Originally Posted by samc99us
2) I'm not sure the sinking hull correction applies only to H14's and H16's. I would have to dig into that more. Will probably knows the answer off the top of his head.

Direct quote from the SCHRS calculator: "Sinking Hull (Only for HC14, HC16, Prindle 15 and 16".

4) I was quoting the Isotope class website, NOT the F16 class website when making that statement. I'm not arguing your point that 45 years of technology hasn't made a significant impact on boat speed, because it has, but the Isotope manufacturer is claiming the boat as a fantastic trainer for the Tornado (same statement made by the F16 class) and they are the ones claiming the boat performs as good or better than an F16!!!!

Please let's distinguish between marketing hyperbole and reality.

5) When looking at the SCHRS numbers, one big thing sticks out to me in general, and that is platform and sailing weight matter a healthy amount to the final number. I would weigh your actual platform if at all possible, as I suspect it is heavier than the 113 kg you have quoted (even the Blade F16's aren't really there). That could drive you back to a more 'fair' number.

Yes, SCHRS places a large performance factor on platform weight. Yes, the Isotope Class Rules specify a minimum weight that is unrealistic. 275lbs would be a more reasonable number, and I understand that most Isotopes weigh at least 280. Rather than trying to get a rating for MY PARTICULAR ISOTOPE, I was trying to get a rating for the class, and SCHRS uses the Class Rules for that. I can contact the manufacturer to try to fix the class rules. A 1.1% change in minimum boat weight yields a 2% change in rating. In racing against other sailors who weigh 25 pounds less than I do, I don't see that large a speed difference on the water.

6) SCHRS may not be creating a perfect number for your boat in a long downwind race, but take a look at the Taipan 4.9 numbers. I'm referencing that as I believe it is pretty similar to the Isotope in many ways (including design age).
According to sailboatdata.com, the Tiapan 4.9 was designed in 1982. The Isotope was designed I'm 1962 - hardly the same design age. Please note that the Tiapan 4.9 was also billed as an F16 class boat but it does not carry the F16 rating. The Taipan 4.9 Solo has an SCHRS rating of 1.097. I'd be quite happy with that rating for an Isotope.

The big thing is they race without the jib in solo mode. Add the jib in and you drive the number from 1.097 to almost half, or 0.980. That may need some looking into on the SCHRS side as I doubt the boat is actually twice as fast with a jib as without.

That's a point I've made before which has fallen on deaf ears. If I were to take a 40sqft jib off the Isotope altogether, and add a 188sqft spinnaker (the standard F16 size), then the Isotope SCRHS rating would go from 1.050 to 1.108. That's right - add 148sqft of sail area (a 58% increase) and the boat gets 5.5% SLOWER!

Looking at things a different way, if you sail an F16 class boat single-handed with main and jib, rather than main and spinnaker, SCHRS says it will be more than 5% faster. According to SCHRS, jib area is 9 times more important than spinnaker area. That makes no sense whatsoever. If it were true, then nobody would use a spinnaker at all!