Preparations

SOLAS Requirements
 As per SOLAS-Chapter-1-Part-B-regulation-10, a cargo ship
structure, machinery and equipment including the outside of the
ship’s bottom and internals of the boilers to satisfy the minimum
requirements of SOLAS convention.
 A ship which complies with the required standards is issued with
Cargo Ship Safety Construction Certificate.
 As per SOLAS-Chapter-1-Part-B-Regulation-10- a minimum of
two inspections of outside of the ships bottom during any five
year period.
 SOLAS Requirements
 If the ship at the time when a certificates expires is not in a port
in which it is to be surveyed, the administration may extend the
period of validity of the certificate for the ship to complete its
voyage to the port of survey.
 The period of extension given under the above provision shall
not exceed 3 (three) months from the date of expiry of the
original certificate.
 For ships engaged in short voyages, the period of extension shall
not exceed 1 (one) month from the date of expiry of the existing
certificate.
 In any case as applicable above the interval between any two
inspections shall not exceed 36 months.
 SOLAS Requirements
 For a passenger ship the validity of the certificate shall not
be more than 12months from the date of existing certificate.
 For a cargo ship the validity of the certificate shall not be
more than 5 years from the date of existing certificate.
 SOLAS Requirements
 During the docking survey entire structural and other elements of the
hull which are not accessible for proper inspection when ship is afloat,
to be thoroughly inspected by surveyor of the recognised organisation.
 This includes maintenance of hull, propeller, rudder etc. and other parts
which are immersed in water and are normally inaccessible by ship staff
at normal sailing period.
 SOLAS Requirements
 An in water survey may be accepted in lieu of the intermediate survey.
 For vessels operating in fresh water special consideration may be
given.
 Apart from the above when vessel has suffered extensive damages to
the hull, it may be necessary to take the vessel to dry docks for repairs.
 In some cases the ship may have to be docked with full cargo on board
and in this case special care should be taken to prevent the excessive
load acting on the ship’s structure.
 In-water Surveys
 An In-water Survey may be accepted in lieu of the
intermediate docking between Special Surveys, an IWS
notation is assigned.
 This requires suitable underwater protection for the hull in part
taking the form of high resistance paint.
 This survey is to provide information normally obtained from
a docking survey.
 The In-water Survey is to be carried out at agreed geographical
locations under the surveillance of a class surveyor, with the
ship at a suitable draught in sheltered waters.
 The in-water visibility is to be good and the hull below the
waterline is to be clean.
 In-water Surveys
 The Surveyor is to be satisfied that the method of pictorial
presentation is satisfactory.
 There is to be good two-way communication between the
Surveyor and the appropriately qualified diver.
 Dry Dock File
 Preparation for dry dock begins after the ship sails from its
previous one.
 A dry-dock list of new items is created with specification sheets
describing individual jobs.
 A repair and survey specification covering overhaul of deck,
engine, electrical, navigation, communications and
accommodation equipment, repairs to hull plating hatch covers,
cargo gear, cleaning and painting approved alternations or
additions to vessels equipment etc.
 This specification is for items that would-be dealt with
concurrently with docking surveys and repairs.
 Dry Dock File
 These sheets are compiled into a dry dock file which some time before the
due date of the docking is submitted to several dry docks for pricing.
 The jobs are priced individually and as a whole.
 This allows the ship managers to streamline the jobs to provide maximum
value for money.
 The accuracy of the dry dock file is very essential for an effective planning
and pricing.
 Normally any repairs added during the docking will be priced separate and
in all cases are more than that is quoted for similar jobs in dry dock files.
 Dry Dock File
 Certain jobs are standard which are carried out in every dry docking.
 Certain jobs may require specialist attendance and may also require special
tools and spares.
 Scope of some jobs may broaden during the inspection and may require
inevitable deviation from the dry dock specifications.
 The accuracy of dimensions and specific materials requirements indicated in
the dry dock file will go a long way in maintaining the budget with in limit.
 The extend of dry dock occupancy depends on the jobs to be carried out in
the docks, so job file accuracy close to the reality will be helpful in
estimating various overheads during dry docking.
 Dry Dock File
 Again the provisions and bunker calculation requirements depends on
these factors, as it my be possible to procure these things from a place
where it is cheaper than in the place of dry docking.
 A good reference for preparing the dry dock file will be the previous dry
dock file.
 Chief engineer and second engineer are the key persons who are in
charge of preparing the dry dock repair files for the engine room and
deck machineries.
 Dry Dock File
 The dry dock file will be sent to office for approval.
 From the list repairs to be done by the ship staff and shore personnel will be
sorted.
 Approved list from head office will be sent back to the ship.
 Heads of departments to have copy of repair lists.
