If you have lee helm with the spinnaker up on a Tiger, you had better rake your mast back more or check your rudders. That will happen when you add a big spin. to a non-spin design, like my old Nacra 5.5Sl. But the new boats (F18's, I 20's) that were designed with spins are very well ballanced with the spin up, usually have a very neutral helm going down wind.

The trick is to go downwind on one hull as long as possible, when it starts to come down, head up, fly the hull and continue to bear off as the speed builds. This is when most spin boats stuff so be careful if you are practicing in big wind. The very act of bearing off with a full spin will push the lee bow down, until you get some speed up and get it stabilized. You have the full weight of the boat, both crew and the full sail plan (spin included) pressing down on that lee bow, which is pretty skinny on most F18's.

That's why I love the Inter 20, with those big, fat, long bows, when you double trap downwind, you really have to try to stuff it. Still it's almost impossible unless it's really blowing. You just don't see too many I20's pitchpolling. You will see some F18's stuff, do you have footstraps back there to keep you at the back of the boat when it happens? Get some if you don't, and get some beach wheels before you destroy the bottoms!