In the video of the OW10 Moth sail I said I would report on its performance, so here we go.
The OW10 was designed in response to the hype of getting the power down low, theoretically having the power but be easier to manage. So a shortening of the rig by 300mm pushed the boom length out buy a further 250mm to maintain maximum sail area but lowering the COE. The sail design was the same as the OW9 except for the difference in aspect ratio so a direct comparison could be made in testing the effect of lower aspect.
In testing we found that in lighter conditions the boat would get onto the foil in just the same manner so overall power was ok, but the rig/boat would come back over you in lulls more quickly due to the power being lower, so at that moment acted like a small sail.
In medium more consistent conditions the sails were very even, except that initially the OW10 felt a bit more bound up. We had kept the hounds up at the same height as the OW9 so you could use the same set of stays, but then lowered the hounds 300mm (now the same distance from the tip) and lowered the spreaders 150mm producing same softer head support as the OW9 and gust response improved to the level of the OW9.
In heavier conditions with the sails flattened off (heads flat and feathering) the OW10 did not depower as well as the OW9 as the longer boom meant you were actually left with a bigger area of sail left with power. So too much power is too much even down low.
In the end we cut the foot length of the OW10 down to the same as the OW9 and faired the leach though to the head which meant we now had a smaller sail which was easier to manage top end, not rocket science in the end. The cut down OW10 is surprisingly efficient coming down the wind range and is now available as the OW12 7.7m2 area small sail.
So, for Perth conditions, ( ie: the Worlds 2019) what do I recommend?
– sailors 75kg or less, the OW 12 will probably be your main choice for the usual windy seabreezes at that time of year. But you’ll want the full size OW11 as well for the light days.
Heavier sailors, over 75kg will be happy tearing around on the OW11, but if it blows over 25 knots and they keep racing, it will be handy to have the OW12 in your quiver.