"A while back I talked to a sailmaker about this, and he said the term gennaker can be ambiguous, so if somebody orders a gennaker, he has to have them clarify exactly what type of sail they are talking about. I think the term "spinnaker" is universally understood, which is why I suggested using that word in the rules. Not everybody is going to go down and check the definitions if they think they already know what a word means. It would be unfortunate if somebody ordered the wrong type of sail for this class just because of a simple word misunderstanding. "

Mary, it would be impossible to make a sail that doesn`t conform to the class rules, as long as you actually READ them first !
The rules on a spinnaker / gennaker / hooter are so simple it would be incredibly difficult for a sailmaker to get it wrong such that your sail doesn`t measure. Whether you call it a gennaker, spinnaker, hooter, screacher, reacher, code 0, or an inverted apex g-string bikini really doesn`t make a difference.(My apology to all skydivers or parachutists, and ladies who floss behind).

What matters is that your max. hoist height is 7,5m, your max. calculated sail area is 17,5sqm, and your mid-girth measurement is 75% of the foot length. (Unfortunately the measurements are metric, and the method of calculating sail area is done according to ISAF calculations, so I can see a lot of resistance from American sailors to want to belong to a class that works according to International methods, and doesn`t do things the American way.) There`s also a rule on pole length, which will determine the max. aspect ratio to a certain degree. The fullness/flatness, position of max. draft, luff, leech & foot lengths and a host of other design variables (most of which I`m too stupid to understand, and that`s why I`m no sailmaker), are just that - variable. A sailmaker who knows how to make catamaran sails and claims he can`t be creative within the class rules has no clue on what he`s doing. But I`m going to assume your sailmaker won`t get it wrong.

I think the term Gennaker came about when, on keelboats, cruising people started putting spinnaker type sails on their boats without a spinnaker pole, and you gybed it as you would a normal jib ie you turn it inside-out, and it was assymetric, meaning it`s leech & luff lengths were unequal. It made things a lot easier and hence hit the cruising market first. It was called a "gennaker" by sailmakers first, so I`m dumb-founded as to why THEY would be the ones who think it`s an ambiguous term.

I think you can sum it up as follows:
Spinnaker : symmetrical foresail, gybed such that the leech on one gybe becomes the luff on the next gybe, and is set on a gybing pole. Has a port & starboard clew, rather than a tack and clew.
Gennaker : assymetrical foresail, is turned inside-out when gybing, and has a tack and a clew. (meaning the tack is always fixed at the pole end while set.)
If I`m half-way right on these definitions, what we sail with is called a gennaker, unless you gybe your pole as you would on keelboats. I think the term spinnaker has crept in and got used by sailors, not sailmakers, and it`s what we got stuck with, even though it might not be correct terminology. Who really cares ?
Steve