You need to specify the target speed as well, but assuming 25kts, the lowest drag hull will be very short and designed to plane. The drag for an optimised planing hull at a guess will be around 800N.
Constraining the length to > 12m produces a hull requiring 990N to do 25kts. The hull has a lot of rocker and will generate wave making lift as well as significant planing force if flat bottomed with rocker.
This is really getting into planing regime rather than displacement and analysis without account for the dynamic lift would not be realistic for 500kg at 25kts on a flat bottom.
Dropping the design speed to 14kts for a 500kg hull gives the lowest drag hull of 11m. Drag at 14kts is 380N. Interestingly drag at 25kts is 987N so about the same as the 12m.
It takes a lot more effort to actually analyse the trim but I would be surprised if you could not get it to maintain level trim while in displacement mode up to 14kts. After that the planing forces come into play and if it has some rocker the nose lift should overpower the sail moment in the same way you see with a sailing dinghy when on the plane.
So the 500kg hull to go fast creates an interesting dilemma. Do you want to go reasonably short and aim to plane or do you want to keep long and slender to achieve wave piercing. It also brings to question what the best shape of an unloaded ww hull might look like at a particular design speed.
Rick
On 16/07/2010, at 1:25 PM, tsstproa wrote:
What if the same 12m. hull was only 1/2 tonne displacement?
Todd
--- In harryproa@yahoogroups.com.au , Rick Willoughby <rickwill@...> wrote:
>
> The length constraint or non-constraint is a function of design speed
> and weight.
>
> As an example a 1 tonne hull with a flat bottom designed for minimum
> drag at 25 knots results in a length of 12m. However this hull will
> not generate enough bow up moment through wave making to counter the
> moment from the rig to drive it at that speed. Extending the length
> to 15m will get close.
>
Rick Willoughby
03 9796 2415
0419 104 821
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