5003 Lectures - Faculty of Engineering and Applied Science

E5003 - Ship Structures I 52
© C.G. Daley
or much longer than the vessel, the bending moments will be less than if the
wavelength equals the ship length.
Consequently, the design wave for any vessel will have a wavelength equal to the
vessel length. The wave height is also constrained. Waves will have a limited height
to length ratio, or they will break. This results in a standard design wave of L/20. In
other words the wave height (peak to trough) is 1/20 th of the wave length.
Trochoidal Wave Profile
Note that the waves sketched above did not look like sinusoids. Waves at sea tend
to be trochoidal shaped, rather than simple sine waves. This has the feature that
the crests are steeper and the troughs are more rounded.
A trochoidal wave is constructed using a rolling wheel.
In the case of the design wave;
LW = LBP
HW = LBP/20
We can see that;
LW = 2 π R
HW = 2 r
}
for now we assume that this length and
height or wave is possible