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I think the original question on the other site dealt with tracking in waves. My current understanding on this issue is that tracking in waves is more an issue of the bow and less about the stern. A boat with a full bow and deep bow sections will tend to root, by which I mean that the bow digs in, built resistance and tries to slow the boat relative to the forces trying to puch the boat forward. Conceptually if the bow is full, it adds has little or nothing to directional stability allowing the ends to begin to veer off to one side. This is the reason that is generally cited for displacement powerboats broaching in following seas and why tradtional cruising boats generally do not do well going dead down wind in big seas without towing a drougue as a way of keeping the loads on the bow to a minimum.
If you take a full stern and couple it with a full bow, as Catalina tends to do, then you have the worst of all worlds, because the full stern is exerting even more force on the bow causing the boat to want to swap ends, (think of it as an arrow flying backwards).
But when you look at the better IMS/IRC style designs, the forward end is quite fine and sterns are not all that broad, and great care has been taken to avoid longitudinal trim changes. As a result they do quite well in a following sea, certainly better than the more traditional boats that I have owned.
As to the quote from Principles of Yacht Design, Lars Larsson and Rolf Eliasson, third edition"
"This may be good for the surfing abilities of the hull, but it is not good for the course stability when rolling. When the hull heels over, the centre of buoyancy moves much more sidewards in the stern than in the bow. The force required to move the volume of water sidewards comes from the hull, which by law of action and reaction is affected by the same force from the water, but in the opposite direction. The stern is thus affected much more than the bow, and the hull changes its course in the heeling direction."
I think this is a little bit dated. It is my understanding of the current design concept of fine bow design runs counter to the thinking that is being described above. My understanding of the current thinking is that it is not the fact that the center of buoyancy shifts outward on the hull that causes roll steering but the potential for assymetry of the underwater hull form. In older or poorer wide sterned boats, there was little regard for the heeled shape of the hull, and in many cases the heeled hullform produced a form that looked like a boat with its rudder hard over. That was also the case with many more traditional, narrower designs as well because of the wide proportion of waterline beam to waterline length. The better designs of today are carefully modeled so that their heeled hullform promotes tracking rather then turning, and careful roll and pitch dampening reduces excitation rolling and thereby roll steer.
Respectfully,
Jeff
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