the term Synchronous rolling and describe the dangers if any associated
with it.
Synchronism is the name given to the condition when the ship's natural period of roll is the same as the apparent
period of the wave.

1) When this occurs the waves give the ship a push each time she rolls (like a swing) causing her to roll
more and more heavily.
2) Theoretically, this could cause the vessel to eventually capsize.
3) However, Synchronism is less likely to happen as the rolling period of the ship increases with the angle
of roll at large angles of heel.
4) Moreover, the period of sea waves tends to vary over time.
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 5) The ship‟s natural rolling period will be greater than the wave period.
6) Ships which has a long natural rolling period is less vulnerable in a beam swell than the stiff ships with
their short periods of roll.
7) If the sea is forward of the beam the apparent period of waves will be reduced whilst the sea abaft the
beam will increase the apparent period of waves.
8) Therefore the sea on the quarter will increase the likelihood of synchronism.

Dangers associated with Synchronous rolling:

a) The danger of capsizing the vessel.
b) A heavy roll may cause a shift of cargo, especially deck cargo which is at a greater distance from the
rolling axis.
c) The vessel will then roll in a fashion dictated by righting moment, heeling the vessel excessively to the
listed side and increasing the chances of a subsequent shift of. Cargo.
d) The dynamical stability of the vessel will be greatly reduced under these circumstances and there is
always a risk of capsizing.
e) Structural damage to the vessel (racking, surge of liquids).
f) Personal injury.
g) Down flooding.

State the action to the taken by the ship’s officer when it becomes apparent that
the vessel is experiencing Synchronous rolling.
1) Alter course, ideally towards the wave since this shortens the apparent period of the waves.
2) Alter speed except when the wave is not on the beam.
3) Alter vertical distribution of the weight to change the GM.
4) Alter the vertical and transverse distribution of the weight aboard the vessel to change the ship's radius
of gyration. E.g., winging out weights.
5) The latter two measures can be achieved by ballasting, deballasting, or shifting other items of
deadweight such as fuel or freshwater.

Describe the methods of improving the initial stability if the GM at the critical
instant is found to be inadequate.

The major considerations that should be borne in mind during dry-docking are
1) that the P force is kept to an acceptable level and
2) that the Ship maintains an acceptable positive GM during the critical period.

Loss of GM = P X KG (OR) P X KM
Δ–P Δ
If it is found that the GM at a critical instant is found to be inadequate the following measures to be taken to
improve the initial stability.

1) The loss in GM is directly proportional to the KG of the vessel. Hence lower the effective KG of the
vessel by lowering the weights within the vessel, discharging weights from the high up, or taking on an
acceptable amount of ballast in the double bottom tanks.
2) Empty the high wing tanks if possible.
3) Stow derricks, cranes, and riggings in a stowed position.
4) Eliminate or minimize free surface effects by topping up or emptying slack tanks where possible.
5) Keep minimum stern trim as recommended by the dry docking plan. Smaller the trim, the smaller the P
force and hence smaller the loss of GM.

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Explain why the values of trim and metacentric height in the freely afloat
conditions are important when considering the suitability of a vessel for
drydocking.
Trim:

1) The trim of the vessel plays a very vital roll in the vessel's dry-docking.
2) The vessel should enter the dry dock with a small stern trim as recommended by the dry docking plan
available on the ship.
3) „P‟ force or the upthrust generated at the block when the vessel‟s stern first touches the block continues
to increase as the buoyancy force is reduced.
4) The formula for calculation of the „P‟ force is given by
P= Change of Trim X MCTC
LCF
5) From the formula, it can be seen that the greater the stern trim more the 'P' force.
6) Although the stern frame is designed to take force exerted on it during dry-docking, there is a maximum
limit that must not be exceeded.
7) If the „P‟ force is exceeded then it will lead to structural damage.

Metacentric Height (GM):

1) Loss of stability (Loss of GM) commences as soon as the ship touches the block aft and continues to
worsen as the value of the P force increases.
2) The maximum loss of GM occurs at the instant immediately before the ship settling on the blocks
forward and aft – known as Critical Instant.
3) The vessel must have positive stability (positive GM) at this critical instant.
4) The righting moment afforded by the upward acting buoyancy force (remaining – due to pumping out
of dock water) must remain greater than the capsizing moment afforded by the upthrust of P force
acting at the keel at all times before the ship touching the blocks forward and aft.
5) If this is not so, then the ship will become unstable resulting in negative GM and would topple over in
the dock.
6) Therefore the metacentric height of the vessel when she is in freely afloat condition is very important
when considering the suitability of the vessel for dry-docking.
7) The formula for loss of GM at the critical instant is given by
Loss of GM = P X KG (OR) P X KM
Δ–P Δ
8) From the formula, it can be seen that loss of GM is directly proportional to the P force and the KG of
the vessel.

Hence the values of trim and metacentric height of the vessel in the freely afloat conditions are important for
dry docking the vessel.

Describe the two methods of determining the upthrust (P force) during the critical
period.
The two methods of calculating the P force are
a) Calculation of P force at any stage during the dry-docking process.
b) Calculation of P force during the critical period when dry-docking.

