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post #14 of Old 01-19-2010
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I want to touch on a couple pounts raised in the posts above. Olson34's post is somewhat outdated regarding boats that are balanced fore and aft and his comment about IOR boats going to weather.

In the late 1970's and into the 1980's designers began moving towards boats with finer entries and more powerful sterns. At first these boats tended to develop a tendancy to jack the stern out of the water and force the bow down causing the boat to develop increased weather helm, which forced the helmsman to use more helm which in turn meant greater drag and so poorer windward performance in a breeze. But by the late 1980's and into the 1990's designers learned to model the hull shape so that there was not a large shift in fore and aft trim with heel. They also determined that a fine bow helped with tracking and leeway, and that more powerful stern sections permitted greater stability without the inherent motion comfort and limit of positive stability liabilities of an over dependance on form stability.

When it came to rising up on one of their fat stern quarters and try to round up, there was nothing worse than the later IOR era boats. But also while it is true that the IOR boats generally make their best VMG pointing slightly closer to the wind than more modern designs, they tend to make a lot more leeway and do not have the upwind speed, and so the are not especially good up wind compared to a more modern design. And as a broad generality IOR boats do not handle a chop as well as modern designs.

Next worse and not all that close would be boats with moderate beam and a clean run aft in the hull form like all the descendants of the Cal 40, the Cascades, the Niagara's, and others. These boats have a lot of drag generated by their large amounts of wetted surface and their inefficient keels and rudders.

It is also a mistake to say, narrow fins with bulbs tend to generate more leeway than wider fin sections. At very slow speeds in moderate winds, as would occur immediately after a tack, a deep, narrow fin will make slightly more leeway than a larger surface are, lower aspect ratio fin, but the deep aspect ratio fin has way less drag and so accellerates more quickly, and almost immediately generates enormous lift as compared to older style keels. That said, these more efficient keels take a little more skill to sail well, since they do not tolerate pinching as much as older keel types. But while it takes a little more skill to sail with these modern high aspect ratio keels, they make way less leeway than earlier lower aspect ratio keels.

The other thing about a bulb is that it acts as an end plate, tricking the keel into acting like a higher aspect ratio than it is, delaying stalling and reducing drag due to the tip vortex albeit a partial trade off since a bulb adds small amounts of drag due to more wetted surface and frontal area.

I also disagee that most racing hulls are optimized for downwind sailing. These days there are still designs optimized for particular venues, but the majority of modern race boats are optimized for all around performance, meaning the have their performance optimized for all points of sail, but especially upwind and deep reaching. The fine bow, eliptical hull sections and moderately full stern sections that were popularized on IMS typeforms and carried over into the newer IRC boats, go upwind with a more comfortable motion, minimizing disturbance of the flows over thier sails, keel and rudder, pointing higher, making less leeway, and exceeding hull speed and with boatspeeds that sometimes exceed true wind speeds producing tremendous VMG's with smaller crews than earlier designs. And while ULDB's (ultra light displacement boats- typically L/D under 115) are still popular for Pacific downwind racing, but for the rest of the world, ULDB's are an outdated design concept that neither makes sense for cruising or racing since they are one trick ponies and modern racing requires boats that go upwind and can reach well.

Both the Compact 16 and the Westerly 25 are classic cases of boats with a lot of wetted surface and inefficient sails and underwater foils. That said, I have always liked the Compact 16 for messing about in shoal draft waters.


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