hull model testing

[wardd]

i was thinking weights and balance and loading and to get an idea of how it would behave , rolling etc?

[Leo Lazauskas]

Originally Posted by ancient kayaker

Is it practical to determine the skin-friction separately by performing a fully immersed (submerged) test then adjusting the surface results to isolate the wave resistance, since they scale differently?

If so, then the effect of the support structure can be eliminated from a submerged test by weighting a model to float stem up and releasing it at the bottom of a tall tank, noting it's speed at different bouyancies. The effect of the submerged deck can be removed by cutting off the top of model at the waterline and attaching a duplicate to it as a mirror image.

It's probably not a good method because (among others):
1. You wont get the same type of separation near the stern, and you might get unusual flow separation at the bow. Hence there might be some very odd form drag effects.
2. Skin-friction depends mostly on the wetted surface area.
3. There are some interactions between the waves on the hull and the boundary layer for surface-piercing vessels, so skin-friction is not exactly proportional to surface area. Remember: it's Froude's "Hypothesis", not Froude's "Law
"

The idea of a double body is used in some analytical treatments (albeit in a different way), so your proposal is not a completely silly idea.

Leo.