Stability Flashcards
Define displacement
Amount of water displaced by a vessel afloat.
volume expressed in m^3
weight expressed in tonnes.
Weight x buoyancy
What is total buoyant volume?
Total volume from the keel to 1deck
What is reserve of buoyancy?
volume from the waterline to 1 deck
What is freeboard?
height from the waterline to 1 deck
proportional to reserve of buoyancy.
What is draught?
Height from waterline to keel
proportional to buoyancy volume.
What is centre of buoyancy?
point of upward thrust of the water on the ship’s hull.
What is the “ponding effect”?
free surface in a tank reduces when the tank is nearly full (95%) or almost empty. (5%)
leaves an almost solid weight ballasting down in the ship, creating stability.
What is minimum liquid loading restrictions?
preserves transverse stability by ensuring the centre of gravity does not rise too far.
stops metacentric height from going too low.
0.3m is the least for it to be safe.
What is the NSSC?
Naval Ship Safety Certificate
Certificate produced after an inclining experiment by the Naval Authority Group.
Lasts 10 years.
Condition, caused by and rectify LIST?
GM is positive when the ship is upright-stable condition
Caused by off-centre weight
Rectify by removing, centralise, counteract the weight add ballast tanks
Condition, caused by and rectify by LOLL?
GM is negative when the ship is upright - unstable condition
Caused by lack of ballast, excessive top weight, free surface effect, combination
Rectify by removing top weight, add low weight with water, reduce FSE
Name 5 information sources onboard?
Pumping and flooding board
Stability Computer
Carpet plots
Stability Information Book
Personal notes
How to use Levelling lines
with both tanks empty
both filled but not used
tanks filled with one used?
Valve left open for equal flooding into either tank
Valve locked and in ME Dep important key board
Valve locked shut but checked by watch keepers to keep level
Explain Heeling Motion (14mark question)
When the vessel is inclined by an external force such as wind or wave, the underwater volume changes.
The centre of buoyancy moves to a new position at the centroid of this new underwater volume.
The forces of gravity and buoyancy are now separated horizontally by a distance GZ (righting lever).
Weight and buoyancy remain equal and form a ‘couple’ producing the righting moment GZ.
What does a carpet plot assume?
Flooding all compartments between boundaries
Unrestricted vertical flooding
