Sheet to Tiller Self Steering

Introduction
There is no experience like an off-shore passage on a small sailboat.  As land fades into the horizon, you are left as a lonely witness to the ever changing temperament of the ocean surrounding you.  Time slows down and you keep up with enjoyable or necessary activities such as reading, writing, thinking, repairing, navigating, or sailing. That is as long as you don't have to steer.

The Art of Self Steering

Steering is a continuous chore that must be preformed regardless of the weather, the point of sail, or the time of day.  It will bog you down, bore you to tears, and rob you of countless hours of leisure in a beautiful open ocean.  It can be overcome but most methods are expensive and are prone to failure.  A self-steering wind vane is the best option for most cruisers given that they perform well on most points of sail, require no electricity, and are made of robust metal parts.  The downside is they can cost up to $5000, and if a part fails, it may be difficult to repair or replace.  The second option is the electric autopilot.  The downside here is a $600-$2000 price tag, 1-30 amp energy consumption depending on sea conditions, and a high failure rate given that most units are undersized for the boat they are installed on.  The third option is a sheet to tiller system which uses a line directed through a series of blocks to divert the power of the sails and keep the boat on course.  This system uses no electricity, is easy to repair on land or at sea, and costs virtually nothing given that the required parts are standard inventory on most sailboats.  The system requires more time to set up and adjust than the self-steering wind vane or electric autopilot but will result in a better understanding of your boat and the forces that propel her.

Our Westsail 32 sailing herself from Bermuda to Guadeloupe

Required Materials
- 6 blocks attached to swivel snap shackles.  Snap blocks are preferred but standard blocks work also.  Regardless, it's always nice to have extras to help run lines.
- 1  30 ft length of 3/8" low stretch line with a swivel snap shackle attached to one end.  As I explain how the system works, I will refer to this line as the steering sheet.
- 2 cam cleats mounted on either side of the tiller approximately 36 inches from the tiller pivot axis.
- 1 Four foot length of 3/8" O.D. 3/16" I.D. surgical tubing to make the counter balancing bungy. You will have to form this tubing into an "M" shape and create loops at every end and corner with sailing twine.  Permanently attach a swivel snap shackle to the two corners at the top of the "M".  This shackle will be used to attach the bungy to the stern pulpit or toe rail.  Take a 4 ft section of 3/8" line with a swivel snap shackle at the end that can be quickly attached to one, two, or all three loops at the bottom of the "M".  Then end of the line will go to the cam cleat mounted on the tiller while the snap shackle allows for quick adjustment of the pull provided by the surgical tubing.  I will refer to this assembly as the bungy.

Materials Needed for Bungy Assembly

Form Tubing into "M" Shape

Create Loops with Sailing Twine

Loops Located at Ends and Corners at Top and Bottom of "M"

Top of "M" Connected to Snap Shackle
Bottom of "M" Connected to Shackle and Rope Lead

View of all Required Materials

Additional Materials for Wing on Wing Sailing
- Additional 30 ft length of 3/8" low stretch line with swivel snap shackle attached to one end.
- Homemade jig for attaching to genoa sheet.  Jig is made of plywood, one sheave cut in half, and one half of a cam cleat.  See drawings for more details.

Jig for Attaching to Genoa Sheet

Jig for Attaching to Genoa Sheet

The Boat
I have successfully experimented with sheet to tiller self-steering on both a heavy displacement full keel mono-hull as well as a light displacement dagger board trimaran.  I do not believe displacement or keel configuration alone are determining factors on whether or not sheet to tiller will work.  The important thing is that your boat is balanced.  A balanced boat will have slight weathered helm when sailing closed-hauled or on one of the three reaches.  Try letting go of your tiller the next time you are out sailing.  The boat should slowly head up wind.  If the boat heads up quickly try sheeting in the head sail or increasing its size relative to the main sail to create more lee helm.  If the boat falls off try sheeting in the main sail or increasing the size relative to the head sail to create more weathered helm.

Do not be afraid to reef the mainsail or the head sail to achieve a balanced helm.  Most boats are designed for optimal performance in light wind conditions.  You would be surprised how quickly some designs get overpowered as the wind increases.  Another option is to adjust the size/depth of the keel or center board.  As a boat heels weathered helm increases.  Adjusting the keel may increase or decrease this effect if sail adjustments alone aren't cutting it.  As with sailing in general. Self-steering is all about trial and error so do not be afraid to experiment.  If you are unable to balance the helm on your boat, it is unlikely any self-steering system will be successful on your boat.  Once you have achieved a balanced helm, it's time to make the connection between tiller and sail.  There are a variety of ways of doing this and the best choice will depend on the point of sail, configuration of the sails, and personal preference. I will discuss three basic methods of rigging a sheet to tiller system including setup, theory, and practice of each method.

Mainsail Sheet to Tiller

Setup
The simplest method in terms of setup is the main-sheet to tiller system.  Run a line from windward side of the stern pulpit or toe rail to a block on the boom and back to the windward side directly opposite the cam cleats on the tiller.  The line is then run over the tiller and engaged within one of the cam cleats for easy adjustment.   Directly opposite on the leeward toe rail connect the bungy with the rope lead run over the tiller and engaged with the other cam cleat. This system works best on close hauled or close reach points of sail.

