IRC Rating LL/P - Performance Cruisers - The IRC Rating LL/P debate

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IRC Rating LL/P
Performance Cruisers - The IRC Rating LL/P debate.
Following on from my study of Performance Cruisers vs. various rating systems (including IRC), and the sometimes huge variances between similar yachts and on the water performances as well as to IMS type VMG models. Most single number regression formula?s use a combined sail area in model (with various weightings such as main at 100% and foresail at 60% to allow for upwind tacking, and 40% for downwind with spinnaker). But, these regression models have one or more extra tweaks to allow for genoa overlap advantage and offwind angles too close for spinnaker to be factored into general regression #.

This is usually the above measure (times by) of LL/P or FL/P in the equation. With a masthead rig, and P always being a substantially lower measure than LL or FL, and with a net LL/P relationship of about 1.1, this ratio will always increase the regression formula rating of masthead yachts. In the case of fractional rigged yachts, the normal template (current IRC optimized) would be about LL/P of close to 1:1, so very little to no adjustment in this case. But some of earlier fractionally rigged yachts from the mid 80?s to early 90?s have below parity relationships (0.90 to 0.95)with big P measure?s relative to LL measure and sometimes show a very nice IRC Rating in spite of a mix of other not so advantaged features such as poor spinnaker bias etc. This feature was very common to said Lavranos, Simonis, smaller J-Boat designs and classic?s (such as Swede 55 style) over this period.

When we get the post 2000 Performance Cruiser fractionally rigged cruisers, with looks of IRC racers (but with very high boom to prevent cruiser?s crew getting decked) and with short measures of mast above hounds, we end up with masthead style measures of LL/P or FL/P of about 1.05 to 1.1. The regression model would then ?read? this LL/P measure as a high overlap style and give it same costing as a conventional masthead rig. The only difference here is that a masthead rig would have a genoa /mainsail relationship of about 60:40 (with big drive in slot), while the Performance Cruiser would be about 50:50, the same as normal IRC fractional yachts?.. At the displacement end of the fleet, said rating # anomaly?s become very obvious.

Obviously a LL/P factor of 10% above or below median point is a high number, but all sail area ?power? models work on numbers in equation of somewhere in region of square to cube root of sail area in said regression equation. In the real world of rating #?s, a masthead rig with normal 60:40 genoa /mainsail bias would rate about 2.5 to 3.3% higher than a fractional rig.

Perhaps members of rating forum(s) will see the IRC Ratings of Performance Cruisers in a new light?

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