Opua: sheet to tiller self-steering
Opua: sheet to tiller self-steering
A reader in Cape Town, who owns a Sentinel Explorer, a very pretty boat that looks something like a sloop rigged Drascombe Lugger, wrote asking for more information about the sheet to tiller self-steering system I used on CHIDIOCK TICHBORNE I and II. I thought some of the rest of you might be interested as well.
I also used this method to steer EGREGIOUS for about 10,000 miles from the point where the Aires vane was broken south of Australia all the way back to San Diego, with stops only in Auckland and Tahiti.
I by no means am the originator of this system. I first read of it in an article in a sailing magazine in the early 1970s and then in a book, SELF-STEERING FOR SAILING CRAFT by John Letcher, which is still available used from Amazon.
I haven’t read Letcher’s book for almost forty years. It is mostly about how to make your own self-steering gear and convinced me that I didn’t want to. Only one chapter--the third if I remember correctly--is about sheet to tiller self-steering.
While there are several variations, I used essentially the same one on both CHIDIOCK TICHBORNE, an 18’ yawl rigged centerboarder displacing 900 pounds and EGREGIOUS, a 37’ cutter displacing 16,000 pounds.
On CHIDIOCK TICHBORNE I used the jib sheet. On EGREGIOUS the staysail sheet.
In both cases the sheet is run aft first to its normal lead block on the leeward side of the deck, then crossed over to a block on the windward side of the boat, and then to the tiller to which it is tied. This last block should be positioned so the line approaches the tiller at approximately a 90º angle. The force of this sheet is balanced by shock cords/bungee cords on the leeward side of the tiller.
That basically is it. Minimal expense and easy to set up. The key, as with everything about sailing, is balance, and obviously friction must be eliminated from the run of the jib sheet as much as possible. More blocks may be necessary to rout the sheet around deck obstructions, although I never needed more than two: the normal lead and one additional.
I tied the sheet to the tiller with either a slippery hitch after taking a couple of wraps around the tiller, or a clove hitch.
Just aft of where the sheet was tied to the tiller, I also tied a thin line around the tiller with a clove hitch in the middle and then tied the ends together in a series of four small loops, each with a diameter of a couple of inches/5 centimeters, as attachment points for the shock cords to enable me to vary the resistance the cords provided depending on wind strength. I used square knots to make each loop. The other ends of the shock cords were hooked into loop around a cleat on the edge of the cockpit on EGREGIOUS and the boat on CHIDIOCK TICHBORNE.
Sometimes on both boats I would have as many as four shock cords hooked up. Sometimes only one. Sometimes I would have all hooked into the loop closest to the tiller to provide maximum resistance; sometimes one in one loop and one in another; etc.
What you are seeking is to have the boat sailing on the course/point of sail you want with the helm amidships. Sometimes the jib might have to be trimmed flatter than it normally would be. Sometimes fuller. This is a matter of experimentation; but getting it right is not difficult on a properly designed boat.
I found on both boats that it was necessary to have at least part of the main sail set. CHIDIOCK TICHBORNE sailed very well under jib and mizzen, which were of equal size of 30 square feet. But sheet to tiller wouldn’t work with only jib and mizzen set. Leverage from the mainsail to bring the bow back up toward the wind was necessary.
Also this system only worked from a close reach to a broad reach.
This is not a bad thing. Every boat I have ever owned will self-steer to windward with the tiller tied down and the sails properly balanced. And sailing dead down wind is always inefficient. I sometimes do it with a spinnaker set; but gybing broad reach to broad reach is usually faster.
The forces you are trying to balance are the jib pulling the bow off the wind and the mainsail and shock cords bringing it up into the wind. In practice in consistent wind, the system steers a good course.
All self-steering systems are subject to changes in wind force as well as wind direction. Sheet to tiller requires more frequent adjustment than wind vanes or autopilots when the wind increases or decreases in strength.
I never had need to use sheet to tiller self-steering on RESURGAM or yet on THE HAWKE OF TUONELA, although I have the necessary blocks and shock cords aboard and have on my eternal “to-buy” list a small sail for self-steering. I think the jib deeply furled would probably work. The full jib would be too powerful. And a smaller sail set as a flying staysail would be better.
Sunday, April 18, 2010