Dry Dock Stability

Question 1

When does P-Force occur?

Answer 1

It occurs when the vessel makes contact with the blocks in dry dock. It increases as more water is pumped out and the vessel pushes down onto the blocks

Question 2

What is P-Force?

Answer 2

A vertical force acting upwards through the keel proportionate to the buoyancy lost in dry docking once the keel touches the blocks

Question 3

At what moment will the maximum up-thrust occur?

Answer 3

At the maximum trim change, i.e. when the bow touches down on the blocks

Question 4

Define the Critical Period

Answer 4

This is the time after the stern touches down onto the blocks, while the water is being pumped out and the trim is changing

Question 5

Define the Critical Instant

Answer 5

The point where the vessel is most likely to capsize (the moment when the bow touches down onto the blocks)

Question 6

What is the formula for P-Force?

Answer 6

P-Force = (Change in trim x MCTC)/LCFfoap

Question 7

What is the formula for finding KG at the critical instant?

Answer 7

KG at CI = ((displacement x KGstart)/(displacement-P))

Question 8

If it is determined that the KG at the critical instant is going to be small, and the vessel will therefore be unstable at the critical instant, what two options are there to make the ship more stable?

Answer 8

1. Reduce the inital KG

2. Reduce the initial trim