I've done the beam and dolphinstriker calc on for example my boat (Formula 16) and the Blade F16's.

If you give me the exact specs on your boat and beam I can tell you what the stresses and deflections are and tell you wether you need a dolphin striker or not.

But from the data give as of yet. 4 inch diameter beam (100 mm) and 4.5 ft bridges space and the describtion of the old wooden trampoline I would be very surprised if you need a dolphin striker for this boat.

Of course it all (now) dependents on the wall thickness of the beam and the sail area on the boat. But it is very diffucilt to get beams of this diameter with a thinner wall than 1/10 inch (2.5 mm) and it will probably by some 1/7 inch or thicker (3 mm or thicker). So the original builder probably used heavy beams. I would expect to find that they hold up just fine without a dolphinstriker. But of course I will not say anything definate due to US legal practices.

Give me the wall thickness of the beam, the mainsail area, jib area, mast height and distance between sidestays as well as distance rear beam to front beam and front beam to bridle points. The last measuered parallel to the hulls. You don't have trapezes I see is that right ?

There is also a easy trick to see wether you MAY need a dolphin striker. Rig the boat on land sit rotate the boat a little away front the wind sit on the hull and pull the mainsheet really tight Without flying a hull. If the beam flexes significantly than you'll need a dolphin striker. Most boats flex by some 5 mm to 10 mm in the middle of the beam (2/5 inch). Dolphin striker less beams can flex a just little more but handle the loads just fine.

Wouter