Calculation of P force at any stage during the dry-docking process.

1) Throughout the dry-docking procedures, the true mean draught of the vessel reduces.
2) This situation is similar to the vessel rising out of water due to weights being discharged.
3) The rise in cms is given by the formula w(t) ÷ TPC.
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 4) The 'P' force may be considered to have the same effect on True mean draught as if weight had
been discharged.
5) Therefore reduction in TMD (cms) = P force (t)
TPC
6) Transposing this formula we can find that
P force (t) = Reduction in TMD (cms) x TPC
7) This formula can be used at any draught before or after the critical instant since what is being
found is the loss in buoyancy due to the reduction in the draught.

Calculation of P force during the critical period when dry-docking.

a) In the period between the ship touching the block aft (start of critical period) and touching the blocks
forward and aft (critical instant), the ship changes trim.
b) The change of trim at any stage during the critical period may be considered to be the same as the
change of trim that would have occurred when a weight 'w' has been discharged from a position at the
aft perpendicular equivalent to the upthrust 'P' in tonnes.
c) The formula to find the change of trim is given by
COT (cms) = Trimming Moment = w x LCF
MCTC MCTC
d) If the P force is considered to have the same effect as a weight discharged at the aft perpendicular, then
COT (cms) = P x LCF
MCTC
e) Transposing the above formula we can find P as given under
„P‟ force at any instant during critical period = COT(cms) x MCTC
LCF foap

Explain why it is beneficial to have small stern trim when entering the dry dock.
Small:
1) Smaller the trim, the smaller the P force at the CI and therefore smaller the loss of GM prior to
taking the blocks fore and aft.
The formula for calculating the P force is given by COT(cms) x MCTC
LCF foap

Loss of GM = P X KG (OR) P X KM
Δ–P Δ
2) It can be seen from the above two formulas that small trim will reduce the P
the force exerted during docking and subsequently the loss of GM

Stern:
The stern frame is stronger than the bow and therefore better able to bear the P force when the vessel is
touching the blocks.

Trim:
It is much easier to align the vessel‟s keel over the keel blocks in the DD than if the vessel had gone on E.K and
also because of the declivity of the DD.

A ship is loading in a port in a tropical zone for one in the Winter North Atlantic
zone during winter months.
Describe the various precautions and considerations which must be borne in mind
at the loading port so that the voyage is accomplished safely and in accordance
with the statutory requirements, for example, the Load Line rules.

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 1) The primary consideration is to have the vessel complying with the load line regulations throughout the
voyage for ensuring intact reserve buoyancy - Cargo hatches, ventilators, sounding pipes, air pipes,
freeing port)
2) Since the vessel is going to another Load line zone, the vessel should be loaded in such a way she does
not breach the load line requirements.
3) Although she is loading in Tropical zone, yet she cannot immerse the marks more than a lever i.e.,
Winter load line + due allowance for consumables + bunkers.
4) To calculate the bunker consumption and FW consumption up to a point on the vessel‟s intended route
where it enters the winter load line zone.
5) Also the loading should be in such a way that the vessel will have adequate stability.
Initial GM not less than 0.15 mtrs
for timber ships not less than 0.05 m.
The maximum righting lever (GZ) at least 0.20 mtrs
Angles of Maximum GZ not be less than 30 degs
Area under the curve
0 to 30 degs not less than 0.055 mr
0 to 40 degs or θf whichever is lesser not less than 0.09 mr
Between 30 degs and 40 degs or θf not less than 0.03 mr

6) If the ship is less than 100 mtrs in length she cannot immerse more than winter north Atlantic mark
when in the winter zone.
7) Vessel needs to have sufficient bunker reserve to meet bad weather and contingencies.
8) All derricks and cranes must be stowed in position.
9) Eliminate free surface effects by emptying or pressing the tanks if possible.
10) Adequate lashing arrangements for deck cargoes particularly for heavy lifts.
11) Stow heavy cargo as low as possible to bring down G.
12) The vessels loading and stability condition throughout the voyage must take into account ice
accretion.
13) Fire lines and steam lines must be drained.
14) Shearing force, bending moments and Torsional stresses must be well within limits.

Describe Type 'A' vessel under the current Load line Regulations, including the
flooding, Stability, and assumed damage requirements for a newly built
vessel.
According to Regulations 27 of Loadline Regulations a type 'A' ship is defined as one which:
1) is designed to carry only liquid cargoes in bulk.
2) Has high integrity of the exposed deck with only small access openings to cargo compartments, closed
by watertight gasketed covers of steel or equivalent material
3) Has a low permeability of loaded compartments.
4) Has a high degree of sub-divisions.

Flooding requirements:
1) If the vessel is over 150 mtrs in length and has an empty compartment when fully loaded at the Summer
loadline, the ship should be capable of remaining afloat after the flooding of such a compartment with
an assumed permeability of 0.95 and shall remain afloat in a satisfactory condition of equilibrium.
2) If the vessel is over 150 mtrs in length then the machinery space shall be treated as a floodable
compartment, with an assumed permeability of 0.85.

