The dolphin stricker creates a counterforce to the mast pushing down on the beam. Without it your beam will collapse the first time you sheet in hard. It should definitely have some tension without the mast on.

There is a procedure by Nacra to set the dolphin stricker tension. I had it on a piece of paper somewhere for my 5.2, but it probably was in the file I gave the buyer when I sold it. The tension was set to induce a curve on the round mainbeam. But the inter series have a different beam, that are not just circular, so the procedure might be different.

I'd suggest you give a call to your nearest Nacra dealer.