What do you guys think about fixing, with rivets, a swivel cam block on an Inter 20 carbon mast to raise the spi? Is, in your opinion, the structure of the mast strong enough to sustain the stress of the sail?
Thanks in advance.

Yes - but secure it with high modules lines like used on modern F18s. In fact, you only need to remove the bail and drill a couple of small holes in the side of the luff track.

Here is something close...Instead of tying the line all the way to the head of the mast, use the small eye strap that is already riveted there for the spinnaker halyard hoist tail. Actually...that's all wrong. Don't run the halyard up the mast either, just run it to the block and use the line at eye strap to hold the block in place...hang on, let me see if I can find a better example.

Actually, do it sort of like in This Thread

you just don't need the double line going to the top of the mast...just a single going to the existing eye strap.

I think he might be asking about using a swivel cam cleat on the mast (new school) vs. the beam mounted cleat (old school N20) that holds the spin halyard.

Aaaa...well...carry on then. I think all of ours were on the beam and not the mast. Heck...I had a hard enough time keeping the F18 one on the mast ON the mast...ripped off three times until I pulled everything apart and mounted a backing plate behind it.

I had to have two beefy cam cleats on my beam for the halyard on my N20 to keep the halyard from slipping when team beef got on the wire during a spin reach.

We're going to end up doing that on the F18. I thought we had it solved but we lost the spinnaker halyard through the cleat three times in the FL300. I've tried three different types and style of line and although one worked better, it burned holes in the kite badly and was a poor trade off.

We also had to put core back in the stripped cover... that ended up solving the issue long-term.

But the halyard with the core and a single cam didn't work.

I solved the issue on the F20c. If it would hold for that beast on a reach, nothing could make it slip. There's a pic somewhere on the forum.
I cut a piece of 1/8" G-10 and mounted it to the ears of the swivel cleat. It had enough room to put H150 cleat and a micro cleat as a back up.

Found it

I riveted a swivel cam cleat on the I20 mast, no problems.

I have a short section of "second" cover over my halyard around the area the cam cleat grabs when hoisted. So that area is fatter due to core + cover + second cover. The cover(s) are whipped to minimize slipping.