Stability requirements: - Condition of Equilibrium

1) The final waterline after flooding, taking into account sinkage, heel, and trim, is below the
lower edge of any openings such as air pipes, top of a ventilator coaming, door sill, and
openings which are closed utilizing weathertight doors or hatch covers through which
progressive flooding may take place.
2) The angle of heel due to unsymmetrical flooding does not exceed 15 degs.
3) If no part of the deck is immersed, an angle of up to 17 degs may be accepted.
4) The metacentric height (GM) in the flooded condition must be positive and must be at least
0.05m.
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 5) The vessel must have adequate residual stability after flooding
6) The right lever curve must have a minimum range of stability of 20 degs.
7) The maximum righting lever (GZ) must be at least 0.1 mtrs within this range of stability.
8) The residual area under the righting lever curve within this range shall not be less than 0.0175
mr.

Damage assumptions:
1) The vertical extent of damage in all cases is assumed to be from the baseline upwards without limits. -
Keel to deck
2) The transverse extent of damage is equal to 20% of beam or 11.5 mtrs whichever is lesser.
3) Longitudinally – Between transverse bulkhead (B-100 to include one bulkhead other than machinery
space bulkhead)

Describe the provisions of the current Load Line regulations governing the ability
of some Type B vessels to withstand flooding due to damage and the stability in the
final conditions.
1) A type B ship is one which is not a Type A ship –not designed to carry liquid cargoes in Bulk.
2) Has a greater freeboard than type A vessel.
3) Has a lesser degree of sub-division.
4) Has large deck openings which are only weather-tight.
5) Access to under deck compartments in Type B vessels is through large hatches.

There are two classifications of Type B vessels viz., Type B-60 and Type B-100

Type B-60:
1) Any type B ship which is over 100 mtrs long.
2) Have hatchways closed by weather-tight steel covers
3) Since provided with steel hatch covers, qualifies for a reduction in the tabular freeboard of 60% the
difference between type A and type B freeboards, hence the term B-60.
4) Flooding requirement
a) When loaded in accordance with the initial condition of loading, shall be able to withstand the
flooding of any single compartment with an assumed permeability of 0.95 and shall remain
afloat in a satisfactory condition of equilibrium.
b) If the vessel is over 150 mtrs in length then the machinery space is regarded as a floodable
compartment with assumed permeability of 85%
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 Type B 100
(a) Any type of B 60 ship over 100 mtrs long.
(b) Provided with steel hatch covers which are watertight.
(c) Access to the engine room from deck protected by house.
(d) Provided with open rails for 50% of the length of the vessel and not bulwark.
(e) Crew access by gangway or under deck passage.
(f) Qualifies for a reduction in the tabular freeboard of 100% the difference between type A and type B
freeboards, hence the term B-100.
(g) Flooding requirement:
a. When loaded in accordance with the initial condition of loading, shall be able to withstand the
flooding of any two fore and aft adjacent compartment with an assumed permeability of 0.95
and shall remain afloat in a satisfactory condition of equilibrium.
b. If the vessel is over 150 mtrs in length then the machinery space is regarded as a floodable
compartment with assumed permeability of 85%

Condition of Equilibrium – Applicable all classes of Type B vessels.

1) The final waterline after flooding, taking into account sinkage, heel and trim, is below the lower edge
of any openings such as air pipes, top of a ventilator coaming, door sill, and openings which are closed
utilizing weathertight doors or hatch covers through which progressive flooding may take place.
2) The angle of heel due to unsymmetrical flooding does not exceed 15 degs.
3) If no part of the deck is immersed, an angle of up to 17 degs may be accepted.
4) The metacentric height (GM) in the flooded condition must be positive and must be at least 0.05m.
5) The vessel must have adequate residual stability after flooding
6) The right lever curve must have a minimum range of stability of 20 degs.
7) The maximum righting lever (GZ) m 0.1 mtrs within this range of stability.
8) The residual area under the righting lever curve within this range shall not be less than 0.0175 mr.

When converting tabular freeboard into assigned Freeboard as specified in the

Load Line rules several corrections have to be applied. With the aid of simple
sketches describe each of the corrections and indicate how each may be applied.

A tabular freeboard is a freeboard that would be assigned to a standard ship built to the highest recognized
standards having specific characteristics as laid down in the Load Line Regulations.

The following corrections required to be applied to convert Tabular freeboard to assigned freeboard.

Type B-60 / B-100 correction – For type B vessels only:

1) If the ship qualifies for the reduction in tabular freeboard, either 60% or 100% then this correction is
applied.
2) Qualification requires the provision of steel hatches, subdivision, improved water freeing arrangements,
crew protection, etc.

Wooden Hatch correction – for type B vessels only:

The tabular freeboard is increased if the vessel has hatches other than those of the steel pontoon type on the
exposed freeboard deck / raised quarter deck or the forward 25% of the superstructure deck (i.e., Position 1)

Flush deck correction – only Type B ships:

1) This correction is applicable if :
a) The length of the vessel is less than or equal to 100 mtrs and
b) The effective length of the superstructure is less than or equal to 35% of ships
length.
2) The tabular freeboard in this case is increased.

