Vpp heel resistance

Larsson & Eliasson p83, Heel resistance;

"One way to obtain this component would be to compute
the hull parameters for the heeled hull and use in the
formula above. (delft) By comparing with the unheeled
results the effect of heel could be obtained.
However, if this technique were to be used, there is
no need to treat the heeled resistance as a separate
component."

Any ideas on how vpp make this estimation? I noticed they do not require lcg or cp at heel angles, even though these can change with heel, and the effect of asymmetry, beam/draft ratio?

 

Heel drag is a function of change in wetted surface and waterplane symmetry?

Is there usually more with heel?

 

I suspect most systems use the added heel resistance method that may be described in Larsson's book, otherwise is available on the web at the HISWA site. This is, however, rather innacurate if the hull in question deviates much from the parent hull.

It is much better to calculate the wave drag and skin friction drag in the heeled condition. Both elements of the drag will change, perhaps quite considerably, because of the assymetry of the heeled hull. One really needs to use CFD with a free surface or tank testing to obtain a resistance, and neither of those are trivial.

The other thing that will change (because heel induces pitch and yaw) will be the angle of the appendages to the flow, and thus the appendage drag will also change. The dynamic hull condition (in flat water), though may not be the same as the hydrostatic condition, due to the pressure distribution.

Dependant on how good an answer you want it can become quite a complex problem.

Tim B.