 Heads of departments to brief crew members regarding dry dock repairs.
 Safety committee also to be involved regarding dry dock repairs.
 The survey items will be enlisted separately.
 Any modification to be carried out will be specifically noted.
 Order the necessary stores, materials for repair jobs by ship's crew.
 Dry Dock File
 Ask to company for extra officer if deem necessary.
 Assign duties for officers and brief them about safety and security of
the vessel and maintaining efficient watch at all times.
 Information Required for Dry Dock Authority
 Apart from a detailed Dry Dock File, the following information are
to be given to the dry dock authorities before the ship reaches the
dry dock; such as:
 Length, beam, rise of floor, if any,
 Draughts and trim,
 Position of bilge keels and other appendages such as bulbous bow,
 Whether single screw or twin screw,
 The weight and disposition of any cargo onboard,
 Position of any hull damage for inspection or repair.
 The plan showing the position of bulkheads, main structural
members and drain plugs is required for the preparation of beds
and shores when dry docking in loaded condition.
 Three Requirements for Dry Dock
 Stability is the most important requirement for getting a ship safely
into a dry dock.
 The three important parameters which must be ensured before
entering the dry dock are:
 Adequate Initial G.M:
 When the ship touches the blocks, there is a reaction at the point of
contact which raises the centre of gravity “G” and reduces the
metacentric height “G.M” so that adequate initial metacentric height
is required to compensate for the same.
 To enhance the positive stability all slack tanks, and subsequent free
surface effects should either 'pressed up' or alternatively pumped out
if possible.
 Three Requirements for Dry Dock
 Vessel to be Upright:
 While entering the dock the vessel needs to be upright which
means there should be no port or starboard list when the ship
touches the blocks, the point of contact will be outside the
centre line of vessel, which may force the vessel to tip over.
 Small or Moderate Trim Aft:
 The slight trim allows the accenting of stern and bow in
tandem rather than simultaneously as it will reduce the load
and pressure on hull and the keel of vessel.
 Normally dry docks inform ship the required trim as a
percentage of LBP (e.g.0.9% of the LBP).
 Preparation for Entering the Docks
 The vessel must be prepared before entering the dry dock.
 Structural loading must be taken into account as the vessel is to
be point supported on blocks.
 A docking plan of the ships which shows such things as drain
plugs, sea boxes, underwater attachments, echo sounder
location etc is sent to the dry dock.
 Added to this are indications where hull repairs are required.
 This allows the dry dock ship managers to place the blocks on
which the vessel will sit.
 The vessel must be trimmed so as to be equal draught with zero
list.
 Preparation for Entering the Docks
 Special attention should be made when planning this for
any tanks whose contents may be varied due to repair or
housekeeping requirements.
 Also the engine room bilges should be cleaned and general
cleanliness of the engine room to be ensured before
entering to the docks.
 This is to prevent fire accidents during dry dock repairs.
 The total flooding system for the engine room and other
protected areas are to be secured and access is to be
controlled.
 The engine room work shop is to be well monitored as
outsiders also may use the facilities.
 Preparation for Entering the Docks
 All heavy weights secured prior to dry dock.
 All tanks and cofferdams must be sounded and recorded.
 Fire fighting plans and safety measures discussed before dry
dock
 Fire fighting equipment on board should be checked and
kept ready for use.
 Emergency lighting and generator should be tested before
entry.
 Escape routes must be clearly marked.
 Preparation for Entering the Docks
 All valves and chests to be overhauled must be clearly
marked.
 Shore connections for cooling water and fire line are to be
readied.
 On tankers all cargo tanks and adjacent spaces to be gas
freed.
 All the cargo pipelines and equipment to be thoroughly
flushed and gas freed.
 A gas free certificate is issued by the dock safety authority
before the ship enters the dry dock or even before starting the
layup jobs.
 Different Types of Docks
 There are two types of dry dock procedures:
 Graving docks.
 Floating docks.
 Graving dock is normally constructed on a land near the
coastal water with a rectangular solid concrete construction
with blocks, walls and gates.
 Vessel is shifted inside the dock and rested in the blocks.
 After the ship is in required position, gate is closed and water
is removed.
Different Types of Docks
Different Types of Docks
Different Types of Docks
 Different Types of Docks
 A floating dock is a “U” structure used in salvage, to carry
ship, which has met with an accident, from mid sea and which
is damaged and unable to sail further to go to a coastal dock.
 Several “U” type floating docks can be joined to carry a large
vessel.
 A valve is provided which can be opened to fill up the
chambers with water and which will make the dock immersed
in water so that the ship can sail out.
 The water is pumped out of the chamber which will allow the
dock to rise, exposing the underwater area of the ship for
maintenance or carrying the ship to repair facility.
 The Docking Process
 When it is decided that a ship is to enter the dry dock the first
thing that is done is the keel block arrangement.