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Block co-efficient correction:
1) The block co-efficient is measured at 85% of the vessel‟s moulded depth.
2) Modified tabular freeboard is increased if the block co-efficient of the vessel exceeds 0.68.
3) Freeboard is multiplied by (0.68 + Cb) ÷ 1.36.

Depth correction:
1) The standard freeboard depth of a ship under the Rules = L ÷ 15
2) If the freeboard depth is more than L ÷ 15, then the freeboard is increased
3) If the freeboard depth is less than L ÷ 15, the freeboard may be decreased provided that the
superstructure is at least 0.6 L amidship or trunk over the entire length of the vessel.

Correction for the position of deck line:

1) The freeboard must be capable of vertical measurement.
2) If the vessel is having a rounded gunwale, then the freeboard must be corrected by the vertical
difference between the actual position of the deck line and the correct position.

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Superstructure correction:
1) Freeboard will be reduced if:
(a) The ship is with sufficient standard height superstructure (OR)
(b) Has sufficient watertight trunking to a minimum height and width.
2) This reduction will vary according to the length of the superstructure /trunk as a percentage of the
vessel's length.
3) If the superstructure or trunk is of less than the standard height/breadth then the correction will be
reduced proportionally.
4) If it is not of sufficient height (or) % length (or) width then no reduction in freeboard.

Sheer correction:
1) Load line regulations assume a standard sheer for the vessel.
2) If the vessel has a greater sheer than standard, the basic freeboard is decreased.
3) If the vessel has a lesser sheer than the standard, the basic freeboard is increased.
4) No reduction in freeboard if the vessel does not have a superstructure covering 10% length forward and

aft of midship.

Bowheight correction:

1) The load line rules contain a formula for calculating the minimum bow height based on the vessel's
length and block co-efficient.
2) If the bow height is less than the calculated height, the freeboard is increased accordingly.

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Summer Freeboard: - Assigned only upon Owners' request – only increase in freeboard.
Freeboards may also be increased at the owners' request (or) where there are openings or cargo portholes
below the freeboard deck

Corrections are then applied to the Assigned Summer Freeboard to determine the Tropical, Winter, Fresh
Water, and Tropical Freshwater freeboards.

When converting TABULAR FREEBOARD to BASIC FREEBOARD as specified

in the Load line Rules several corrections have to be applied.

(a) List the geometric features of the ship which give rise to these corrections.
The ships which are required for these corrections are Type B vessels.

1) A type B ship is one which is not a Type A ship –not designed to carry liquid cargoes in Bulk.
2) Has a greater freeboard than type A vessel.
3) Has a lesser degree of sub-division.
4) Has large deck openings which are only weather-tight.
5) Access to under deck compartments in Type B vessels is through large hatches.
There are two classifications of Type B vessels viz., Type B-60 and Type B-100

Type B-60:
1) Any type B ship which is over 100 mtrs long.
2) Provided with steel hatch covers which are weather tight.
3) Since provided with steel hatch covers, qualifies for a reduction in the tabular freeboard of 60%
the difference between type A and type B freeboards, hence the term B-60.
Type B 100
1) Any type of B 60 ship over 100 mtrs long.
2) Provided with steel hatch covers which are weather tight.
3) Access to the engine room from deck protected by house.
4) Provided with open rails for 50% of the length of the vessel and not bulwark.
5) Crew access by gangway or under deck passage.
6) Qualifies for a reduction in the tabular freeboard of 100% the difference between type A and
type B freeboards, hence the term B-100.

(b) Explain the reason for each of these corrections and indicate how each correction should be applied to
Tabular Freeboard (actual values not required)

Type B-60 / B-100 correction

B-60 : Since provided with steel hatch covers, qualifies for a reduction in the tabular
freeboard of 60% the difference between type A and type B freeboards, hence the
term B-60.
B-100: Qualifies for a reduction in the tabular freeboard of 100% the difference between
type A and type B freeboards, hence the term B-100.

Wooden Hatch correction:

The tabular freeboard is increased if the vessel has hatches other than those of the steel pontoon type on the
exposed freeboard deck / raised quarter deck or the forward 25% of the superstructure deck (i.e., Position 1)
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Flush deck correction:
1) This correction is applicable if :
a) The length of the vessel is less than or equal to 100 mtrs and
b) The effective length of the superstructure is less than or equal to 35% of ships
length.
2) The tabular freeboard in this case is increased.

Block co-efficient correction:

1)The block co-efficient is measured at 85% of the summer draught.
2) Modified tabular freeboard is increased if the block co-efficient of the vessel
exceeds 0.68.
3) Freeboard is multiplied by (0.68 + Cb) ÷ 1.36.

State with the aid of a labeled sketch, the minimum stability criteria required by
the current Load line Rules.

