Went for a sail on the 18m proa today. The boat has been out a few times since my previous post but nothing spectacular.
Forecast today was for increasing winds to over 20kts but that did not happen.
During the sail, wind built from flukey conditions with zephyrs to maybe 3kts. By the time we were heading home the wind had built to steady 5 to 7kts with occasional lifts to 10kts.
So the lesson for today was light weather sailing. Trying to sail with wind over the ww hull inevitably resulted in getting locked in irons. I have determined that the boat needs to be above 2.5kts for the rudders to produce enough steering moment to counter the weather helm caused by the offset drag from the ww hull.
Sailing with the ww hull on the lee side creates lee helm and enables speed to pick up and then pinch up safely without risk of getting into irons. I was quite surprised by the VMG in comparison to other boats; cats and monos near us, in the flukey conditions. We sailed as high and a little faster when in the groove. These were cruising boats though not racers.
We have mastered the art of turning within the limitations of the uni-directional rudders by doing a partial shunt - backing the sails by swing the boom around, going in reverse until the required angle for the new tack is achieved and then sailing off on the new tack. It certainly indicates the boat will shunt easily once the rudders are fixed.
The hull was roughly cleaned two weeks ago and there has been a small improvement in speed/wind ratio. Today we peaked at 8.5kts in wind never above 10kts. Best speed was with true wind at 90 to 100 degrees.
The sails can also be set reasonably well now. Major improvements have been lowering the point of anchoring for the main luff within the boom and installing running back stays to the trailing end of the boom that can tension the jib luff.
Next week the boat will be slipped for proper cleaning and new antifoul. Gearboxes will replace the chain for operating the rudders. This will enable continuous rotation and a second wheel will be added to enable rudders to be operated independently.
Another observation when sailing on the lw hull is that the helm required to counter the weather helm actually contributes to the leeway. With independent rudder operation the leading rudder can be set slightly to weather and locked to resist leeway and steering achieved solely with the trailing rudder, which will have to work harder but will actually resist leeway as well. Once this is done the value of the centreboard will diminish.
Rick Willoughby
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