Jeff

Typically a catamaran rig has no backstay because of the high roach sails used. The mast is held from going forward by swept back side stays. The mast itself is kept from breaking while flying a large spin by maintaining main sheet tension (in effect a backstay of sorts) This feature works very well in catamarans beacause they are able to generate significant apparent wind, and hence keep a large amount of mainsheet tension with correct sail shape while going down wind.

You may want to explore whether you can accomplish this with the semi-planing hull of your boat, or rig some kind of doubler back stay while running the spin. Busted spars are ususally no fun and very expensive.

Good luck

Matt