On Sat, Oct 17, 2009 at 12:48 AM, Luca Antara <luca.antara@
> For a boat that is still at the design stage (at least for the masts, sails and rudders) I >can see three possible CofE solutions that could change the dynamics of shunting. The >first is the obvious one of having a larger jib and smaller main, but this would not work >with a Ballestron rig if the Cof E became forward of the mast, and anyway, Rob has >indicated that the jib is already quite difficult to raise.
The jib is easy enough to raise, but difficult to set well on the
unstayed mast. Not a problem for most cruisers, but not ideal for
racing, particularly upwind in a breeze when the excess luff sag is a
nuisance.The second is to have a wing mast which should bring the CofE
of the main forward (same possible problem as solution 1 with the
Ballestron rig).
> The 3rd is to have 2 masts. I have never shunted a proa but from my windsurfer experience moving the mast (and therefore CofE) fore and aft, it should go like this.
>
> While heading upwind a little, let go the fore sail sheet and there will be a tendency to luff up more as the CofE has temporarily moved way aft.
> Let go the aft sail sheet and sheet it in immediately as the fore sheet in the new direction, which gives a temporary CofE way forward.
> Sheet in the new aft sail once up and running.
>
> Other benefits of 2 masts could be the ability to move the CofE at will by sheeting in or out the aft sail and thereby reducing the load on the rudders. In theory one might be able to take the steering load completely off the rudders and steer on a reach with just with the sails, as with my windsurfer which obviously has no rudder steering.
> Does anyone (Rob,Doug?) have a proa with 2 masts that can verify or disprove this?
On Elementarry with two sails, the shunting was as you describe.
Sheeting in the rear sail was very easy as it was being blown in by
the front sail. Because of this "blown in" effect, easing the rear
sail hard on the wind did not make much difference. It works on the
centreline and stops working pretty much as soon as it is eased. More
effective on a reach, but I don't remember ever sailing it without the
rudders.
I have sailed the una rig without the rudders. Sitting aft on the lee
hull it is possible to get about 45 degrees either side of ddw.
Higher than this and the lack of weight to windward becomes a problem.
I have not tried it two handed. Upwind (getting off a shallow lee
shore) it is easy enough to sail a series of swoops. Sheet in the
main while sitting as far aft as possible and the boat does a big
looping luff. When it is head to wind and almost stopped, change ends
and haul in the main quickly and you do a big swoop the other way. 3
or 4 of these and you are 100m offshore.
I changed from schooner to una becaues I did not have enough hands and
feet to sail it solo, the pocket luff sails made it very hard to right
and because in Perth I often sailed in 20 knots plus which made it a
real handful solo. I stayed with the una rig because it worked so
well, first with two rudders at 25% of loa, then one, then two at 33%
and finally one at 33%.
regards,
rob
> Also from my windsurfer experience, I had theorized that the CLR could be moved aft by raising the fore rudder but this does not seem to work for BD.....
> Cheers,
> Robinho (mech.eng. windsurfer).
>
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