Canting mast

[casavecchia]

Hi all,
I originally posted this article in the Australian Moth Forum so you may already know it. In fact it is of no interest for Moth sailors because they tilt the whole boat to windward but can work well on boats that are designed to sail heeled to leeward such for instance trimarans.
Last year I built and tested on my small trimaran a free standing canting mast . The concept is really simple though unusual and worked very well.
It only works with unstayed masts, because the mast tilts from one side to the other every tack.
The tube in which the mast is stepped is raked aft 10 degrees. The mast has a built in 10 degrees kink toward the bow just upper deck level . This bend in the mast compensates for the rake of the mast socket so the mast stays vertical. This happens only when the boom is perfectly centered. Boom gooseneck must be a bolt through the mast so as the boom swings out the mast rotates and the part of mast over the kink- that is from deck up- swings to windward and aft until when , with the boom squared, you end up having the mast tilted 10 degrees out of the vertical on the opposite side of the boom and 10 degrees back. The mast I used was a beefed up carbon windsurfer mast. I made only the lower part, the part with the bend, and joined the two parts together. And that’s all. Try to figure how it works using one of those kinked plastic straws boys use for sipping Coke. Cut the part under the bend short so simulating the part of mast that fits into the socket and pivot it between thumb and forefinger.

Advantages

Less windage than a stayed mast
Lift upward from the rig
Mainsheet pull lessened ( I use no purchase on a aft bridle mainsheet) because the sail is compensated as the axis of rotation crosses the sail.
Easier jibes as the center of effort of the sail is near the center line
More exposed sail when the boat is heeled to leeward

Disadvantages:

Less adjustable rig than a stayed mast
Need for a stronger (and heavier) structure in way of mast socket. But my next boat will have a stump on which rotate the mast that will “grow” from the boat itself I hope lighter and stronger than conventional Laser style socket.
Pumping on mainsheet is somewhat less effective
In very light air is more difficult shaping the sail by gravity because you can’t heel too far the mast to leeward.
Comments?
Marco:

Marco, very interesting! I saw an rc model called the "Mickey Finn" about one meter LOA with a mast done exactly the same way.
Never saw one sail but always thought it was a cool solution on rc boats where it would reduce the load on the mainsheet making the use of a smaller winch possible thus saving weight, power consumption etc.
Any pictures of your setup?

[casavecchia]

Hi Doug,
for the photographs go to www.diecipiedi.it than click
"foto e video" than "2004" than "Nero Cirla" and "Marco Casavecchia" (incidentally "dieci piedi" means "ten feet").
Theese two boats have the bent canting mast.
You will notice that they always have the mast square to the beam or more to windward. This is not immediately apparent because the kink of the mast is 10°and is more apparent when the boom is squared.
I think this 10° measure is very critical: less and you have no effect, more and you feel the maisheet slack and probably you get an oversheeting effect.
Check Phil Stevenson answer to my post on Aust.Moth Forum under "canting mast".
Marco

[nico]

http://www.diecipiedi.it/foto%20Marco%20Casavecchia.htm
http://www.diecipiedi.it/foto%20Nero%20Cirla.htm

[SeaDrive]

See: http://www.stadtdesign.com/products/SwingRigIntro.htm

[casavecchia]

That's simply great!
I made the first canting mast about seven years ago and always suspected that was a good idea!
I noticed that John Perry too made a similar mast for his
foiler trimaran but may be for different reasons.
Nothing new under the sun, as we say in Italy!
Marco.