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Old 09-20-2012
bobperry bobperry is offline
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Re: Moment curves

Hey, I resemble that remark.

What I don't understand is:
Exactly why there are moments above and below that centerline.
What I am thinking is that some immersed sections have immersed areas on both sides of the actual yachts centerline while immersed areas in the ends only have the immersed area outboard of the centerline. That makes sense to me. I'm not sure what it means but I'm pretty sure that's what I am seeing. I'll go back and stare at it some more. I'm kind of slow so I need time to digest this and then I can give you the "immersed area moments for dummies" explanation.

No, I don't like my explanation. I'll call BS on myself.

It says that the areas above the line are to windward and the areas below the line are to leeward.
Ok, but when you heel there are no immersed areas to windward in the ends, the windward side omes out of the water. It can't be immersed.

Maybe that's what it is showing. The only immersed areas contributing to stability are in the middle of the boat and the areas in the ends don't add anything at all. This is something you do not want to generalize about. But in boats with elevated counters and bow overhangs I have said all along that they don't immerse enough volume to contribute to stability or sailing length.
That always makes lovers of traditional boats mad and maybe I am just seeing what I want to see. The problem with my latest explanation is that according to the graphs there is nothing in the ends that contributes to stability. That's not right either. If there is any immersed area
(area times a distance equals volume) to leeward at all and I suspect there would be, although small, then it should show up on the leeward side of the graph.

I'll stare at it some more. I know in time I can get a handle on this.
"Moment" in this case is an immersed area times a distance from some reference point. I think the reference point is the actual centerline of the boat in this case.
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Last edited by bobperry; 09-20-2012 at 12:33 PM.
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