Longitudinal Stability Flashcards
Define Trim
The difference between fore and aft draft named by the greater.
Define Centre of Flotation
Geometric centre of water plane area.
What is the draft at the COF
True Mean draft (the draft to use with hydrostatic particulars).
Does the draft at the COF change when weights are shifted?
The draft at the COF does not change. The trim will ∴ the draughts fore and aft will.
Define LCF
Longitudinal centre of flotation, a distance from the AP to the COF.
Define LCG
Longitudinal centre of gravity, a distance from the AP to the COG.
Define LCB
Longitudinal centre of buoyancy, a distance from the AP to centre of buoyancy.
How do we obtain the LCG
LCG = ∑moments about AP / displacement
Sketch and label a longitudinal section of a vessel, trimmed by the stern
Describe the correlation between LCG, LCB, trim.
LCG < LCB = vessel trimmed by stern
LCG > LCB = Vessel trimmed by head
LCG = LCB = vessel even keel
When a vessel is required to be at a certain trim. How do you calculate for the amount of weight to be shifted or the distance for a weight to be shifted?
RQD COT = Trimming Moment / MCTC
RQD COT = (Current trim +/- RQD trim, if same sign then ‘-‘ if opposite then ‘+’)
Trimming MOM. = (w x s)
Transpose formula to get W or S
How do you determine the initial condition if the vessel is in SW?
Use the SW column
How do you determine the initial condition if the vessel is in FW?
Use the FW column
How do you determine the initial condition if the vessel is in DW?
The vessel is somewhere between FW and SW.
△ = ▽ x 𝜌 (FW is ▽ of △)
A vessel is going from SW to DW. How would this effect the calculation?
- ▽ = △ / 𝜌
- Divide the displacement by the density to give a volume of displacement. Then use FW column when finding data and apply DW corr. as required.
