PowerPoint Presentation
SLAMMING &DECK WETNESS
SLAMMING In rough seas, the vessels bow and stern may
occasionally emerge from a wave and re-enter the wave with a heavy
impact or slam as the hull structure comes in contact with the
water. The vessel experiences impulse loads with high-pressure
peaks during the impact between the vessels hull and water
The Conditions leading to slamming are:High relative speed
between ship and waterSmall rise of floorShallow draft
Types of slamming1.Bottom Slamming The bottom slamming pressure
is to be calculated for the bottom structure in way of the flat of
bottom forward of 0.25L measured from the forward perpendicular
(FP).
2.Bowflare Slamming The Bowflare slamming pressure is to be
calculated for the side shell structure above the waterline in the
area forward of 0.25L from the FP.
3.Stern Slamming The stern slamming pressure is to be calculated
for the shell structure between 0.15L from the after perpendicular
(AP) and the aft end.
Effect of slamming1.The area between 10 to 25 per cent of the
length from the bow is the most likely to suffers high pressure on
bottom plating and sustain damage
2.Stress is developed along the main structure, called as
whipping stress. Due to that the deformation takes place in both
the vertical and the horizontal direction.
DECK WETNESSThe shipping of green water because of the Forward
deck relative motion to the wave surface is defined as deck
wetness.It is determined by the relative height of the deck above
the ocean surface i.e. the height of the freeboard
The Probability of increasing deck wetness is determined by two
methods.
STATIC SWELL-UPDYNAMIC SWELL-UP
STATIC SWELL-UPStatic swell-up of water at bow occurs due to two
phenomenon1.Bow wave generated by the vessel while moving in steel
water.2. Sinkage of the bow of the ship while running at a speed.
The effect of static swell-up is reduction of the freeboard
height.The effective freeboard is given by
Wheref(l)=Effective Freeboard.f(l)=Actual freeboard in still
water.hs(l)=Static swell-up.
(e)=Elevation due to bow wave. (s)=Sinkage due to speed.
f(l)=f(l)-hs(l)hs(l)=(e)-(s)
DYNAMIC SWELL-UPDynamic swell-up occurs because of the bow ,
while immersing pushes water aside and ,while emerging from below
sucks in water. The Dynamic swell-up is given by the following
expression.
Where, K=Constant depending up on the block-coefficient . =
1/3(CB-0.45) 0.6