Main-sheet to Tiller Setup

Theory
The main-sheet to tiller system works under the principle that increased pressure on the sails causes the boat to heel, which in turn causes more weathered helm.  Increased pressure on the sails can result from slight variations in the course as the boat moves through the optimal angle to the wind given its current sail trim.  Additional causes include variations in wind speed, a.k.a. puffs and lulls.  Regardless of the cause, as the pressure on main increases the boom will move to leeward resulting in the tiller being pulled to windward via the steering sheet.  The boat will then fall off away from the optimal angle to the wind and the pressure on the main will decrease.  The bungy should be set to pull the tiller back to center or slightly to leeward as the boat falls off.  This will result in the boat's natural weathered helm slowly bringing the boat up again until the cycle starts over.  The boat will effectively sail a slight "S" pattern thru the water as the balancing act between weathered helm, sail pressure, and the surgical tubing plays out.  Adjustments may need to be made to achieve this balance.

Slight "S" Pattern Course being Sailed

Practice
To engage the system begin by sailing the desired course and trimming the sails accordingly.  Then engage the bungy to pull the tiller to center or slightly to leeward as mentioned in the theory section.  Engage the tiller sheet to mimic the pressure you are applying to keep the boat on course.  Let go of the tiller and watch what happens.  Use a landmark or the compass heading as a reference as you watch the boat sail the "S" pattern.  Make small adjustments in the tiller sheet and bungy to keep the boat on the desired course.  Tweaking the sail trim also serves as a means of fine tuning the system.  Slowly easing the main sheet while leaving the tiller sheet fixed allows for small adjustments on the tiller sheet tension.  Additionally, adjusting the head sails will also affect the balance of forces keeping the boat on course. The precise effect of sail adjustments on the performance of the system depends on the boat.  It may be necessary to experiment with different adjustment approaches.

Stay-sail Sheet to Tiller System

Setup
Run a line from the mast step to a block on the stay-sail clew and then through a series of blocks acting as fair leads along the leeward toe rail back to the cockpit.  Lead the line across to the windward side directly opposite the cam cleats mounted on the tiller.  The bungy should be mounted on the leeward side of the tiller as before.  This system works best when sailing on a beam or broad reach but may also work when sailing up wind.

Stay-sail to Tiller Setup Forward 

Stay-sail to Tiller Setup Forward as seen from Cockpit

Stay-sail to Tiller Setup Aft

Theory
The stay-sail sheet to tiller system works under the concept that as the boat falls off the head sail gets blanketed by the main sail and looses pressure.  When the stay-sail is full, pressure on the steering sheet will pull the tiller to windward and cause the boat to fall off.  As the mainsail begins to blanket the stay-sail, the bungy will pull the tiller to leeward and cause the boat to head up.  This will keep the boat sailing an "S" pattern in the desired direction.  The stay-sail sheet to tiller system may also work when sailing up wind, however, the governing forces will resemble those discussed in the main-sheet to tiller system.

Practice
Manually sail the desired course with the appropriate sail trim. Engage the steering sheet to mimic the pressure required to keep the boat on course.  Observe the course and make small adjustments in the steering sheet and bungy.  If the boat is unable to stay within an acceptable course range, sail adjustments may be necessary.  First try adjusting the stay-sail sheet as a means of delivering more or less play on the tiller.  If that doesn't work, try adjusting the main-sheet.  I have noticed that when sailing on a broad reach, very small adjustments in tiller sheet tension or sail trim will suddenly make the difference.  My advice is to keep experimenting and studying the boat's reaction.

Wing-on-wing Sheet to Tiller System

Setup
Run a line from the stay-sail to the tiller as mentioned in the setup portion of the previous section.  Run a second line from the poled-out genoa sheet through fair leads along the windward side of the boat back to the cockpit and then across to the leeward side of the tiller.  Connecting the second line to the genoa sheet offers its own set of challenges.  See means and methods of doing this in the required materials section.  You should be left with two steering sheets that are pulling the tiller in opposite directions.

Wing on Wing Self Steering Setup Aft

Wing on Wing Self Steering Setup Forward

Wing on Wing Self Steering Steering Sheet to Genoa Sheet Connection

Theory
When sailing wing on wing with two head sails, one of the head sails will always have more or less pressure on it than the other sail depending on slight course variations or passing waves.  I used to tell my sailing students when sailing wing on wing, always point the tiller to the collapsing sail to keep the boat on course, which is what the sails will do if properly rigged.  When the boat heads up and the poled-out genoa begins to collapse and pressure on the stay-sail will increase.  This will pull the tiller to windward and cause the boat to fall off again.  If the boat falls of so far that the stay-sail collapses, pressure on the genoa will have increased, which will pull the tiller to leeward and cause the boat to head up.

Practice
The setup is the most difficult part of this self-steering system.  Once you have achieved that, it's simply a matter of sailing dead down wind, letting the sails out to catch as much wind as possible, and tensioning the two steering sheets.  Small adjustments in the sail trim or steering sheets may be necessary as before.  It may also be necessary to roll up a portion of the genoa in order to achieve the appropriate balance between the larger genoa and the smaller head sail.

Sources
https://www.blueanarchy.org/selfsteering/
http://www.jsward.com/steering/