This page describes a simple, inexpensive way to make a sailboat steer itself using wind power. It was inspired by a posting by Al Gunther in the newsgroup rec.boats.cruising, and subsequent email between Al and John Ward. The following text and photos are courtesy of Al.
Sheet-to-tiller steering capitalizes on the simple principle that the same forces that cause a sailboat to go off course, are used to steer in a counteracting direction to keep it on it's desired course. When properly adjusted, there is an almost magical feeling that the boat is "on rails" as John Letcher described it in his book Self-Steering for Sailing Craft back in 1974. Most sailboats are designed so that the helm is balanced in light air, but weatherhelm increases as the angle of heel increases due to the force of the wind on the sails. This causes most boats to round up into the wind so the rudder is used to keep the boat on course. The same force on the sails that cause this rounding up, can be transmitted directly through a line and blocks to the tiller, to keep the boat on course.
The disadvantage of sheet-to-tiller steering is that there is no prescribed way to set it up to insure that it will work in any condition. The design of the boat, the choice of sails, the range of wind velocity, or the desired course, are all factors in determining which setup of the lines and blocks or the elastic is most likely to work. Success is therefore dependent on experimentation for a given boat. By observing how it works or doesn't work with a given setup and leverage or adjustment of elastic, one gains an intuitive sense that helps reduce the number of adjustments required to get it right. For a given set of conditions, I have found as many as four different setups using the exact same gear that could be adjusted to make the boat steer perfectly, so there is often no one best way and it's certainly not an exacting thing. I've always been fascinated by physics and I find the challenge of being able to self steer an enjoyable extension of sailing. Others, I expect are exasperated by this same aspect. This is probably the reason that sheet-to-tiller steering is not more widely used. But, for a coastal cruiser who already has an autopilot, or a cruiser with a limited budget, or even one who has a vane but would like to have a backup steering system that won't drain the batteries, this could be the answer.
To rig up the gear, you need a way to attach the snap hooks to the three blocks. I initially used a 10" length of the 1/4" line and tied bowline loops, so that is what is seen in the pictures. I have since replaced these with "D" shackles, which make a more secure attachment. A two foot length of line is needed for the elastic and a one twenty feet or so for the control line. Each needs a snap hook attached to one end with a bowline or an eye splice.
For each of the elastic pieces, bend the 4 foot length at the exact mid point and seize off a loop large enough to pass a 1/4" line through. Don't cut the elastic. Seize similar loops in each end. Now seize loops at the mid point of each of the two segments. Make a line loop through the last two elastic loops that you made, and include a snap hook in the loop. So now if you hold the line loop, there should be 4 strands of elastic attached. Two of these will end in a single loop and the other two in individual loops.
You need some attachment points on the boat. I just happen to have a handy tang at the end of my boom that the snap hook will attach to. My Catalina has side boxes which have teak cleats at the bottom. I drilled a hole through these on each side of the cockpit so I could attach a loop of line. This is a weak point and a good pad eye would be an improvement. I drilled and screwed the C-cleats to the tiller, one on each side so that they secure the line when pulled over the top and down. I found attaching them back about a foot from the nose of the tiller works good, and they are out of the way for hand steering. My aft pulpit has welded rings where the upper lifelines attach, which are a handy and sturdy place to attach the snap hooks.
My boom is mid sheeted on a traveler, which makes the mainsheet less convenient to attach the weather line to, so I attach directly to the boom. Since there is very little travel in the boom, I have attached a block at the boom. The windward line then runs from the aft pulpit to the block, back to a block at the pulpit, then to the block on the side of the cockpit, and then to the tiller. If the boom is end sheeted, attaching directly to the sheet would be the preferred method. The weather line needs to be adjusted so that it pulls the tiller to weather in gusts and the elastic needs to be strong enough to pull the tiller to lee in lulls. Add or subtract elastic lines as needed. The elastic line should always be adjusted to have zero tension when the tiller is just slightly to lee of center.
As a gust hits, tension on the main increases, pulling the tiller to windward, which keeps the boat from even starting to round up. This is an advantage over vane or autopilot steering. With vane steering, the boat first starts to round up, the vane or autopilot senses it, and only then turns the tiller to correct.
For close or beam reaching, it's the same as close hauled except you need to let the boom out far enough that the mainsail will luff when you head up too high. Let the jib out too, of course. These courses are more difficult to attain that close hauled and are less reliable if the wind strength changes very much.
Set the jib to draw best, but the main needs to be sheeted in quite a bit more than normal. I've had best results if the boom is sheeted in to less than 45 degrees off centerline. The trick here is to not get the windward control line too tight, only tight enough to steer to lee in gusts. The elastic needs to be adjusted to be barely strong enough to pull the tiller to lee, which pulls the slackened boom or mainsheet to weather when the main is on the verge of being back winded. If the boat surfs or you hit a lull, it will be moving faster than the wind and the apparent wind moves forward. When this happens the elastic should pull slightly to lee, steering the bow to weather and collapsing the jib, but exposing the main. This should only last a few seconds and it will recover unless a broach occurs. If that happens, chances are that it won't recover on it's own, and it's time to shorten sail. Reef the main unless you are down to the last reef and then you must furl the mainsail and steer by the jib sheet.
Attaching the windward control line to the jib sheet can be awkward due to the geometry. One way is to attach the first block to on the rail between the clew and the winch, the second block on the lee rail, the third on the windward cockpit loop. This was hard to set up on my boat so I rigged up the clamp with the first block as shown in the photo. The other blocks are back in the cockpit, the same as described above.
If the boat isn't steering properly, you have to determine why. Between gusts, the elastic should barely be stretched. In fact, in a lull, it should be slack and the tiller should be steering just slightly to weather. (Tiller slightly to lee.) If the boat rounds up in gusts, try tightening the windward control line. If this results in the boat steering too far to lee between gusts, then it's because the elastic is too stiff and you need to reduce the number or size of elastic strands. If it steers too much to lee in gusts, then you need to increase the number or size of elastic strands. The amount of purchase on the weather line can be increased or decreased by either using blocks or by the way the line is attached to the boom or sheet. This can be used to compensate for too little or not enough elastic.
I recommend starting sailing close hauled, as it's the easiest to adjust and the results are more obvious. It's easier to go from there to the other points, once you feel confident in steering close hauled.
Questions and comments about the steering rig should be sent to email@example.com. Correspondence regarding the web page should be directed to John Ward.
Al Gunther, Kingston, WA <---- 47° 52.7'N, 122° 30.9'W
"Self-Steering for Sailing Craft" by John S. Letcher