Mateo
Not really applicable to a harryproa. The design speed on the Twin-8 is 3.3m/s with design displacement of 180kg. An 18m proa lw hull would be optimised for somewhere between 16 to 20kts in displacement mode then the flat bottom gives it potential to gain from dynamic lift above that. The keel is essentially straight with rocker in the ends. The rocker with a flat bottom helps to get the nose up.
Minimum drag displacement hull for 10m/s (say 20kts) displacing 3 tonnes has a LWL 19.3m and BWL of 790mm. There is a some concavity in the waterline toward the stern but buttocks are convex; although I am only viewing offsets as the optimisation runs. It also has a small transom. So the lowest drag double ender may be a little longer. Drag is 2.14kN. And that is only one hull. I have assumed the ww hull is carrying 1 tonne in a total displacement of 4 tonne under sail.
Rick
On 27/03/2015, at 4:12 PM, "mateo002@yahoo.ca [harryproa]" <harryproa@yahoogroups.com.au> wrote:
Rick,
ok thanks for the further illumination. After staring at the original pic longer I did start to see the slight indents. I guess the combination of concavities at both ends attaching to the bottom flat section has a net result of upward lift instead of downward drag. Very interesting.
Is it applicable to a 18m Harryproa?
Mateo
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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