Rick, "Keeping up is a long way short of 3X faster."
Please point to the boat that has a displacement hull speed of 40 knots.
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Hence Crouch's formula does not apply because it is intended for boats where drag associated with dynamic lift is significant.
There is no difference between dynamic and static lift, Physics 101 my dear sir.
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I think I see your problem. Yes, viscous drag increases with speed and surface area, but wave drag increases asymptotically. A displacement hull's drag is primarily determined by wavelength, not wetted surface. A superslick, laminar flow displacement hull actually has higher wavelength drag than a fouled hull, at hull speed.
Wave drag is negligible on a long slender hull. Viscous drag dominates. Negligible wave drag remains negligible at any speed. Viscous drag dominates. Crouch's formula is not applicable.
A displacement hull is dominated by wave drag, by definition. So from your above statement can I infer that you do not consider a Proa (long slender hull) to be a displacement hull? If you don't consider a Proa to be a displacement hull we don't have an argument.
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"No boat can be almost on plane at rest. Dynamic lift is a function of speed squared and AoA until the weight is fully supported by the dynamic forces. The statement is akin to saying a glider is almost flying while sitting in a hanger."
Many gliders are flying while tied down if there is a breeze : )
Not in a hanger as I specified.
Hmm, Let me try another approach. All lift is dynamic. You are being accelerated into the chair you are sitting on at 9.8 meters per second squared. Or conversely you are being accelerated by your chair at 9.8 meters per second squared. There is no difference in force whatsoever.
A boat hull pushing water down at 50 lbs a square foot is exactly the same as water pushing up on the boat hull at 50 lbs a square foot.
A glider sitting in a hanger is exactly displacing its weight, the same as when it is flying straight and level. There is no difference in the forces involved.
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Posted by: taladorwood@yahoo.com.au
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