I think this design might be the fastest of all proas. It has the weight of both the ackommodation and the sailing rig to windward (heavy short hull), giving a good righting moment. It sails with the longest hull to leeward, meaning low drag (light long hull) |
This is the part I have tried to get weight to windward proa advocates to assess in technical terms because it is simply an incorrect blanket statement and ignores rear world displacement changes from the short to the long hull.
We know the following: Displacement to length ratio is the overriding factor when it comes to hull resistance at higher froude numbers. Therefore a long light hull will have low drag compared to shorter heavier hull.
This kind of proa has a long light hull, BUT the majority of the displacement is on the short heavy hull. Since we know resistance is related to DLR it makes sense to gauge performance on the most substantial hull which is the short heavy hull. Think of it this way if I put a light 50 foot outrigger on a 25 foot Bruce Roberts Spray will it suddenly have an amazing DLR? Of course not.
Now obviously the weight to windward proa has a TOP speed advantage as when all its righting moment it used up and sailing 100% on its long hull its DLR can be considered on its long hull. But on every other occasion the overall resistance will be some combination of the DLR from the more substantial short hull combined with the long hull. Sailing in light winds, motoring, sailing downwind etc.
Therefore this configuration is not automatically fastest and depends greatly on its operating condition.
IMO these are facts which are hard to dispute. I am certainly not part of any tribal proa bashing brigade. I think Epicure is awesome. I am a big fan of these designs and their many other advantages but I would like to see this fact discussed within this type of boat rather than ignored. A boat like Bucket list easily has the sail area and light weight to be able to use its long hull fully most of the time. For a larger cruiser this will not be the case. I wish I knew how to use Michlete so I could simulate total resistance of a proa as the displacement shifts from the short hull to the long one. If tests like this have been done I would like to see the results and how they relate with hull loading changes from sailing loads at various wind strengths and directions.