A quick measurement on the picture suggest a girth much closer to 50%

I seem to recall that the Tornado class rules actually do not contain a 75% girth rule as the other classes know it.

Someone has to check this but I remember the Tornado class only setting max lengths on the foot leech and luff of the spinnaker sail and limit area and shape that way.

Actually the hooter is a rather old racing sail. The ORMA tris used to have one as far back as in the 80's/early 90's. It is just that cats class rules disallowed such sails by rulings like the girth rule.

Wouter