>>As Wouter and others note, the max downhaul is bending that mast above the hounds to the max also, opening up that leech.

No Brobu that is not what I said. I said it is the top of the mast bending away to lee. This is NOT the same as the mast bending BACKWARDS under downhaul.

This characteristic is typical for wingmast on cats, something Petrucci pioneered on his A's in the past. And I really mean wingmasts here not teardrop shaped masts like the Hobie and Nacra variety. These wingmasts are very flexible over there minor axis and when the mastrotation passes a certain minimumal angle the top just bends of to lee. In some case even quite considerably. Skiffs (not wingmasts but very bending glass tops) have the same behaviour.

This is one of the funny aspect of wingmast rigs and great fun. You can finetune the whole rig with just the mast rotation. A little more rotation and the leech tension stiffens up the mast top and lifts your hull and gives you power. A little less rotation and quite quickly the leech tension is insufficient to stabilize the top and it bend off to lee with each gust. Thus spilling lots of air and make you accellerate without any lifting. The effect can be quite dramatic. On my own boat this is the way to totall calm down the vessel even in winds way beyond 20 knots.

>>Also, as mentioned, the mast rotation is minimal, so the related downhaul induced mast bend is on the long axis of that mast.

Although downhaul is important on wingmast rigs it is not all-important. Mast rotation becomes more important with increasing winds because of the way the top behaves. At least it is on my wingmast rig and I suspect that the 18HT are no different here.

Wouter