Initial GM not less than 0.15 mtrs

The maximum righting lever (GZ) at least 0.20 mtrs
Angles of Maximum GZ not be less than 30 degs
Area under the curve
0 to 30 degs not less than 0.055 mr
0 to 40 degs or θf whichever is lesser not less than 0.09 mr
Between 30 degs and 40 degs or θf not less than 0.03 mr

The current Load line rules permit a reduction of the permissible minimum initial
GM for some vessels with timber deck cargo and the inclusion of the volume of
this cargo in the derivation of the cross curves.
Outline the circumstances under which this reduction is allowed and explain why
this reduction is permitted.
1) The vessel must have a timber certificate.
2) Must have Assigned Timber Freeboard.
3) Must have solid stow of deck cargo full length of the deck.
4) The vessel must have positive stability at all times and should be calculated concerning:
a) the increase of timber weight due to
absorption of water.
Ice accretion if applicable.
b) variations in consumables.
c) Free surface effects of the liquids in tanks.
d) Weight of water trapped in the broken spaces within the timber deck cargo especially logs.
5) The stability calculations should include a 15% increase in weight due to water absorption during the
voyage.
6) KN values may be increased for additional freeboard BUT only 75% of the deck cargo volume may be
used for additional reserve buoyancy.

The reason for the reduction in the minimum permissible GM is as follows:

1) The deck cargo secured stowed on the full length of the freeboard deck acts as additional reserve
buoyancy.
2) The additional reserve buoyancy is applicable only when the deck cargo is well secured and covers the
entire length of the ship's cargo deck up to at least standard superstructure height.
3) The timber cargo also provides a greater degree of protection for the hatches against the sea.
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 4) The KN values may be increased for additional freeboard however only 75% of the timber volume must
be considered as reserve buoyancy.
5) The principle of inclusion of the timber as reserve buoyancy in the derivation of the alternative KN data
is illustrated in the following figure.

G Z
G Z
B
B

Fig „A‟ Fig „B‟

From the above diagram

1) In figure A when the vessel is heeled beyond the angle of deck edge immersion, GZ values are small
when reserve buoyancy of the timber is not included i.e., the GZ values are derived from the ship's
ordinary KN values.
2) In figure B we can see that by using KN values which include 75% of the volume of the immersed
timber as reserve buoyancy caused an outward movement of B which increased the GZ values.
3) This increase in GZ value increases the range of stability of the vessel and the dynamical stability.

Concerning Load Line rules distinguish a Type A vessel from a Type B vessel and
explain why they have different TABULAR freeboards.
TYPE A TYPE B
1) Designed to carry liquid cargo in bulk Other than Type A vessels – which are not
designed to carry liquid cargo in bulk
2) Allows a small freeboard i.e., less reserve Has a greater freeboard than Type A
buoyancy.
3) The longitudinal hull framing in Type A Has less degree of sub-division.
vessels results in a high degree of sub-
divisions
4) Exposed weather deck has a high degree Exposed weather deck has a low degree of
of integrity. integrity as compared to Type A vessel
Access to under deck compartment is Access to under deck compartment is through
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 through small deck openings which are large hatch openings which are only weather
watertight steel covers tight.
5) A high degree of safety against flooding Vulnerable in heavy weather to flooding
because of the low permeability of loaded
cargo spaces.
6) Has a high degree of sub-division Less degree of sub-division

Type A vessel and Type B vessel have different tabular freeboard because:
1) The structural layout of both vessels are different
2) The types of cargo carried are different.
3) Moreover, the permeability of the cargo tanks in Type A ships is low as compared to the Type
B ship.
4) Therefore in an event of flooding of a compartment, oil from the cargo tank of Type A vessel
will run out causing a decrease in displacement and an increase in freeboard, whereas in the
case of type B ship, the seawater will enter the cargo space resulting in an increase in draught
and reduction in freeboard.

State the general requirement for a TYPE B vessel to be given the same
TABULAR freeboard as TYPE A vessel of the same length.
A type B vessel can be given the same TABULAR freeboard as a Type A vessel of the same length if the
following criteria are satisfied:

Any Type B-60 ships of over 100 mtrs long (Type B-100) satisfying the following conditions at summer
draught:
5) Provided with steel hatch covers which are weather tight.
6) Access to the engine room from deck protected by house.
7) Provided with open rails for 50% of the length of the vessel and not bulwark.
8) The weather deck must be fitted with a protected raised catwalk or under deck ways to allow
safe access for the crew.
9) Shall remain afloat after flooding of any two fore and aft adjacent compartment with an
assumed permeability of 95% at summer draught

Identify the additional corrections required when converting BASIC

FREEBOARD to ASSIGNED FREEBOARD, explaining the reason for each
correction.
Depth correction:
4) The standard freeboard depth of a ship under the Rules = L ÷ 15
5) If the freeboard depth is more than L ÷ 15, then the freeboard is increased
6) If the freeboard depth is less than L ÷ 15, the freeboard may be decreased provided that the
superstructure is at least 60% of length amidship position or trunk over the entire length of the vessel.

Correction for the position of deck line:

3) The freeboard must be capable of vertical measurement.
4) If the vessel is having a rounded gunwale, then the freeboard must be corrected by the vertical
difference between the actual position of the deck line and the correct position.

