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From: Tom MacNaughton
Date: 23 Dec 2007
Time: 14:43:08 -0500
Remote Name: 66.252.35.203
I’m find it difficult to answer the question you ask in your first sentence in that I don’t know what type of “limit” you had in mind. In light of the rest of your posting you may be thinking in terms of beam as a possible negative factor in ultimate stability. Viewed in that light, the critical factor is not beam in relation to length but beam in relation to draft. In this case the beam is quite moderate in relation to the draft and the “Sovereign” has a very wide range of positive stability. You state that in the event of being rolled upside down the flush deck would create “suction”. Unfortunately you have been misinformed there. I suspect that someone noticing that wide flat open boats with flotation low down in the hull were more stable upside down than right side up created the idea of “suction” as a possible explanation. However I assure you that the ordinary concepts of the relationships between center of buoyancy and center of gravity are perfectly sufficient to explain static stability questions. Also as a general case I think you can see that suction cannot exist where a solid object is floating in a fluid which is free to move in any direction. If you don’t see this right off, I can refer you to some standard naval architectural texts which to a reasonable job of explaining this, or I can construct some simple experiments that you can do at home to prove that shape and center of gravity determine the relationship between center of buoyancy and center of gravity and thus the stability of the vessel. Actually you gain a lot of righting moment when the mast is immersed. Remember that this is a solid wood spar. As soon as it touches the water it starts providing buoyancy and thus moves the center of buoyancy away from the center of gravity even further thus giving the vessel a substantial jump in stability. Our students who’ve done the stability tests for our YDS Lesson 6b can confirm that the gain is stability is quite dramatic. In fact this is significant enough that I feel very strongly that the masts of all offshore vessels if not solid wood should either be foam filled or sealed shut so that they provide flotation. I hope that this helps. Believe me these vessels are conservatively and scientifically designed to be ultimate offshore voyaging family yachts working not only from naval architectural principles and the experience of others but from our own experience as well.