Thread: Rule of thumb for wetted surface area
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Anonymous Anonymous is offline
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First recorded activity by BoatBanter: Dec 2006
Posts: 7
Default Rule of thumb for wetted surface area
wrote:
Anonymous wrote:
Does anyone know the rule of thumb for wetted surface area? If the hull
stays exactly the same same size and form yet the wetted surface area is
increased in what proportion does the speed decrease for a fixed power
input?


There is no simple "rule of thumb" for this. How do you increase
surface area and keep hull size & form the same? Is displacement held
constant? Have you already factored out wave-making drag?

(signed) Injun Ear (formerly known as Eagle Eye)


I'm asking about rate of change, not absolute numbers so the assumption
of not changing the surface area and hull form is valid. It's an element
of calculus if you have studied mathematics. To give a realistic
example, change the hull from smooth to one of those lapstrake types.
Leave out drag and reread the first three words of the title: "Rule of
Thumb".