Thanks for your comments Alan. I can understand why a heeled sharpie will cut the water better and pound less, but I'm less clear about why having "good way on" will smooth the ride. It seems to me that the faster you go the further a bow can extend out of a wave, the harder you hit on the backside of the next wave.
I'm still working on the 'gentleman' aspect, so want to keep my windward options open.
I sort of intuitively understand your 'dD/dVv' idea, but wondered if it was an actual formula that boat designers use? If so, how would you do the calculations, and what would 'good' and 'bad' numbers look like?
Can you give any guidance on how to match stern lines to bow sections?
The dD/dV (derivative of displacement over derivative of velocity) is the only way I could describe the function, though I am sure there must be an equivalent nautical term. Usually I help design airplanes.
Balancing the forward buoyancy of a vessel with the aft buoyancy is explained quite well in Brewer's book, but traditionally one wants a wave lifting from astern to NOT bury the bow, and the bow climbing the back of a wave in front to NOT sink the stern. This assumption, or concept, led to a steady rash of double ended cruising boats, though Perry and many others have shown that one can design a boat with similar rates of increase in buoyancy above the WL fore and aft, but completely different external shapes.
A boat with some inertia, i.e. displacement (mass) and/or speed, will lift up over a wave form as it catches up IF the bows rate of change of buoyancy is enough. If not, it will bury in the wave back. Hence the good speed comment. Good inertia, and a flared, or raked, bow will lift the bow UP, rather than stop the boat. Good inertia, and a narrow, fine, bow, will usually bury the bow, and stop the boat dead.
I notice that modern light displacement boats, especially those with fine, vertical, stems, and wide buoyant sterns, can easily be driven into the back of a preceding wave, whereupon the boat nearly stops, and possibly broaches. Clearly acceptable for racing, I sail like is a lot, but not so for cruising, where the crew is short handed, and the boat needs to take care of itself without constant human input.
Hogfish, AS 29/39 et-al are all designed to have a near vertical stem with a fairly fine entry forward, and near vertical forward sides. Ie the buoyancy forward rises nearly linearly with vertical movement. This is fine, as long as it is paired with a similarly fine aft sections, where the aft buoyancy also rises near linearly with vertical movement. This should give a smooth comfortable ride, even in weather, a fact confirmed by 'Hogfish' et-al. The fact these boats also have relatively low total weight (mass, displacement) on relatively high buoyancy, makes it still harder to drive their bow under the back of a wave, and a following wave will tend to push them (surf), rather than push them under, or bury the stern.
I like it.
My own larger, newer, boat designs, have vertical stems with little flair, moderately flared mid sections, and a wide flared stern. Not only do these usually need twin rudders just to keep one in the water at all times, but they are a real handful to sail. They are designed to sail to windward heeled at 15', and reach and run basically flat. I always have the forefoot immersed a few inches at rest too. Griffith's once placed a chine right on the waterline where the owners head rested when he slept aboard, and the the owner never let Maurice forget how hard it was to sleep at anchor with a faint ripple on the water. I have a similar horror where the bow is concerned, wavelets slapping under the bow at anchor.
I also like to calculate the shape of the heeled hull, in later cases rotated about the center of buoyancy skewed to port or starboard, depending on heel. If designed correctly, this plan shape will be a foil lifting powerfully to windward. See CAD image.
In this case, the boat is most efficient heeled at 15' bow down (stern free of the water) sailing to windward, and flat, 0', stern immersed sailing downwind.
Currently I am involved in designing and building a sailing dinghy for the Hardware Boat Challenge.
http://www.boatdesign.net/forums/sa...input-proposed-rules-42343-55.html#post736278
But I am already thinking about the next boat. I am tempted to build something like a scaled up Bolger EEK, possibly with water ballast. I wonder if any such have been built, and if the hull actually works.