Superstructure correction:
5) Freeboard will be reduced if:
(a) The ship is with sufficient standard height superstructure (OR)
(b) Has sufficient watertight trunking to a minimum height and width.
6) This reduction will vary according to the length of the superstructure/trunk as a percentage of the
vessel's length.
7) If the superstructure or trunk is of less than the standard height/breadth then the correction will be
reduced proportionally.
8) If it is not of sufficient height or % length or width then no reduction in freeboard.
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Sheer correction:
5) Load line regulations assume a standard sheer for the vessel.
6) If the vessel has a greater sheer than standard, the basic freeboard is decreased.
7) If the vessel has a lesser sheer than the standard, the basic freeboard is increased.
8) If the vessel's amidships superstructure is less than 10% length, then there is a reduction in
freeboard.
Bowheight correction:

3) The load line rules contain a formula for calculating the minimum bow height based on the vessel's
length and block co-efficient.
4) If the bow height is less than the calculated height, the freeboard is increased.

Summer Freeboard: - Assigned only upon Owners' request – only increase in freeboard.
Freeboards may also be increased at the owners' request or where there are no openings or cargo portholes
below the freeboard deck

Corrections are then applied to the Assigned Summer Freeboard to determine the Tropical, Winter, Fresh
Water, and Tropical Freshwater freeboards.

Describe the general provisions of the current Passenger Ship Construction Rules
governing the ability of a Class I Passenger vessel to withstand flooding due to
damage, and the stability in the final condition.

General Requirements:
1) The margin line is the waterline and must be at least 76mm below the upper surface of the bulkhead
deck.
2) The floodable length depends upon the permeability of the compartment.
(a) Permeability for cargo and store spaces = 60%
(b) Machinery spaces = 85%
(c) Passenger spaces = 95%
3) The vessel should remain afloat in the event of damage to any compartment.
4) The factor of sub-division (to determine max spacing between transverse bulkhead) varies inversely
with the ship's length, the number of passengers and the proportion of underwater space used for
passenger/crew and machinery space.
5) A greater degree of subdivision (or small factor of subdivision) must be provided when
(a) The vessel is long
(b) The number of passengers is large
(c) Much space below the waterline is used for passenger/crew accommodation and/or machinery
space.
6) The permitted length between bulkhead = Floodable length x Factor of sub-division.

Assumed damage:
1) Vertical extent is from keel to deck
2) Transverse extent must be 20% of the Beam of the vessel.
3) Longitudinal extent of the damage must be:
a) 11 mtrs between bulkhead (OR)
b) 3m + 3% of the length of the vessel, WHICHEVER IS THE LEAST

Assumed Flooding:
The vessel must be able to withstand the flooding of the following number of compartments (final waterline at,
or below margin line)
1) Factor of sub-division more than 0.5 THEN Any one compartment
2) Factor of sub-division between 0.5 and 0.33 THEN Any 2 adjacent compartments
3) Factor of sub-division 0.33 or less THEN Any 3 adjacent compartments
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Required Stability after Flooding:

In the final stage, after any equalization (CROSS FLOODING) measures, the vessel must comply with the
following condition:

1) Residual GM at least 50mm.

2) Final heel not to exceed:

a) 7 degs with one compartment flooding (OR)
b) 12 degs if two or more compartment is flooded.

3) Positive residual GZ curve with a range of at least 15 degs

4) Area under residual GZ curve to be at least 0.015 mr up to:

Either
a) 22 degs – for one compartment flooding (OR)
b) 27 degs – for two-compartment flooding (OR)
c) Angle of progressive flooding θf
WHICHEVER IS LEAST

5) Maximum residual righting lever to be at least either:

a) 10 cms (OR)
b) Heeling moment + 0.04 m WHICHEVER IS GREATER
Displacement

6) The heeling moments to be calculated from:

a) Crowding of all passengers towards one side (OR)
b) Launching of fully loaded davit launch survival craft, (OR)
c) Wind pressure
WHICHEVER IS BIGGEST

Regarding the current Passenger Ship Construction and Survey Regulations

(a) Explain the extent of hull flooding assumed when calculating the ship’s ability
to survive hull damage.
To arrive at the minimum required stability for the Passenger vessels after suffering flooding of compartments,
the following two factors are taken into consideration:

1) Assumed Flooding
2) Assumed damage.

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Assumed Flooding
The number of compartments involved in the assumed flooding conditions is based upon the Factor of sub-
division. Lesser the factor of sub-division, the lesser the Permissible length of the compartment and hence more
the number of compartments taken into consideration for assumed flooding. However, at any instant, not more
than 3 compartments are assumed to be in a flooded condition.

The vessel must be able to withstand the flooding of the following number of compartments:
1) Factor of sub-division more than 0.5 THEN Any one compartment
2) Factor of sub-division between 0.5 and 0.33 THEN Any 2 adjacent compartments
3) Factor of sub-division 0.33 or less THEN Any 3 adjacent compartments

Assumed damage:
1) Vertical extent is from keel to deck
2) The transverse extent must be 20% of the Beam of the vessel.
3) The longitudinal extent of the damage must be:
a) 11 mtrs between bulkhead (OR)
b) 3m + 3% of the length of the vessel, WHICHEVER IS LEAST
4) If the damage of a lesser extent than indicated above would result in a more severe
condition regarding heel and GM loss, such damage shall be assumed for the calculation.

