I have an older Nacra 5.7. Like most 80s nacras, it has two round cross beams attached to the hull with a bolt and flange inside the crossbar and 4 bolts holding 2 straps at each hull/crossbar connection.

I have broken off the bolt in the crossbar AND one of the bolts that hold the straps. Efforts to remove have failed. On the strap bolt, I was able to drill out, fill with thickened epoxy and plan to re-drill and tap with a helicoil. On the center bolt, whatever held it in place broke away. It appears to be a flat metal threaded piece.

Does the bolt in the cross bar do anything other than hold the hulls from slipping down the cross bar? Since this is the only side where I can remove the trampoline, I don't want to epoxy in studs unless it's the only option.

I want to avoid a sawzall if possible. Any suggestions??

The bolt in the cross bar keeps the bar from rotating and moving as you suspected. The other bolt should keep that from happening. the fitting the bolt slides into is called a moon washer.

I did a similar thing last summer on my 91 5.8. I stripped the inner and simply epoxied it in place. I also stripped and had to retap(one size up) one of the strap bolts. My dealer told me to never ever toque these down as all they are tapped into is a thin aluminum plate. Be very careful! You only need to hand tighten. They are designed to shear away before the hull gets damaged if the boat is subjected to violent twisting. Your idea will work.

I called the factory when I removed the center bar on my nacra 5.2 which connected the rear and front crossbars, which was there to prevent the front crossbar from twisting. They suggested that I put SS or monel rivets through the beam straps into the crossbar, they said to place them at 10 O'clock and 2 O'clock. This should prevent the crossbar from moving. It worked.

Oops forgot to mention that the previous owner riveted the bar to the hull straps as well. good suggestion.