Dennis
Those plots I linked to yesterday give a clue to what I did. You cannot get the result straight out of Michlet. We know the wave interference is not large so the hulls can be treated independently.
If you consider the Proa ellipses for hulls a bit heavier than what you are doing you will see the ww hull goes from being heavily loaded at low speed to light loaded at high speed. It crosses a whole series of lengths for the minimum drag hull. So the length needs to reduce to remain a minimum drag hull despite the speed going up. Obviously there is a range of unloading due to the angle of apparent wind but for a fast boat in light breeze you will rarely have apparent wind aft of beam-on. So there is always some healing moment.
Lets say you look at four optimum hulls for the following conditions:
200kg at 4m/s
150kg at 5m/s
100kg at 6m/s
50kg at 7m/s
I know you will need to constrain the minimum length for the last case because planing would be best so it just goes really short. If you constrain to to minium of 4m say it will give you a beam and draft to work with. The speed range does not seem a lot but it is 3 times in force level from 4 to 7m/s.
After you have the four hulls you see how you can blend them into one hull. The one I produced was not very extreme. It did not morph much in length as it was unloaded.
It took me quite a while to produce those Minimum Resistance Hull charts and I did not go low enough to get lines where you need them for your mule. Extrapolating from what is there you see that a 200kg, 4m/s hull is going to be about 7 or 8m. By the time it is down to 50kg at 7m/s it should only have 4m in the water.
The lw hull loads as it goes faster and in the speed of interest constant length works well. The ww hull unloads as it goes faster and it needs to reduce waterline length and reduce the beam as it unloads to get the least drag hull. In practice with the little hull you can shift your weight but in a full size craft that will not alter much.
I should not the Minimum Resistance Hulls are almost circular section so if you constrain the section to get something for flat panel the optimum length and beams will both be a bit smaller.
Without actually building the VPP I cannot say what all this fiddling will achieve but the charts for the Minimum Resistance Hulls gives it some logic.
Rick
On 13/08/2010, at 10:49 PM, Dennis Cox wrote:
Rick,Godzilla is beating me to death. I've tried everything that I can think of. I've been trying to do trade studies using the current lee hull in combination with a box section with free dimensions. (beam, length, depth and seperation). Unfortunately, the heel angle is disabled in my version. Also, I haven't found a way to simulate the unloading/loading of the lee/windward hulls at speed.Anyway, I've been running analyses in the sub 10 knot range with both hulls. I'm assuming, I'll be flying the windward hull anytime over 10 knots... by hook or crook!Rocker - No matter what I do, I still get ZERO rocker designs in the windward hull. SO, what are you doing (analysis wise) to get the designs you have proposed to me?Dennis
Rick Willoughby
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