On the Nacra F18 the spi ratchet blocks are fixed on the outer side of the hulls, near the shroud adjusters. It is the factory setup.

Sometimes, mainly in small and medium wind I have a feeling it would be better to fix it on the inside part of the hulls, it would result a better spi shape. (performance spi, 2006). Also If I see the other models as Infusion, Capricorn, or even the Tiger or the Cirrus, all, mounted inside. I think these models also using the same cut spi.

Any suggestion ?

rig up a 'twinger' line with a small block that allows you to pull your sheet inboard to test. In my opinion, the cut of the spinnaker has a lot to do with how far inboard you can put your blocks.

Thanks Jake,
God idea for testing, I will try it.

If based on this tests I decide it is better somewhere inboard, what is your recommendation, as a "mount point" ?

I think I have 3 options:

1. The upper/inner corner of the hulls,
//could be a fix, stable sulution - but maybe I'm crazy if I drill the hull//

2. The side of the trampolin,
//simple to fix, but I'm afraid to break the tampoline//

3. Leave the ratchet blocks on the original place...

?

There is a reinforcement block inside the hull for the current blocks and you will need to do something inside the hull if you move them. Inspection ports just behind the daggerboard well will give you "arms reach" access to that area. However, be careful and check for bulkhead position...there should be one about 10inches behind the daggerboard well. You might be able to put the ports in front of the daggerboards but they might tend to be in the crews way or damaged as the crew scurries over them in and out of the wire.

On my infusion, I pop-riveted a pad eye to the GRP in the area of the tramp lacing points expecting to find an aliminium back plate. The spinny block has held up fine without any back plate. Testimony to the infusion process i guess but it should be ok on the F18 too.
A dab of epoxy in the hole before you squeeze up the rivet won't go amiss either.

That riveting sounds great. Were you using aluminium or steel rivets ?

On your infusion was not it the factory setup ?

Thanks !