5003 Lectures - Faculty of Engineering and Applied Science

E5003 - Ship Structures I 54
© C.G. Daley
1.1 L Wave
L/20 waves have been found to be too conservative for large vessels, esp. for vessels
>500 ft. A more modern version of the 1 . 1 L wave. In this case;
as before, LW = LBP
H w
or
= 1.
1 L BP (in feet)
H = 0.
607 L (in meters)
w
BP
For trochoidal waves this gives;
L BP
R = , r = . 55 L (feet) or BP
r = . 303 L (meters)
BP
2π
Calculating Wave Bending Moments
We can now calculate the wave bending moments by placing the ship on the design
wave. We can use the bonjean curves to determine the buoyancy forces due to the
quasi-static effects of the wave;
The steps to determine the wave bending moment are;
1. Obtain bonjeans
2. at each station determine the still water buoyancy forces, using the design
draft. Fisw = Aisw li ρg
3. at each station determine the total buoyancy forces, using the local draft in
that portion of the wave. Fiwt = Aiwt li ρg
4. The net wave buoyancy forces are the difference between wave and still
water. Fiwave=Fiwt-Fisw