Quote
I totally agree, however, that often statements of hull length are assumptions without data. It is quite common to think of hull length in association with sailing in displacement mode, i.e. longer hulls = faster speed. For a 20 foot non-planing keelboat (monohull) the theoretical max speed is ca 6 knots. Beach cats easily sail much faster than that, hence it is obvious that we are often not in a pure displacement mode. We do not need the long hulls to have fun.


For the most part, cats are displacement vessels. The difference in the correlations between length of hull and theoretical max displacement hull speed is due to the fineness ratio of the hulls (length/width). The correlations that hold mostly true for mono's don't for cats because of this. How many boats outside of cats do you know that have lenghts of 20' but are only 1 1/2 feet wide?

I don't know if the additional length truly makes for a faster hull. Theoretically, it should b/c the same principals regarding length still apply, however survivability of a 20' hull feels much greater than an 18' hull. Even with more power, the I20 feels much more comfortable than the F18 in a big breeze to me.

I've sailed two different light cats (18HT and CFR20) in big breeze and felt the 20' boat even with a bigger sail plan was more controllable. It seems that as the boats get lengthened the majority of the length is out front and that helps keep the pointy end up.