The low wave drag on a slender hull comes at quite a cost in terms of increased wetted surface. That is why meticulous attention needs to be taken with the surface finish. There is essentially no wave drag or induced drag associated with dynamic lift. It is all viscous drag.
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.
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.
On 20/03/2015, at 3:19 PM, "taladorwood@yahoo.com.au [harryproa]" <harryproa@yahoogroups.com.au> wrote:
But the wetted area of a long thin hull is the same as a short fat hull if they are the same basic shape, flat, elliptical, or V etc.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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