|
Unfortunately, that formula is too simplistic for a trimaran. There are a least 3 reasons it won't work well for this boat.
First, with a trimaran, you normally have 2 hulls in the water. As the boat heals, the displacement of each hull changes. For example, if you are pushing reasonable hard on a close reach, you might have half of the boats weight supported by the ama (the outrigger). Thus, you could put a weight of 1350 in the calculator. If you do this (and still use 23.8 for the LWL) you get a speed of 12.3 -- considerably higher than what you get for when the boat is sitting flat with most of the displacement in the main hull.
Second, when you start talking about speeds in the low teens, the issue of planing rears its head. Subtle changes make big differences as a hull tries to plane. Dave Gerr makes this comment about his formula: "Keep in mind, though, that my rule describes the top hull speed that a hull MAY achieve without planing." If the hull starts to plane, then Dave's equation is not valid.
Third, in order for Dave's equation to be accurate, you must have a hull that has somewhat normal characteristics for its displacement. I'm not sure that either the ama or the main hull at a displacement of 1350 pounds have these "normal" characteristics.
In any case, speeds of 10 - 12 knots seem reasonable for this trimaran. I'm just saying that with a monohull, Dave's formula is probably very accurate, maybe to within 1/4 knot. With this unusual trimaran, the accuracy of the formula is more likely in the 2 knot range.
| 
This Mac 26X has NOT been photographically altered
-- Turol / Reynolds 21 -- 2/11/02 5:47p.m.
well-------- the workmanship looks decent.
-- Charlie Jones, Lindsey 21, Magnolia Beach, Tx -- 2/11/02 6:05p.m.
But it gets a lot more complicated for a trimaran. -- Roger, Potter 19, Seattle -- 2/12/02 3:09p.m.
