I think the spinnaker luff on the Nacra F18 is a bit longer than that of the Tiger. By about 6 inches. The jib should work okay provided both are from self tacking boats setups. The luff of the mains are withing about 1/2 inch of each other, but you would need to change out the headboard.

You can do this if you are not interested in the fastest boat. The masts are very far apart in terms of stiffness. If you are getting all the sails for free and using them for pleasure sailing only I would say okay. If you are a racer I would say nay.

Jay and Pease Glaser can make you a sail based on your weight and mast bend. The problem may be determining how to relay the mast stiffness to them. Glaser Sails

Later,
Dan