Very unusual to need to limit rotation when boomless. the back edge of the mast needs to point at the shroud upwind, but sheeting in the sail combined with the jib slot pressure forces it more fore/aft. the only reason darts have the line is to rotate the mast on a gybe
I'm not sure why I need to, but on an upwind leg the boom certainly seems to be rotated too much, it has a very sharp angle to the sail. Looks to be over 45deg to the hulls, and forward of the shrouds. That is with a lot of main sheet tension. If I force the mast to be more straight by pulling on the diamond wires I can get the tell tails to flow on the inside of the main sail and the angle seems to line up better with the rest of the sail shape.
In light wind it's right with the sail "baggy", but in heavier wind 15kt plus I feel I need a flatter sail and less rotated, pulling on the downhaul flattens the sail but the rotation is now too much now in relation to the flatter sail curve.
Maybe I got it wrong but it certainly appears to be over rotated in heavier wind with a flatter sail.
