Dennis
I have been looking at some logic behind the selection of hull parameters.
I have set up three charts that give the length, beam and draft of the minimum resistance hull for particular displacement and speed.
The speed is given in m/s so double to get knots. The displacement is in cu.m.
I have looked at how they might be used for selection of hulls for various configurations of sailing craft for a 2 tonne boat with a target speed of 10m/s. The full operating range of the hulls is shown as shaded squares and there are ellipses which show the range of most interest for the respective hulls.
Here is the Proa:
http://www.rickwill.bigpondhosting.com/proa.png
It is clear that for a 2t boat you would be looking at about an 18m long lw hull with a fixed beam around 0.6m and the draft ranging from 0.25m to 0.3m as it loads. For the ww hull you would like the length to reduce as it unloads, the beam to get less and draft will naturally reduce.
I have also done a cat and you can see that it is much harder to optimise the hulls because they both have to do two jobs:
http://www.rickwill.bigpondhosting.com/cat.png
You can begin to understand why rocker might have an advantage in a cat hull so the length reduces as the hull unloads but then holds the length when loaded beyond the static line. You would probably settle on 14 to 15m if you want a good average. The beam would ideally hold around 0.6m above the static waterline and reduced to nothing as it unloads. The draft will be what it will be given the other two.
The tri hulls have to cover even a wider range than the cat:
http://www.rickwill.bigpondhosting.com/tri.png
The selection of hulls will really depend on where you want to aim the design. For high performance you would put the length in to the amas and probably accept a shorter main hull.
The curves do not go down into low enough displacement to be useful for your test hull but you can see that the 8 to 9m you settled on fits the lower displacement end of the chart.
If nothing else it shows the significance of the proa configuration in achieving something approaching the optimum sailing craft. I know most here realise this but it is not widely known as far as I can tell.
Rick