 This is done by the Asst Dock Manager.
 The centre keel block arrangement is always the same.
 However, the rest of the keel blocks are arranged according to the
ships' structure.
 These are based on the ships construction drawings.
 Docking of any ship depends on the ship's draught.
 It is important to note the draught of the ship so as to estimate the
tide at which she should enter the dock.
 The Docking Process
 The draughts of container ships are usually 5-7m and for tankers
about 3m.
 When the ship is near the entrance of the dock, a crane is used to
lift wires to secure the ship to the dock winches.
 Two winches are secured at the aft end and two at the forward
end of the ship.
 These winches are used to guide the ship into the dock and bring
it to the exact spot at which it should be laid on the keel blocks.
 The central keel blocks will be arranged to support alternate
frame spaces compared to the previous docking keel plan.
 The Docking Process
 This is to ensure that the area where the keel block was placed in
the previous docking is attended.
 Once the ship is brought directly above the keel blocks on which
it will be laid on, divers are sent in the dock to ensure the ship
sits exactly on the keel blocks as the water is being pumped out
of the dock.
 The pump room located at the forward end of the dock controls
the rate of water being pumped out of the dock.
 This process can also be referred to as de-ballasting the dock.
 Once the ship sits properly on the keel blocks, fire hydrants,
safety signs and a shore gangway is attached to it.
 The Docking Process
 Safety personnel then inspect the ship and mark dangerous areas
on it with a Red tape.
 This is done so that hot work can be carried out with care.
 An example of such an area would be the fuel oil tanks.
 Application for all the necessary permits are then made.
 These permits include hot work permit, cold work and enclosed
space permits.
 Gas checks are also carried out in enclosed spaces every day to
ensure maximum safety.
 Stability During Dry Docking
 When a ship enters a drydock she must have a positive initial
GM, be upright, and trimmed slightly, usually by the stern.
 On entering the drydock the ship is lined up with her centre line
vertically over the centre line of the keel blocks and the shores
are placed loosely in position.
 The dock gates are then closed and pumping out commences.
 The rate of pumping is reduced as the ship's stern post nears the
blocks.
 When the stern lands on the blocks the shores are hardened up
commencing from aft and gradually working forward so that all
of the shores will be hardened up in position by the time the ship
takes the blocks overall.
 Stability During Dry Docking
 The rate of pumping is then increased to quickly empty the
dock.
 As the water level falls in the drydock there is no effect on the
ship's stability so long as the ship is completely waterborne,
but after the stern lands on the blocks the draft aft will
decrease and the trim will change by the head.
 This will continue until the ship takes the blocks overall
throughout her length, when the draft will then decrease
uniformly forward and aft.
 The interval of time between the stern post landing on the
blocks and the ship taking the blocks overall is referred to as
the critical period.
 Stability During Dry Docking
 During this period part of the weight of the ship is being borne
by the blocks, and this creates an up-thrust at the stern which
increases as the water level falls in the drydock.
 The up-thrust causes a virtual loss in metacentric height and it is
essential that positive effective metacentric height be maintained
throughout the critical period, or the ship will heel over and
perhaps slip off the blocks with disastrous results.
Stability During Dry Docking
Stability During
Dry Docking
 Stability During Dry Docking
 In the figure the longitudinal section of a ship during the critical period.
 `P' is the up-thrust at the stern and `l' is the distance of the centre of
flotation from aft.
 The trimming moment is given by the formula 𝑃 × 𝑙.
 But the trimming moment is also equal to 𝑀𝐶𝑇𝐶 × 𝐶ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑡𝑟𝑖𝑚.
 Stability During Dry Docking
 ∴ 𝑃𝑙 = 𝑀𝐶𝑇𝐶 × 𝑡
Or
𝑀𝐶𝑇𝐶×𝑡
𝑃= . Where P=Up-thrust in tonnes, t= change of trim in dry
𝑙
dock and l=distance of centre of flotation from stern.
 In the Dry Dock
 In many companies it is the responsibility of the ship staff to
inspect the hull of the ship on entering the graving dock.
 It is essential on such occasion to make a thorough examination to
ensure that all necessary work is carried out.
 The shell plating should be hosed with fresh water and brushed
down immediately to remove the salt before the sea water dries.
 The plating must be carefully checked for distortion, cracks on
welds, roughness, corrosion and slack rivets.
 The side shell maybe slightly damaged due to rubbing against
stays.
 In the Dry Dock
 After inspection and repairs the plating should be wire brushed and
painted.
 Any sacrificial anodes must be checked and replaced if
necessary, taking care not to paint over the surface.
 The ship side valve and cocks are examined, glands repacked and
greased.
 All external grids are examined for corrosion and freed from any
blockage.
 If service wastage has occurred the grid maybe built up with
welding.
 The shell boxes are wire brushed and painted with an anti-fouling
composition.
 In the Dry Dock
 If the double bottom tanks are to be cleaned, the tanks are drained
by unscrewing the plugs fitted at the after end of the tank.
