Stability Flashcards
draw and label the internal hull
discribe displacement
the amount of water displaced by a vessel, measured in m^3
discribe buoyant volume
the volume of the entire watertight part of the hull. From keel to uppermost watertight deck
discribe reserve of buoyancy
the section of the hull that goes from the waterline to the uppermost watertight deck
describe freeboard
the height from the waterline to the uppermost watertight deck, measured from the side of the ship
discribe the centre of buoyancy
it is the point of action of the upward thrust of the water on the ships hull, this point is centroid of the underwater volume
name 4 methods to reduces free surfacing effect (fse)
- pump overboard
- longitudinal sub-division of compartment
- drain to lower, narrower, centreline compartment if possible
- fill the compartment up
discribe ponding effect
where tanks are filled to 95% to reduce free surfing effect
what is minimum liquid loading for
to preserve transverse stability by ensuring that the centre of gravity does not rise too far thereby reducing GM. GM is kept at a minimum of 0.3 m
what is NSSC
Naval ship safety certificate, produced after an inclining experiment by the NAG and last 10 years
draw and describe heeling motion
- when the vessel is inclined external forces such as wind or wave, the underwater volume changes shape
- centre of buoyancy moves to a new position at the new centroid of the new underwater volume
- forces of gravity and buoyancy are now separated horizontally by distance Gz
- weight and buoyancy remain equal and form a couple producing the righting movement, this brings the ship back upright
what condition does stiff require
larger GM GZ
more stable
shorter roll period
quick return to upright position
what conditions dose tender require
smaller gym/gz
less stable
longer roll period
slow to return upright
list some features of LIST
- GM is positive when upright
- steady roll
- caused by any off-centre weight
- little or no free surface
- heel towards the off- century weight or damage
how would you correct LIST
remove the off-centure weight
add an equivalent moment to the other side
transfer weight (fluids) from low side to high side
