Anon asked:

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?


You answered:
If you want to know what the rate of change will look like, it will
increase geometrically with the initial velocity.


Gilligan wrote:
The actual answer is that the speed decreases as the square root of the
wetted surface. This is less than a linear increase and certainly not
"geometric" in its common usage.

Sorry, that wasn't too clear. The -rate of change- will vary
geometrically, not the decrease in speed.



Interestingly the hull speed formula varies as the square root of the LWL.
Perhaps there is a relationship that disregards displacement or hull shape.

Perhaps, but perhaps not. The hull speed formula is rather basic and
does not give precise results. Or would you seriously suggest that hull
shape, displacement, cross sectional area, etc etc, don't matter in the
slightest and that LWL is the only determinant for speed/drag ratios?

signed- Injun Ear (formerly known as Eagle Eye)