 This allows for complete drainage since the ship lies at a slight
trim by the stern.
 It is essential that these plugs should be replaced before undocking
new gunmetal always is fitted.
 The after end must be examined with particular care.
 The propeller shaft is measured by inserting a wedge between the
shaft and the packing, for water lubricated stern tube type.
 If this wear down exceeds about 8mm the bearing material should
be renewed, 10mm being regarded as an absolute maximum.
 In the Dry Dock
 There should be little or no wear down on an oil lubrication stern
tube.
 The wear down in this type is usually measured by means of a
special gauge as the sealing ring is not allowing the insertion of
a wear down wedge.
 The efficiency and safety of the ship depends to a great extent on
the case taken in carrying out such an inspection.
 The anchor chain should be flashed out on the dock floor and
inspected.
 The chain should then be sand blasted and the ends changed over
before being pick up.
Rudder Wear Down Measurement In Dry Dock
 Dimension (1) must be substantially greater than
jump clearance (4) to protect steering gear from
damage in the event of grounding of skeg or
rudder.
 Dimension (2) should be sufficient to cater for wear
in carrier bearing and substantially greater than
riding washer clearance (5).
 Usually (1) and (2) are of the order 20 mm/25 mm
on a small/medium size vessel.
 If the riding washer clearance has reduced then the
carrier bearing is wearing or the skeg is set up.
 Ensure no drydock keel blocks in way of skeg.
 Always apply the wear limits given by the
manufacturer.
Propeller Shaft Clearances - Measurement
 Periodical docking surveys and periodical
propeller shaft surveys are incomplete without
propeller shaft clearances.
 These may be determined as bellows:
 When the shaft is removed for survey or
maintenance, by calibration of journals and
bearing bores.
 When bearing is exposed with shaft in place
for partial survey or seal maintenance, by
leveler gauges, or soft wood wedge driven
between shaft and bearing then measured
with calipers.
Propeller Shaft Clearances -
Measurement
 Before Flooding
 A check list should be made and verified before flooding the dock for
undocking the vessel.
 The list to include fit of bottom plugs, sea gratings, propeller ropes guard,
rudder, anodes, sea suction and discharges.
 Tank conditions checked and stability worked out for undocking draft and trim,
and to verify conditioned with dock master, the same condition as the vessel
went up on dock.
 After flooding dock to sea chest level, open and check sea suction valves for
any abnormality like leaky joints or packing.
 When sea water level covers the sea chest, each sea valve should be opened and
checked for any leakage.
 Before Flooding
 Purge air from cooling seawater pumps, run the pumps and check pressure.
 Test run the ship generators, until satisfactory, and cut out shore supply, cut in
ship generator, disconnect the shore connection, restart seawater pump,
record the time and read watt meter.
 All sea valves, shipside valves, repaired pipes, repaired jobs must be finally
checked, before leaving the dock.
 Prepare ME for manoeuvring.
 All DB tank soundings checked.
 Main engine crankshaft deflections are taken before and after docking to
check out any deviations from standard readings.
 Dry Docking with Full Cargo Onboard
 Followings things to be considered while docking with full cargo:
 Vessel is subjected to more severe stress and strains than normal dry dock.
 Uneven distribution of weight can induce severe stress concentrations.
 Additional weight of the vessel will make it difficult to achieve required draft
for entering.
 Following actions to be taken before entering:
 Press up the DB tanks beneath the holds.
 Distribute the weight of the cargo evenly over the inner bottom.
 Avoid local loading as much as possible.
 Dry Docking with Full Cargo Onboard
 Inform yard about cargo's characteristics, cargo plan and weight distribution in
respective holds.
 All cargoes onboard properly lashed, secured.
 Communicate with yard with respect to extra shores or keel/bilge blocks.
 Vessel upright, minimize free surface effect, adequate stability, trimmed as per
yard's requirement.
 Stand-by and prepare fire fighting equipments for repair and adjacent areas.
 Dry Docking with Full Cargo Onboard
 Procedures:
 Not possible for normal dry docking.
 Damage or repair works in a suitable position.
 Possible to pump out some of the dock water sufficient to expose the affected
area.
 Leave the vessel partly waterborne.
 Reduce the reactions on the blocks.
 Reduce the tendencies of hogging.
 Reduce the tendencies of sagging.
Bottom Survey route
 SURFACE PREPARATION
 Good surface preparation is essential to achieve optimum coating
performance.
 The main contributing factor of coating failure is poor surface
preparation.
 No paint system will give optimum performance over a poorly
prepared surface.
 If contaminants such as oil, grease, dirt, salts, chemicals, etc. are not
removed from the surface to be coated, adhesion will be
compromised, and/or osmotic blistering will occur.
SURFACE PREPARATION
 Loose rust left on the surface will cause a loosening of the coating and
eventual loss of adhesion.
 Also, good surface preparation roughens the surface to assist in obtaining the
proper surface profile, thereby promoting better coating performance in the
areas of adhesion, abrasion resistance, chemical and water resistance, as well
as the long term cosmetic appearance of the paint system.
