How does the TALL RIG on a 4 FRICKIN FOOT wider boat make up for 1 foot of length? The spi is rated on the 21 butt not on the 20.
ARC21 mast is 33"
Is waterline the defining factor?
Inquiring minds wants to know?
Easy, go onto the SCHRS site and pick up the free ratings calculator, dial in your weights beam etc and bingo you have your rating.
Oddly enough beam has very little input, however if you put beam and sail area up goes the rating exponentially.
Interesting to put a few of the manufacturers boats in with true figures ( like including mast area which one major doesn't ) and see where the ratings go, no wonder you get beaten sometimes on handicap.