I need some help on determining a fair Portsmouth rating for my Supercat 15 sloop.

It is my understanding that the 15 Uni is a 1-up boat, but the US Sailing table doesn't specify the Sloop being 1- or 2-up. I'm assuming 1-up.

Since the Supercat 15 Sloop (SC152) rating is (77.0) I know it is a dead class, but there is also no Beaufort rating provided and I don't know how to calculate it (if it is a calculation).

The Nacra 450 Turbo is practially the same weight, length, beam and sail area and is rated:
Nacra 450 Turbo 1-up N450T 76.9 80.5 79.6 77.0 74.4

SuperCat 15 Sloop SC152 (77.0)
SuperCat 15 Uni SC15 78.0 83.5 79.5 77.5 73.2

It wouldn't bother me if I just used the 450 numbers. It would hurt my rating, but that (to me) is better than artificially helping my rating and therfore cheating.

Also, I have a self-tacking jib which is slightly smaller than the original jib. I can't find a rule that would effect that change, too.

Any thoughts?? (besides buying a non dead class one-design boat??)

Ask Bill Roberts. He designed the boat and masters the Portsmouth yardstick. If he doesn´t know the answers, nobody does.
FWIW, the SC15 is a great family boat and, like the SC17, remains an active class over here. They have their nationals and a reasonable turnover in races.

The tables are fairly clear if you read the class weight table.

First of all, a boat sailed sloop must use the sloop number, not some sea-lawyer trick of uni plus jib. So call it sloop and start with the 77.0 number. The class weight tables offers both Super Cat 15 "Single " or "Double". Whatever that means is irrelevant since the footnote says, "SuperCat class rules state that in open class racing the number of persons on board may be increased or decreased." That means if you sail solo and you weigh more than 150 your good at 77.0. If you sail with crew and weigh at least 260 your good at 77.0.

Our fleet has a well-sailed SC15 sailed solo sloop and he uses the 77.0 base number and he kicks a$$ with a custom Bobby Johnson squaretop (requires an MN mod of 0.995 giving 76.6). Go Tommy!

Ah... the Florida Dart example... Was that debate ever resolved by the PN committee or did mob rule decide the rating?

Texel has the Dart 18 uni at 121 and the Supercat 15 uni at 120. Add jibs to both and he should be a little faster then a dart 18 sloop single handed.... No wonder the florida SC15 kills at that 77.0 rating! The single handed Prindle 15 main only has a 76.2 rating...

You want to add a jib and have a slower rating then a P15?

The () mean that less then 15 data points exist for the class and not enough data exist to give seperate wind adjusted ratings. So, I would say that his rating would be be sloop and take the L4 correction... or the single handed rating and add the jib correction.. (Assuming that the old data were for two person teams on the SC 15 main and jib).

I would probably go with the single handed rating and add the jib correction since he is using a smaller self tacking jib then the sloop rating assumes. so about 76.0 dpn