 It is particularly important before painting new steel that any millscale should
be removed.
 Millscale is a thin layer of iron oxides which forms on the steel surface during
hot rolling of the plates and sections.
SURFACE PREPARATION
 Not only does the non-uniform millscale set up corrosion cells, but it may
also come away from the surface removing any paint film applied over it.
 Abrasive Blast Cleaning:
 There are generally three standards used for indicating the surface finish
such as:
 NACE = National Association of Corrosion Engineers
 SSPC = Steel Structures Painting Council
 Sa = Swedish Standard abrasive
 Of the above Swedish Sa standard is generally followed in the ship yards for
surface profile.
SURFACE PREPARATION
 Swedish Sa 3:
 White Metal Blast Cleaned Surface Finish.
 This blast standard is defined as a surface with a grey-white,
uniform metallic colour, slightly roughened to form a suitable
profile for coatings.
 This surface shall be free of all oil, grease, dirt, visible mill scale,
rust, corrosion products, oxides, paint, or any other foreign mater.
 This surface shall have a colour characteristic of the abrasive media
used.
 SURFACE PREPARATION
 Swedish Sa 2.5:
 Near White Blast Cleaned Surface Finish.
 This finish surface is defined as one from which all oil, grease, dirt,
mill scale, rust, corrosion products, oxides, paint or other foreign
matter have been removed except for very light shadows, very light
streaks, or slight discolorations.
 At least 95% of a surface shall have the appearance of a surface
blast cleaned to a white metal surface finish, and the remainder shall
be limited to the light discoloration mentioned above.
 SURFACE PREPARATION
 Swedish Sa 2:
 Commercial Blast Cleaned Surface Finish.
 This finish is defined as one from which all oil, grease, dirt, rust scale,
and foreign matter have been completely removed from the surface and
all (Sa 2 provides for almost all) rust, mill scale, and old paint have been
completely removed except for slight shadows, streaks, or discolorations.
 At least 67% of the surface area shall be free of all visible residues and
the remainder shall be limited to light discoloration, slight staining, or
light residues mentioned above.
SURFACE PREPARATION
 Swedish Sa 1:
 Brush Off Blast Cleaned Surface.
 This finish is defined as one from which oil, grease, dirt, rust scale, loose
mill scale, loose rust and loose paint or coatings are removed completely.
 But light mill scale and tightly adhered rust, paint, and coatings are
permitted to remain, provided they have been exposed to the abrasive blast
pattern sufficiently to expose numerous flecks of the underlying metal
fairly uniformly distributed over the entire surface.
PREPARATION OF HULL SURFACE
Vessel will be put in the dry dock
upon arrival in the shipyard.
The first step for the inspection
process is to conduct an
underwater assessment of the
fouling growth that has occurred
since the last inspection and
evaluate the coating condition.
This will be completed before
any hull cleaning is performed.
 PREPARATION OF HULL SURFACE
 Normally, ship hull can be divided into 6 quadrants as showed in
Figure.
 The six quadrants are:
1. Starboard forward,
2. Starboard aft,
3. Port aft,
4. Port forward,
5. Starboard waterline, and
6. Port waterline.
PREPARATION OF HULL SURFACE
 PREPARATION OF HULL SURFACE
 Fouling growth on the hull will be evaluated on a 0 – 5 scale.
 0 represents the optimal condition and 5 the worst condition.
 The paint maker’s inspector will record the fouling rating for each
quadrant and provide any additional observations or comments, such as
noting the type of fouling present on the hull surface.
PREPARATION OF HULL SURFACE
 PREPARATION OF HULL SURFACE
 Coating condition for the entire hull need to be evaluated based on
coating condition.
 The colour of undercoat also need to be recorded when the coating
was applied to the ship hull.
 Ratings of 1-3 represent antifouling painted surface appearance
associated with normal physical wear due to underwater cleaning
action or hydrodynamic effects.
 Ratings 4 and 5 indicate either excessive cleaning actions or
blistering due to internal failure of the paint system.
PREPARATION OF HULL SURFACE
 PREPARATION OF HULL SURFACE
 Hull cleaning
 There are various methods available for cleaning and preparing steel
surfaces prior to painting.
 The choice and methods of surface preparation would depend on the
location where the intended area of the vessel is required and the
availability of equipment to be used.
 Hull cleaning includes hard scrap and fresh water washing.
 Hard scraping shall be carried out to remove slimes, weeds, shells,
barnacles, etc.
 PREPARATION OF HULL SURFACE
 Besides that, approved detergents shall be used to remove any oil or
grease present on the hull.
 Hull cleaning standard by fresh water:
 Surface preparation by using fresh water can be divided into 4
levels.
 Table gives the levels or categories for fresh water surface
preparation.
 SALT TEST: The purpose of carrying out the salt test is to prevent
coating failure due to effects of salt elements on the surface before
coating.
PREPARATION OF HULL SURFACE
 In order to prevent the defect,
salt test is carried out to measure
the level of salt and to make sure
that salt content is at minimum
level.
 Normally, salt test is carried out
by using “Bresle kit sampler”.
PREPARATION OF HULL SURFACE
 PREPARATION OF HULL SURFACE
 Shipyard shall draw up a work schedule based on the agreed areas
and instruct the blasting contractor to proceed with the blasting
works.