(c) Outline the additional factors taken into account to determine the
permissible length of compartments in ships built after 1990.
Permissible length of the compartment having its centre at a point in the length of the ship means the product of
the floodable length at that point and the factor of subdivision of the ship.

Permissible length = Floodable length x Factor of Sub-division.

The features of the ship that are considered in determining the length for the purpose of subdivision calculation
includes:
1) Block co-efficient of the vessel
2) Freeboard ratio
3) Sheer Ratio
4) Compartment permeability
5) Length of the vessel
6) Number of passengers.
7) The proportion of the underwater space used for passengers/crew and machinery space

The permissible length between the compartments is reduced (due to decrease in the Factor of sub-division)
when
1) The length of the ship is more
2) More number of passengers are carried
3) Much of the space below the waterline is used for passenger/crew accommodation and or machinery
space.

Describe the Stockholm agreement with reference to the stability requirement of Passenger Ro-Ro vessels.

Purpose of the Stockholm agreement:

1) Lays down the stability requirement for Passenger Ro-Ro vessel.
2) The agreement concluded after the disaster of Estonia
3) Signed between nine northern European states in 1996.
4) These upgrades SOLAS 90 standards.
5) Takes into account the effect of water accumulation on the vehicle deck after damage, making the ship
safer in heavy seas.

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 6) Applies to all Passenger Ro-Ro vessels operating on scheduled international voyages between or from
designated ports in northern Europe irrespective of Flag.

Requirements by the Agreement:

1) Demands that a vessel satisfies with the requirement of SOLAS 90 with a constant height of water on
deck.
2) The height of water on the vehicle deck is based on a 4.0 mtr significant wave.
3) The height of water should be
a) 0.5mtrs if the residual freeboard at the damage opening is 0.3 mtrs or less
b) 0.0 mtrs if the residual freeboard at the damage opening is 2.0 mtrs or more
4) Intermediate values can be determined by linear interpolation

Describe the stability problems associated with a conventional Ro-Ro ferry.

The stability of vehicle ferries poses particular problems due to the following:

Free Surface Effect:

(a) Because the vehicle deck usually extends over the length and breadth of the vessel without
restriction, this type of vessel is especially vulnerable to the effects of free surface
(b) Such a vessel may rapidly lose all stability and capsize if the vehicle deck becomes flooded.
(c) Causes of such flooding include
 Damage to bow or stern door at sea
 Bow or stern door left open at sea
 Bow or stern door open and unattended during loading / discharging operations.
 Loss of watertight integrity due to collision with another vessel or rocks.
 Loss of watertight integrity due to the shift of a vehicle in heavy seas.
 Use of water curtains (coupled with inadequate drainage)

Inadequate Stability Information due to:

1) Speed of turnaround in port.
2) Lack of detailed information about cargo units and disposition

Other factors:
1) High KG of cargo units on the vehicle deck
2) The vulnerability of Ro-Ro units to shifting in bad weather.
3) High Windage area of Ro-Ro vessels.

What precautionary measures must be adopted to improve the stability of Ro-Ro

ferries
1) Automatic draught gauges at the stem and stern with remote readout should ensure that flooding of the
vehicle deck in port is avoided.
2) A loading computer must be available to the ship‟s officer in port for rapid calculation of stability before
the vessel sails.
3) Indicator lights must be provided on the bridge to show when shell/loading doors are open/closed.
4) Heavy Ro-Ro cargo units must be weighed ashore and the information provided to the ship's officers.
Such units must be secured by chains to the deck before departure.
5) Increased drainage requirements for vehicle decks.
6) Stockholm agreement provides enhanced stability requirements for Ro-Ro passenger ferries with 50 cms
of water on the vehicle deck.
7) Provision of some form of sub-division on the vehicle deck.

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Discuss the stability problem associated with the design and operation of a
conventional Oil Rig supply vessel.
The stability of the Offshore supply vessel poses a particular problem due to the following:

Loading and/or Discharging cargo at sea:

1) Affects the vertical, transverse, and longitudinal position of the G of the vessel.
2) This is of particular relevance since cargo operations may be taking place as the vessel is rolling and
pitching in a seaway.
3) The cargo is often in liquid form (water, fuel, mud, etc) which will result in virtual loss of stability due
to FSE during the cargo handling operation.

Excessive Stern Trim

1) Occurs through the longitudinal distribution of loaded weight.
2) It may occur during an ill-advised discharge/load, or when working with cables/anchors.
3) Considerable stern trim develops during these stages.
4) This may cause the working deck to become awash thereby reducing the waterplane area and critically
reducing the vessel's stability.

Water entrapment
The working deck is often used to carry drill supplies, machinery, pipes, etc., some of which have been found to
retain a large amount of water due to seas on the after deck. An allowance for such volume of water entrapped
must be made in the stability calculation.

Free Trim
1) Free trim affects the GZ curve of the vesse.
2) There is a reduction in the stability after the angle of deck edge immersion due to vessel trimming by
stern due to rolling.
3) This is caused by the after deck becoming awash and reducing the waterplane area when the vessel is
heeled in a seaway.

