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Old 04-16-2013
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IMS, ORCI, Open boats and sailboat design.

Quote:
Originally Posted by bjung View Post
I thought this article ( even if it is 5 years old ) fits well into some of the discussions here on boat speed regarding sail aerodynamics, angle of heel and the influence of beam. http://www.sailyachtresearch.org/ima...e_july2007.pdf
Yes and also why the last generation of performance cruisers are better sailing boats than the previous generations. I am talking about boats with a keel all in lead without a bulb versus bulbed boats, boats with more RM, more powerful and faster. Those powerful and stiff boats rated badly some years ago so the boats that won races (in compensated) were not the fastest or more seaworthy ones and that lead the design of cruising boats in that direction.

That has changed and since some years ago the results in real time are much more equivalent to the results in compensated time. The only exception were very light boats with a big B/D ratio of moderated beam, that were in fact much faster but had problems in winning in compensated.

I have been posting here news about the meetings the racing community has promoted with designers and the ones that makes the rules to address that problem. Some alterations on the good sense have been made in the last couple of years to resolve that on ORCI and today that handicap rule seems to have reunited a consensus in what regards a future rule for all. Some resistance from the ones that have boats that rate unfairly better in IRC is expected. Much work has to be done but all seems to go in the right direction.

That story about boats with a smaller stability and not as fast as they could be is funny because many still think that twenty or fifteen years old cruiser racers are better as cruising boats then the most recent crop of cruiser racers when it is the opposite: Old boats tend to be tender were not designed with performance in mind but to suit a rule that favored slow boats and boats with a smaller stability:

"Despite this narrowing of designs in the ACC box rule, the opposite trend became evident several years ago when trying to handicap using a VPP. For IMS this meant optimal designs started exhibiting less and less stability, with bulbs disappearing from the bottoms of keels to be replaced by fin
keels. The tips of fin keels were soon composed of materials other than lead as high-performance deep-draft keels were regarded as desirable but so was low stability. ...

In any case, designers concluded that the VPP overvalued stability. A tender
boat was predicted as slower than it actually was, so the obvious solution for
designers was to exploit that bias: make the boat slower knowing it would not be as slow as the rule predicted. With that rating credit in hand the designer could then make a longer, bigger boat, perhaps with more sail area, to get the rating back up to that of the competitors. The end result was a boat that although tender was actually faster through sheer size.

Without rule considerations, however,these boats were not as fast as they could and should have been for their size.

Although the Offshore Racing Congress have recently taken steps to correct the problem in the IMS VPP, it was too late and the favourable treatment of undesirable designs partly contributed to the demise of IMS racing here in the US...."


http://www.sailyachtresearch.org/ima...e_july2007.pdf

Tn Europe the result was a kind of separation between racing boats and cruiser racer boasts. While the first were designed to perform as well as their size allowed, the others were designed to beat a given set of rules and that unfortunately means not to be developed taking performance in mind but winning on handicap, not real time.

The ones that liked fast boats quickly started racing in several one design series or Open boats with a very open rule. That lead to two divergent lines of development (I would say three of we count solo racers) in what regards boat design, something that had never happened in the past.

Logically the one that shows more influence on cruising boats today are the one that comes for solo boats, boats those were designed with performance in mind, out of almost any rule but because they were designed to be sailed in auto pilot most of the time they had to be easy and forgiving boats to sail, a condition that suits perfectly cruising boats.

Most performance cruisers, because they can be used as cruiser racers come from the line of the IMS boats (Handicap racing) but now corrected in what regards stability and speed and others come from the development line of solo racers. Curiously they are fast boats but has not any use for racing: They were designed taking only into account pure performance and easiness, not any handicap rule and therefore rate horribly bad. Anyway there are many sailors that just don't care: They don't want the boat for racing, they want just a fast easily driven cruising boat. That is what explains the success of boats like the Pogo or the RM as performance cruisers.

Regards

Paulo
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Last edited by PCP; 04-16-2013 at 01:38 PM.
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