Bulbous Bow Cb

[nmfb105]

Hi

Just wondering how you define a ships Cb when a bulbous bow is involved.

Cb is usually defined as

Cb = V/ (Lwl x Bwl x T)

[Volume over Waterline length by Waterline Breadth by Draft]

However with a bulbous bow involved your waterline length is shorter than you immersed waterline, hence you have some displacement volume outside of your defined waterline block.

so my question is from what length point do you define your "Block" witha bulbous bow?

Any help or info appreciated
Cheers

Nick

[Ad Hoc]

Volume is volume.

What do you think the volume is for the Cb, for a dreadnought destroyer, or a SWATH!!??

The term 'block' in these instances is bit of a misnomer.

[jehardiman]

As Ad Hoc said, volume is volume.

Traditionally, a bulb is an appendage, and like rudders and bilge keels is not considered part of the main hull for the volumetric coefficients. So the Cb is defined in the traditional way with the LwL measured from the Fwd Perpendicular, which is placed at the Design Load Waterline, and at this draft the bulb should be submerged. If it isn't submerged, it isn't functioning as a bulb bow.

FWIW, I doubt that the additional volume of a traditional bulb bow will change the block more than 0.005. If it does, then it is not a bulb, but part of the main hull.