One thing to keep in mind when you ask the question which is fastest is that, especially with boats like skiffs or Moths, you have to actually be able to keep the thing upright. My guess is that even the top level moth sailors capsize a lot more frequently than top level cat sailors. If you're on your side, you're not going fast.

I suspect that in most cases around a course a beach cat will beat a skiff or a moth. The long narrow hulls make a cat's average speed very good. The San Fransisco Bridge to Bridge race allows cats, skiffs, windsurfers, and kiters. I think the windsurfers and kiters usually wind that one, but I'm pretty sure it's set up to be a downwinder.

Having spent a little time on an International 14, I will say that double trapped planing off the back of one of those boats in 15 to 20mph is a very unique experience compared to cat sailing and if you have the opportunity, it's worth the ride. And I would personally jump on the opportunity to try a Moth regardless of what it's top speed actually is.

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