The kite proa is steered without rudders by shifting the towing point of the kite. It works when sailing on the wind but not downwind.
We stumbled on the possibility of doing something similar on the 18m proa when we first tested the dagger board. The second time out with it, the loads on the board were quite high and a but weld holding the shear pin tab failed allowing the board to swing backwards. We did not realise this until we did a shunt. Boat was almost perfectly balanced when the board was trailing at about 35 degrees off vertical thereby shifting the CLR aft of the CoE to counter the natural weather helm caused by the drag of the ww hull. That was on port tack.
After shunting, the boat kept going into irons on starboard tack because the board is pivoted about one edge rather than mid chord causing it to hang forward creating large unbalance in that direction.
So there is the possibility of steering the boat when it is on the wind with fine control on the swing angle of a deep central dagger board. It would not be possible to turn the boat using the same method when running or motoring.
Turning a centrally mounted rudder would not cause the boat to change direction but rather just crab sideways.
On 07/09/2015, at 10:05 PM, "robriley@rocketmail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
Id be interested to hear if anyone has contemplated a centre mounted rudder instead of twin rudders
Just a couple of points:
Essentially this rudder would still need to kick up if contacting anything like grounding
Most of the things that apply to the current system design are the same
But it would mean there was only one rudder to accommodate
This has sort of been done on monohulls before, as there have been long keel boats like Dragons which have the rudder mounted on the keel, although presenting quite short moment arm for the rudder. And there have been fin-keel boats with trim tabs on the aft end of the keel. The difference here is that the boat needs to travel in both directions, so it cant have that preset lead condition between the centre of effort and the centre of lateral resistance. Well unless the wind is on the forward quarter or it rocks the rudder aft when the boat changes direction in a shunt.
So I would be interested what people thought or if it had been tried.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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