 The blasting time of inspection is usually divided into two sessions,

once before noon and another late in the evening.

 This is to allow sufficient time for the blasters to produce a larger

blast area so that when the paint is mixed and applied, there will not
be much wastage for the coverage.
 PREPARATION OF HULL SURFACE
 GRIT BLASTING: Grit blasting is the commonly used method for
preparing a surface for the application of paint.

 When properly carried out, grit blasting can remove old paint, rust,
salts, fouling, etc., and provides a good mechanical key (blast
profile) for the new coating.

 Most shipyard prefers the 830 size grit in order to achieve a higher
blast profile on the steel substrate.
 PREPARATION OF HULL SURFACE
 It is important that the correct blast profile is achieved before the
substrate is coated.

 Paint manufacturers should specify the blast profile for each

coating.

 The instrument to measure the blast profile is called “Blast Profile

gauge” and the reading is in micron.

 In general, thicker coatings will require a profile with a greater peak

to trough measurement than a thin coating.
PREPARATION OF HULL SURFACE
 Blast profile: The correct blast profile is very important prior to
painting.

 If the blast profile is produced too high, an inadequate coating

coverage will result over any high and sharp peaks and this could
lead to premature coating breakdown.

 However, grit blasting can also result in an insufficient surface

profile and may simply re-distribute contamination over the steel
surface trapping contaminants under the surface.
 PAINT APPLICATION
 Airless Spray: Airless spray is now almost a universal method for
ship side paint application, where paint is atomised only with
pressure.

 The paint is pressurised to around 176-246 kg/cm2.

 Airless spray is the most efficient method for the application of

heavy-duty marine coatings, which allows the rapid application of
large volumes of paint as well as the application of high build
coatings without thinning.
 PAINT APPLICATION
 Airless spray method can reduce the overspray and bounce back
problems.

 The ships paints are formulated and manufactured to be suitable for

application by airless spraying.

 In Airless spray the paint is atomised by forcing the paint through a

precisely constructed nozzle, by hydraulic pressure.
 PAINT APPLICATION
 The nozzle hole diameter determines the film thickness applied per
pass of the spray gun.

 The nozzle should be selected in accordance with the coating

manufacturer’s guidelines.

 The speed of each pass and volume of solids in the paint will
influence film thickness.

 Airless spray equipment normally operates at very high pressures

and care should be taken periodically.
 PAINT APPLICATION
 One airless spray gun is capable of spraying between 50 and 80l/hr.,
i.e. covering 150 – 400 m2/hr at the required film thickness.

 Airless spray application produces less overspray than conventional

air-assisted spraying.
 PAINT APPLICATION
 Condition during application: There are some factors which must
be considered during paints application.

 The major factors are condition of substrate, temperature, relative

humidity, weather conditions and condensation.

 The proper ambient temperature for steel hull painting process

should be 3°C above dew point.

 Most paints can tolerate high humidity but condensation must not
form on the surface being painted.
 PAINT APPLICATION
 During the painting process for the ship hull, the relative humidity
must be below 85%.

 Furthermore, paint should not be applied during fog, mist or raining.

 Generally, under these conditions, it is difficult to maintain the steel

temperature above the dew point.

 Condensation should be avoided during painting process.

 Hull Steel Renewal
 The history of maritime accidents shows that, many of them
being due to structural failure.
 Failure is said to occur when the structure can no longer carry
out its intended function.
 The structural failures of old ships were predominantly due to
weakening of the structure due to lack of maintenance or
fatigue.
 Structural failures of young vessels were mainly attributed to
design fault combined with operational faults.
 Apart from the above structural failures are occurred on ships
due fire, collision, grounding etc,.
 Hull Steel Renewal
 So it can be seen that prevention of structural failures stems
from a combination of Good Design, Proper Maintenance and
Good Operating Practices.
 The first part is dealt by the naval architects while designing the
vessel.
 It is therefore important for naval architects to keep in mind the
various loads that a ship could be subjected to, in her entire
lifetime in the worst possible scenarios, when designing the
ship.
 This has become more optimised in the past with advent of
computer aided design concept.
 Hull Steel Renewal
 The three most important consideration made in this stage are;
 Action of sea
 Force acting on the heavy items composed of gravity forces and the
dynamic forces due to acceleration imparted by the ship's motion.
 Thrust due to main propulsion forces on the hull.
 Although most structural components are designed in such a
manner that if one element fails, it sheds its load on to another
element which can withstand this additional load, hence
normally this does not lead to an immediate catastrophe but
immediate remedial action is certainly necessary to prevent
further damage .
Hull Failure Statistics
Erika Disaster: Erika was the name of a tanker built in 1975 and
last chartered by Total-Fina-Elf. It sank off the coast of France
in 1999, causing a major environmental disaster
Prestige Disaster: The Prestige oil spill was an oil spill in Galicia
caused by the sinking of the oil tanker MV Prestige in 2002
MSC Napoli
MSC CARLA
 Hull Steel Renewal
 However there is a phenomenon known as the "domino" effect,
wherein the surrounding structural elements fail in succession
and the result can be loss of the ship.
 Even with advanced designs structural fractures are still
reported; however, some of these fractures can be attributed to
operational and mechanical failures rather than design and
construction failures.
 As shown in figure, weather, grounding, fire/explosion,
collision/contact and hull damage are the main causes of vessel
losses.
 So it is important that any structural failure noted are analysed,
repaired and reported religiously.
Hull failure Statistics
 Hull Steel Renewal
 There are three most important element to prevent structural
failure are;
 Regular inspection of the hull structure for corrosion,
fracture, deformation etc,.
 Evaluation of these defects and
 Rectification of these defects.
 If any of the above defects is noted during the inspection of the
hull, the nature of the defect and its location should be noted
for evaluation purposes.
 These details may indicate the potential cause of the defect and
determine the criticality.
 Hull Steel Renewal
 For example most of the fractures will be initiated from a
location where the stress concentration is maximum.
 Also most of the corrosion starts at the point where the stress
concentrations are maximum combines with other
environmental parameters.
 Stress concentration normally will be more on the ship’s
structure at the break of accommodation, shear strake, bilge
strake and the at the connection ends of bilge keels.
 Other parts of the ship’s structure may be subjected to high
stress values depending on the operating conditions like
concentrated loads, vibrations, wastage due to corrosion etc.
 Hull Steel Renewal
 At the evaluation phase, based on the information obtained
during the inspection, the following are to be given proper
consideration in order to determine the appropriate fracture
repairs to be carried out:
 Potential consequences of a found defect (or criticality of defect)
 Causes and nature of defect.
 Afterward, the team doing the examination would recommend
the action to be taken; temporary repair or permanent repair.
 In cases where temporary repair is considered, the team should
take into account the vessel’s intended route and service and
identify any potential risk.
 Structural Inspection
 As per the ESP the following terms are defined as given below:

