The Hobie-18 is originally set up with loose diamond wires, not a pre-bend rig. The tuning guide specifies "tightness" by pressing the wires together to the mast. "Tight" meant they touch the mast about 6 inches to a foot above the lower mount, "looser" to various degrees meaning the wires touch a foot or so or more. This means the mast bends along the minor axis of the mast section, and the windward diamond wire will be loose.

Alternatively, many Hobie-18 sailors (me included) tighten the diamonds to the point that the mast doesn't bend side to side, but not enough to induce prebend. Then the downhaul produces mast bend on the major axis of the mast section (front to rear). I also set my spreaders for very little to no rake.

For the shrouds - in light air, a tight rig will inhibit mast rotation. Again, the original tuning guide has varying degrees of tightness to the shrouds, being tight only for big conditions. I tended to run mine a bit loose unless the wind was up.

If the mast has a bend to it - you might try to straighten it. There have been lots of posts on this board about this - try a search.