That formula comes right out of the US Sailing Race Management Manual. It applies to all boats, not just catamarans.

The problem with a line that long is people tend to bunch up at the ends - especially if you're using an "I" flag as the prep. People in the middle of the line that are OCS are "more" penalized by having to sail to one of the ends in order to start properly - as opposed to someone at the end who could just spin around the pin. That's why more and more PROs are using the "Z" flag (20% penalty)instead. It penalizes everyone who is OCS equally - and the penalty sticks, even if there's a general recall, making you think real hard about being aggressive on the re-start.