Re: : Re: : Re: [harryproa] Re:: Lucs Proa

I have set a criteria for the hull as being minimum drag shape for 1100kg at 8kts. That produces a hull with primarily convex surfaces. The best hull has a small transom so I took the front half and mirrored it. I then produced drag curves for various displacements. Eventually this data can be used in a VPP.

This particular hull has flat bottom that is 500 wide at the middle. The sides are very slightly flared such that the beam at 600 above the keel is 550. The sides are not parallel so could not have a folded chine.

If you want a hull having a folded chine then I can make something similar and compare. The included angle at the stem usually has significant influence on drag. In the past I have found that stubby bows increase wave drag quite a lot. For a beam of 500 the bow wedge needs to be at least 2m. That makes the half angle less than 7 degrees.

At 20knots the dynamic lift is around 130kg when the foot of the stem is on the surface. You could get more lift if it pitches up more but that would likely require shifting weight aft. In any case there is very little reduction in drag associated with planing when this hull is unloaded by the healing moment.

One question from this is how do you plan to build the hull? It is usually worth the effort to see if there is any drag penalty for simplifying the shape to make it easier to build.

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On 06/05/2016, at 3:06 PM, lucsimard@ymail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:

Hi Rick,

I am getting at the ww hull now and trying to figure what would be the best to begin with. I would really appreciate your insights if you could!

Hull will be 11 m long and displacing 1300 kg at maximum load. It is now 400 mm wide and my simple arc sided shape gives a bottom area of 3.4 sqm. I could make the hull narrower or wider, it is not really a problem.

Since this hull is lifting as soon as the wind picks up, I guess it should be designed for best efficiency in light air, but then again I want it to have the best dynamic lift so it's drag is reduced as soon as possible, so flat bottom with rocker. It now have 200 mm rocker starting about 3 m form the end.

Any idea what a good starting point would be ?

Thanks a lot,
Luc