Stabilizer Tank
1) Many vessels are fitted with flume stabilizer tanks
2) These can be counter-productive in some sea conditions for example when working cargo or working
cables over side.
3) This is because a heeling arm is produced which results in water in the stabilizer tank moving to the low
side in passive flume tanks thereby increasing the list.
4) Furthermore they will generate a significant FSE which will reduce the vessel‟s stability and should be
allowed for.

What are the recommended measures to improve the stability of the Offshore
supply vessels?
1) Discharge from top of stow first.
2) Consider the use of ballast to counteract any negative effects on stability or loading or discharging.
3) When ballasting at sea to counteract removal of cargo, due account should be taken off the adverse
initial effect of free surface on the vessel's stability.
4) If necessary remove a sufficient quantity of highest deck cargo first.
5) Minimize free surfaces by keeping the number of slack tanks to a minimum.
6) When liquid cargo is being discharged, due account should be taken of the FSE on the vessel‟s stability.
7) Load/discharge in such an order to maintain adequate trim and/or freeboard at all times.
8) When stowing deck cargo, adequate arrangements for drainage should be made between stowage racks
to the freeing ports.
9) Consideration should be given to the use of pipe plugs.
10) Allowance should be made in stability calculations for the entrapment of water.
11) In the calculation of the vessel‟s statical stability curve, use KN tables that have been “Corrected for
Free Trim”

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 12) When stabilizer tanks are in use, the free surface effects should be taken into account in stability
calculations.
13) The means of dumping the contents of such tanks in an emergency should be tested.
14) Where port and starboard cargo or service tanks are cross connected such connections should be closed
at sea.

Discuss the stability problems associated with the Towing vessels and
precautionary measures to improve the stability of such vessels.

1) All harbour tugs can experience very large athwartship forces when towing.
2) Such forces will often result in a large heeling moment which causes the vessel to heel over to a large
angle thereby reducing the vessel‟s dynamical stability.
3) This particularly the case when the towline is short and has low stretch characteristics.
4) Other factors affecting the stability include the dynamical forces during the towing operations induced
(eg., a sudden surge in the propulsion unit) and changes in trim caused by the pull on the tow line.
5) GIRTING:
a. A stability problem, particularly to conventional tugs, is the phenomena called
Girting
b. This is a sideways pull on the tug by the tow line when the ship is pulling away from
the tug, which is lying abeam to the direction of the pull.
c. The resultant heeling may be so large to capsize the vessel.

PRECAUTIONARY MEASURES:
1) Various aspects in the tug's design are usually incorporated to reduce the effect of heeling moment on
the overall stability of the vessel
2) These include giving the vessel a large beam/length ratio, increasing the freeboard, reducing the height
of the towing point, etc.,
3) The use of a long tow line with good shock-absorbing capabilities (high stretch) will help to reduce
sudden heeling moments caused by high peak forces in the towline.
4) The danger of girting can be minimized by the use of GOG rope (also known as GOB or BRIDLE).
5) This rope is used to hold the towline down at or near the stern of the tug which ensures that the tug is
brought into line with the direction of the pull and a capsizing moment is avoided.
6) Slowing down the large vessel will also reduce the danger of girting.
7) Such an action will also reduce the vessel‟s bow wave and therefore the heeling moment on any tug as
it takes a line under the bow.

A vessel's side compartment is flooded as a result of a collision. Describe the

countermeasures that may be taken in the event of such flooding.
Several measures can be taken in the case of damage and flooding, including:
1) Close all watertight doors.
2) Use of ship‟s pumps to remove water from the flooded compartment.
3) Take measures to restrict ingress of water (eg other vessels to stay in place initially and / or use of
collision patch.
4) Cross flooding – ballasting the other side of the vessel to bring the ship upright (movement of weights
may also be considered).
5) Ballasting aft also as to raise the forward section of the vessel or movement of weight to achieve a
similar effect. When combined with cross flooding this may result in the damaged area of the hull being
raised above the waterline.
6) Removal of weight, particularly from the upper parts of the vessel (eg empty swimming pool)
Transshipment of items of deadweight to other vessels may also be considered.
7) Shore up internally to prevent loss of adjacent compartment.
8) If all else fails consider beaching.
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Throughout the above, reference should be made to the stability data onboard guiding such circumstances.
Also, the SMS should be brought into operation. This usually involves informing ship owners of the situation
and gaining access to advice from experts associated with the Classification society and / or salvage
association.

TABLE OF CONTENTS :

| angle of loll | Carriage of timber | corrections tabular to assigned freeboar | critical instant dry
docking stability | damage stability | difference between type A and B | free trim wrt offshore supply
vessels | improvement of stability on roro ships | inclining experiment | load line rules | loadicator |
Loadline surveys | natural rolling period | passenger vessel flooding requirement | stability of offshore
supply vessel | stability on ro-ro ships | Statical stab curve derived fm KN values | stiff tender vessels |
still water rolling period | Stress and stability data | synchronous rolling | Type A Ships loadline rules |
Type B Ships loadline rules | upthrust | virtual loss of GM | windage |

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