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From: Tom MacNaughton
Date: 29 Dec 2007
Time: 07:35:00 -0500
Remote Name: 66.252.37.86
It pains me to disagree with Howard Chapelle on anything and as far as traditional design and boat construction go about there are only a few things I disagree with him heavily on. One is his method of deducting planking thickness. However this theory that buttock lines are good predictors of speed or seaworthiness is really pretty far off. For those of you with the revised edition this section is on pages 168 and 169. Unfortunately he had a bit of a blind spot on water flow and didn’t seem to be able to visualize it very well. The only boat on which buttocks would give any reasonable idea of water flow would be a flat bottom boat where the water flow normal to the surface would be equivalent to the buttock lines in the area of the flat bottom. Perhaps it is not coincidental that Chapelle had a great interest in flat bottom boats. In actual fact water flow generally follows lines that might be visualized as being the intersection between the hull surface in the area examined and a plane normal to it. That is a longitudinal plane which cuts the surface at a 90 degree angle to it. As it happens there is a family of hull lines which can represent these waterflow lines quite well. These lines are diagonals. In hulls with a lot of difference in general shape of sections from one end to the other you may need as many as three sets of diagonals to evaluate the forebody, midbody, and aftbody respectively, but they are enormously helpful in getting the best performance out of all types from heavy displacement sail and power vessels all the way to very light high speed planing powerboats. To give you examples of designers who paid or pay special attention to the diagonals we can cite Nathaniel Herreshoff, Colin Archer, Olin Stephens, Knud Reimers, K. Aage Nielsen, and J. Laurent Giles. I’m sure that there are others who have placed a similar emphasis on diagonals, but have kept it pretty secret. Herreshoff, Stephens, and Giles at least normally did not publish any lines showing diagonals during their working lives as I believe they considered the diagonals a secret of their success. I’m sure you will all recognize that in their respective countries and even internationally these designers would all be likely to be found on people’s lists of “greatest designers of all time”. Very early on in our career we adopted and gradually refined the process of creating lines using heavy emphasis on diagonals and we have felt that following in the footsteps of these great designers in this manner largely accounts for our rather extraordinary good luck with the performance of our own designs. Now, to go back to vessels based on the work of Colin Archer. We have prints taken from the lines of the original Colin Archer sailing rescue craft or “redningsskoites”. Here the diagonals are numerous, clearly shown and of very good character. These days we would recognize that they are slightly too full in the ends given what we know now but they are still so good that there is little point in altering these lines after over 100 years. Anyone who knows the history of these vessels will know that they are extremely seaworthy. The original redningsskoites operated only in the winter in the far North Atlantic off the coast of Norway, which is a lee shore. They would have to sail into cul-de-sac harbors, often sailing in backwards, in full gale conditions and then sail out again towing vessels behind them. Their seaworthiness is legendary and beyond question. To understand everything that went into making them so seaworthy you should read “Seaworthiness – The Forgotten Factor” by C.A. Marchaj. As to the claim that these vessels were slow. This arises out of an extraordinarily persistent misunderstanding. The original Colin Archer sailing rescue craft sailed only in winter and virtually always in storm conditions. When some of them were bought out of service by yachtsmen and taken to sea, these people naturally were sailing in winds more like 12 knots than 65 knots. Yet it seems never to occur to people that for summer sailing and voyaging they would need more sail area. This extends to the “Eric” which is a modification of the Colin Archer by William Atkin, and to the “Westsail 32” which is an adaptation to fiberglass of the “Eric”. Both of these boats need much more sail area and can easily carry it if given about 38 to 40% total ballast. Give them an appropriate sail area for the conditions in which they are sailing and they will be extremely fast in both light and heavy airs. An example of how different one of these vessels looks when properly rigged is our own “Sagittarius 60”. Except for a very tiny refinement of the sheer that was possible because we know more about proper methods of sheer development these days, thanks to Cyrus Hamlin and a friend of his named Ted Earl at Mount Desert Yacht Yard who developed planar sheer principles, the lines are identical in shape to a Colin Archer redningsskoite. Needless to say buttock lines are very rounded on these vessels. However since they have nothing to do with the direction of water flow on this type it makes no difference.