Rick, " There is essentially no wave drag or induced drag associated with dynamic lift. It is all viscous drag."
Dynamic lift can and does produce huge wave and drag forces. You just don't see them and the vertical wave is so much longer than the horizontal waves that there is almost no wavelength limit.
Why do you think Subs are four times faster than surface displacement vessels?
"That is why there is a specific shape for a displacement hull that gives minimum resistance for a particular speed and displacement. A slender hull has lower wave drag but more viscous drag than a wider hull while the wider hull has more wave drag and less viscous drag than the slender."
You are making my point that wave drag and AOA are bigger drags than viscous drag.
"A simple example - two hulls of rectangular section with draft half of beam so same section shape.
Short hull 2m long 2m beam 1m draft gives volume of 4Cu.m and wetted surface of 12sq.m
Long hull 16m long 0.5m beam and 0.25m draft volume of 4 Cu.m and wetted surface of 16.25sq.m
Viscous drag on the longer hull is 35% higher - certainly not trivial."
An elliptical shape has less wetted surface than either, and a round shape has the greatest drag of all (except a flat plate moving perpendicularly). That is why you have to compare similar shapes.
But back to your example, what is important is the flat plate drag or frontal area. In your first example the frontal (and rear) area is 4 square meters and in your second example the frontal (and rear) area is .25 square meters. With the same surface finish, everyone knows which shape is faster and has less drag.
The long slender shape is almost on plane at rest. If it is actually on the surface it really is on plane. That is why weight is so important with the HarryProa.
A curved underwater hull decreases wetted area and viscous drag, but increases wave formation and has much higher drag.
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Posted by: taladorwood@yahoo.com.au
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