Numerical Seakeeping Analysist

[DunnX]

Hey mate, currently i working on a personal project about effect of chine with seakeeping performance. The boat that i gonna modified was the NPL hull, which are the experiment hull. but in the paper didn't give a LCG data. so how can i calculate the radius gyration of ship when there is no an LCG that known?

 

[TANSL]

Welcome to the forum.
When studying stability under various loading conditions, the initial metacentric height is calculated using the moment of inertia of the waterline area with respect to the corresponding axis passing through its CoG. This makes me think that the ship is being assumed to rotate around axes that pass through the CoG of the waterline, not the CoG of the ship.
I don't know if that can help you.

 

[jehardiman]

Asuming that the hull is sitting its lines and LCG=LCB; then the LCB of the NPL Hullform depends on the selected Block Coefficient with LCB locations being 8-10% aft of midships.

See this paper:
Bailey, D. (1976) The NPL High Speed Round Bilge Displacement Hull Series, Marine Technology Monograph, The Royal Institute of Naval Architects (RINA), Vol. 4.

 

[DunnX]

Welcome to the forum.
When studying stability under various loading conditions, the initial metacentric height is calculated using the moment of inertia of the waterline area with respect to the corresponding axis passing through its CoG. This makes me think that the ship is being assumed to rotate around axes that pass through the CoG of the waterline, not the CoG of the ship.
I don't know if that can help you.

Thanks mate

 

[DunnX]

Asuming that the hull is sitting its lines and LCG=LCB; then the LCB of the NPL Hullform depends on the selected Block Coefficient with LCB locations being 8-10% aft of midships.

See this paper:
Bailey, D. (1976) The NPL High Speed Round Bilge Displacement Hull Series, Marine Technology Monograph, The Royal Institute of Naval Architects (RINA), Vol. 4.

when assuming LCG = LCB, then what about the VCG? Thank you!

 

[jehardiman]

when assuming LCG = LCB, then what about the VCG? Thank you!

VCB comes from the lines at speed (i.e. with rise, squat, and pitch) as well as the need to determine hydrodynamic forces that support the hull. VCG you have to calculate based upon your design and the weights: hull, superstructure, propulsion, bunker, cargo, etc...