455.
Righting Moment42 MIN
/
ΔG x GZ is known as the righting moment.
The righting moment is product of the weight of displacement and the
righting lever.
456. Righting Lever
GZ is the righting lever.
The righting lever is shortest distance between two parallel in the
direction of weight of displacement and the buoyancy.
G above M GZ = 0 G below M
457. Stability GM 3မျိးု
GM is the vertical distance between metacenter (M) and center of gravity
Positive GM
Center of Gravity (G) below metacenter (M)
When vessel heel, try to come back to lts original condition
Negative GM
Center of Gravity (G) above metacenter (M)
When vessel heel, vessel continue to heel further.
Neutral Equilibrium
Center of Gravity (G) and Metacenter (M) coincide.
When the vessel heel, neither try to neither return to original condition
nor heel further.
458. Free Surface Effect (loading LIST/ Other effect HEEL)
If a tank in vessel is partially filled with liquid.
The liquid free to move toward the side of heel of the vessel.
When the ship is incline.
This will cause shift of C.G and result is loss of G.M
Counter action
Not partially filled tank
Fitted wash bulkhead
Fitted longitudinal side girder
(c) Freeboard
A vertical distance from the summer load waterline to the top of the
freeboard deck plating, measured at the ship’s side amidships.
Load Line Marks
TF = Tropical zone load line in Fresh Water
F = summer freeboard in Fresh Water.
T = Tropical zone load line in Sea Water.
S = Summer load line in Sea Water
W = winter load line in Sea Water.
WNA = Winter North Atlantic load line
Fresh Water Allowance (FWA).
Fresh Water Allowance (FWA) is the difference in draught between sea
water load line (S) and freshwater load line (F).
When a ship move S.W to F.W without change in displacement.
There is a slight increase in draft, called Fresh Water Allowance
Fresh Water Allowance is used for computing the freeboard of ship
TPC= TONE PER CENTIMETER IMMERSION
What is Load Line Marking or အေ ကာင်း င်းြပပါ
Load Line Marks are located amidships on both side of the ship,
Showing maximum draught
to which the vessel may be loaded in summer and winter and in sea
water and fresh water
Purposes
Storage of cargo, ballast etc. is such as to get sufficient stability.
To avoid excessive structural stresses.
TF = Tropical zone load line in Fresh Water
F = summer freeboard in Fresh Water.
T = Tropical zone load line in Sea Water.
S = Summer load line in Sea Water
W = winter load line in Sea Water.
WNA = Winter North Atlantic load line
Purpose of free board
To ensure that, she cannot be loaded beyond her strength
To get enough reserve buoyancy.
To get enough structure and stability.
High enough working platform on the exposed deck
To get enough watertight from keel to freeboard deck and
weather-tight above this deck.
442. Type of Rudder
1. Unbalanced Rudder
Rudder with all of its area exist
Aft of the turning axis.
2. Semi-balanced Rudder
Rudder with all of its area of
Lass then 20% forward of the turning axis.
3. Balance Rudder
Rudder with all of its area of
25% ~ 30% forward of the turning axis.
What is 'keel of a ship?
Keel
The keel is back-bone of the ship.
It runs along the centerline of the bottom plating of the ship.
Types of keel
Bar keel
Flat plate keel
Duct keel
Bar keel
Flat plate keel
Duct keel
It consists of twin Centre girder and
Extends from the engine room length to the forward hold.
A width is not more than 2m.
It supported by stiffener
A watertight manhole door is provided at forward end of engine room as
an entrance.
To allows oil and water pipes to be carried beneath the hold spaces
To protected against cargo damage by leakage.
The ventilation fan and lighting are fitted in the duct keel for entering
+fitted trolley
438 Racking
When a ship Roll, the ship to distort transversely.
This is known as racking.
Resistance structures are beam knee,
Tank side bracket (or) margin bracket
Transverse bulkhead.
Panting and Stiffener
Panting is cause by water pressure fluctuations,
It create in and out movement of the shell plating, especially forward end
This In and out movement is called panting.
Resisting structures are beam, brackets, stringer plates etc.
Pounding
In heavy weather when the ship is heaving and pitching,
the fore end emerges from the water and re-enters in the water
with a slamming effect
This is called pounding.
Resist side frame, stringer, beam knee, beam, bracket, tank margin
bracket
Hogging sagging ြဖစ် မန်းဘယ်လိသိမလဲ
Forward draughtနဲ. Aft draughtနဲ marking ကေန ကည်မ့ ယ်
Hogging
When the wave crest is amidships, the buoyancy amidships is increased while
at the ends of the ship is reduced.
It is called hogging.
Sagging
When the wave trough lies amidships, the buoyancy amidships is reduced,
while at the ends of the ship is increased
It is called hogging.
440. Rise of Floor 47MIN
Ship hullမာ keyကေန ship side
Rise of bottom shell plating line above the base line.
The rise is measured at the line of moulded beam.
Rise of Floor is usually 150 mm.
It is purpose is to drain the liquid in DB tank
29.GM, 9 Ship and Tender Ship
437. Margin Plate 107 min MAR LINE
The outboard strake of inner bottom inclined 45˚
Connecting to bilge with shell plating
When the margin plate is turned down at bilge it forms the outboard
boundary of the double bottom, connecting the inner bottom in the
shell plating at the bilge.
It create a space for cargo bilge
Margin line 1.09
An imaginary line has drawn 75mm below the Bulkhead-deck (main
deck) at the ship side
It is the highest permissible location on the side of ship of any damage
It is the final condition of sinkage.
Two type of bulkheads
1. Water tight
2. Non Water tight
446 (a) Minimum numbers of bulkheads
The ship with aft machinery room requires minimum 3 numbers of
bulkhead.
They are collision bulkhead, forward machinery room bulkhead and
aft-peak bulkhead.
The ship with mid machinery room requires minimum 4 numbers of
bulkhead.
They are collision bulkhead, forward & aft machinery room
bulkhead, and aft-peak bhk
Construction of Collision bulkhead:
It is the foremost major watertight
bulkhead.
Collision bulkheads must extend to
upper deck.
It is located at a distance of L/20 from
forward perpendicular of ship. (L= Ship length)
It supported by stiffened
spaced about 600 mm
horizontal stringer also fit
+ Thickness of plating is increasing from the top to downwards.
Why Collision Bulkhead kept at L/20 of
By wave Theory", wave height from trough to crest is 1/20 of the wave
length,
maximum shearing force usually occurs at about L/20 of ship from each
end
For this reason, Collision Bulkhead is located at L/20 of the ship,
so that it is not so far forward, as to be damaged on impact. Neither should
it be too far aft, so that the
compartment flooded forward causes excessive trim bv hau.