 Close-up survey is a survey where the details of structural

components are within the close visual inspection range of the
surveyor, i.e. normally within reach of hand.

 Representative spaces are those which are expected to reflect the

condition of other spaces of similar type and service and with
similar corrosion prevention systems. When selecting
representative spaces account should be taken of the service and
repair history on board and identifiable critical and/or suspect
 Structural Inspection
 Suspect areas are locations showing substantial corrosion
and/or are considered by the surveyor to be prone to rapid
wastage.

 Substantial corrosion is an extent of corrosion such that

assessment of corrosion pattern indicates wastage in excess of
75% of allowable margins, but within acceptable limits.

 For ships built under the IACS Common Structural Rules,

substantial corrosion is an extent of corrosion such that the
assessment of the corrosion pattern indicates a gauged (or
Structural Inspection
Structural Inspection
EXCELLENT OVERALL CONDITION
EXCELLENT OVERALL CONDITION
GOOD OVERALL CONDITION
GOOD OVERALL CONDITION
Poor coating CONDITION
Structural Inspection
Critical Inspection Zones
Critical Inspection Zones
Critical Inspection Zones
General
Guidance
 Hull Steel Renewal
 When deciding the type of corrective to be taken, the
relationship between the size of a fracture and its impact on the
safety of the affected structure is often discussed.
 The extent of fracture may also determine the repair option that
is adequate to restore the ideal condition of the member.
 The type of repair technique to be performed as a fracture
solution depends solely on the cause of the fracture and the
necessity of immediate corrective action to restore the normal
operation, or even the strength of the vessel.
 The ultimate goal of a fracture repair is to eliminate the cause of
the fracture.
 Hull Steel Renewal
 However, there might be restrictions in fracture repair options
depending on the circumstances of when and where the
fracture was found.
 "Crop and renewal” and “gouge and re-weld” are the most
commonly used types of fracture repair.
 “Insert” is also commonly performed and is sometimes
considered as “crop and renewal” as it can be a full or partial
replacement of plate/panel of a structural section.
 In some cases, the repair work may not address the underlying
cause of the fracture and will eventually result in the same
fracture.
 Hull Steel Renewal
 The strengthening of a member through design modification
may shift the stress concentration to a nearby member which
can cause a new fracture.
 Repair work can be permanent or temporary.
 Permanent repair is carried out in order to comply with
Classification or Flag Administration requirements.
 Temporary repair is generally performed when permanent
repair cannot be carried out at the time of inspection due to
lack of appropriate facilities or skills.
 Repairs that are generally considered to be temporary include
cement patching, doubler plating and the application of drill
stops.
 Hull Steel Renewal
 For these types of repairs, the Flag Administration and
Classification Society must be informed and permission is
generally required prior to commencement of work.
 IACS has published various publications summarizing the
potential causes of structural failure and the associated
recommended repairs, often permanent repairs, which will
likely prevent the same problem from recurring.
 Following are a few notes of guidance on hull repairs as advised
by IACS.
 There is no need to recommend the renewal of an entire plate if
only part of it is damaged. But, the owner may elect to do so.
Hull Steel Renewal
 Individual small fractures in plates may usually be repaired
by veeing-out and re welding if the fracture is a simple one.
 If the fracture consists of several branches in one plate or is
of considerable length, say more than a third of the plate
width, the plate should preferably be renewed.
 Whenever possible, the origin of the failure should be sought
(such as by locating the point where the fracture-surface
chevrons point to, or come from).
 Hull Steel Renewal
Pitting Corrosion:
Pitting corrosion affects metals and alloys such as steel, iron,
aluminium and more.
The characteristic of this type of attack is that it is extremely
localized and the penetration is deep in relation to the area
attacked.
Pitting is one of the most dangerous forms of corrosion and often
occurs in places where it cannot be readily seen.
Pitting corrosion can be extremely intense on mill scaled steel left
outside.
Hull Steel Renewal
 Hull Steel Renewal
• The most common pitting corrosion causes are;
• Cracks in protective coating
• Scratches, scuffs & small chips
• Non-uniform stress
• Defective metal substrate
• Turbulent fluid flow
• Non-uniform protective coating
• Chemical attack on protective coating
Hull Steel Renewal
• Repair For Pitting Corrosion:
Pitting repair by plastic compound filler
material is only considered as a method to
prevent further corrosion and does not
contribute to the strength.
Hard coatings are normally to be applied
after repairs.
Hull Steel Renewal
For widely scattered pitting, i.e. intensity <
5%, and where the remaining thickness in
pitting is not less than 6 mm, the following
may apply:
The use of filler material/plastic compound
of a suitable elastic type according to the
manufacturer's instructions may be
acceptable provided:
pitting to be thoroughly cleaned (sand/grit
blasted) and dried prior to application
pitting to be completely filled
a top layer of coating to be applied.
Hull Steel Renewal
Welding, may be carried out afloat, in
accordance with the following:
pitting shall be thoroughly cleaned, ground and
dried prior to welding.
low hydrogen electrodes approved for the
material in question shall be used. Weld to start
outside pitting and direction reversed for each
layer.
For high intensity pitting and/or where the
remaining thickness is below the acceptable
limits plates/ stiffeners shall be renewed by
inserts.
Hull Steel Renewal
Grooving Corrosion:
Groove corrosion normally takes place adjacent to
welds and is of particular concern for the
connection of side frames to shell plate in single
skin bulk carriers.
However, grooving may be a problem for various
ship types. Other commonly affected areas are:
web frame connections to deck/stiffeners (ballast
tanks)
webs of side/deck longitudinals (ballast tanks) —
external shell plates in the forward part of the vessel.
Edge corrosion is mainly found around cutouts in
web structures and at the free edges of flat bar
deck longitudinals.
Hull Steel Renewal
The following assumptions apply:
grooves and edges are smooth and without sharp
edges or notches
welding is intact and with acceptable remaining throat
thickness
“accumulated transverse grooves” means the total
length of all grooves at each structural member in deck,
bottom, longitudinal bulkhead or side plating within
the cargo area of the ship.
• If any of the above conditions do not apply then
renewal will recommended.
Hull Steel Renewal
The maximum extent of grooving and the
acceptable minimum thickness of stiffeners and
plates may be taken as follows:
Where the groove breadth is a maximum of 15% of the
web height, but not more than 100 mm, the remaining
allowable thickness in the grooved area may be taken
as,
tmin = 0.7 · torig
tmin = 0.75 · torig for L-profiles, but not less than 6.0 mm.
Accumulated transverse grooves in deck, bottom,
longitudinal bulkhead or side plating within the
cargo area is normally limited to 20% of the
breadth respective height of the ship.
For ships with large deck openings, such as
container ships, the accumulated length of
transverse grooves in the passageway is normally
limited to 10% of the breadth.
Hull Steel Renewal
Corroded welded seams in shell plating Minimum
thickness at the weld or plate: tmin = 0.7 · torig
Accumulated transverse grooves in bottom and
side plating within the cargo area is normally
limited to 20% of the breadth respective height of
the ship.
Hull Steel Renewal
Edge corrosion:
Flat bar deck longitudinals:
For acceptable extent of corrosion of the free
edge of the longitudinals the following may be
applied:
the overall height of the corroded part of the
edge is less than 25% of the stiffener web
height,
the edge thickness is not less than 1/3 torig and
well rounded
the thickness of the remaining part of the
longitudinal is above the minimum allowable as
per the class requirements.
Hull Steel Renewal
Manholes, lightening holes, etc.:
Plate edges at openings for manholes, lightening
holes, etc. may be reduced below the minimum
thickness as described below:
The maximum extent of the reduced plate thickness,
below the minimum as per the class rules as
applicable, from the opening edge shall not be more
than 20% of the smallest dimension of the opening
but should not exceed 100 mm,
Rough or uneven edges may be cropped-back
provided the maximum dimension of the opening is
not increased by more than 10%. Special care shall
be taken in areas with high shear stresses, including
areas with adjacent cut-outs.
Hull Steel Renewal
Repair:
Where excessive edge corrosion is found, renewal
by inserts will normally be required.
However, alternative repairs may be considered
as follows:
Edges of openings maybe reinforced by:
compensation reinforcement ring with lap joint
additional flanges
possible closing of openings by collar plates around
stiffener and at corner cutouts adjacent to the
affected areas to be considered.
Re-welding of grooves and corroded butts or
seams:
the surfaces shall be cleaned, ground and dried
before welding
low hydrogen electrodes to be used.