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Windvane Self Steering
The purpose of a wind-vane self steering device is to allow the skipper to do something other than sitting at the helm. While this is not practical for most un-ballasted small sailboats, a self steering device is an essential tool for the cruising sailor. Graham has been testing the wind vane on his Core Sound 17 Mark 3 which has an excess of stability and is a perfect candidate for self steering. Following its success we have scaled up the mechanism which is built with modest tools and materials to work for larger boats up to 30 feet.
We are pleased to offer our wind vane design as a set of downloadable plans and instructional documents revealing all the dimensions and ratios used as well as recommended materials and construction methods for building this simple cheap and effective system at a fraction of the cost of an off the shelf system. Graham's design is based on his decades of experience building wind vane self steering gear since the 1970's and the tips and tricks for setting up a simple to build and reliable system are all conveyed here. The plans for our wind vane include full size templates for all the critical parts along with the dimensions and ratios used. A builder's guide covers recommended materials and things to watch out for as well as details of construction. All you have to do is adapt the system to work on your boats transom configuration. To learn more about our system and if it might be a good fit for you just keep reading.
How a self steering wind vane works. Short version.
The “vane” part in the air provides the input to the rudder. The upper part of the system (the input or vane) is rotated such that it points into the apparent wind once the boat is on course. When the boat gets off course, the force of the wind hits the side of the vane causing it to lean over or in some cases rotate which in turn produces a correcting movement on the rudder. This turns the boat back on course until the vane is once again back to a neutral location. The trick to this is getting the right proportions, feedback and ratios of the vane, rudder, trim tab and control linkages.
Our Design Requirements
1. Low Friction: The name of the game is LOW FRICTION with wind vane self steering devices. We accomplish this with polished stainless steel against uhmw plastic for a cheap and reliable low friction connection.
2. Kick-up Auxiliary Rudder: This was a MUST HAVE for our shallow draft boats and not a feature we have seen on ANY other wind vane designs with an aux. rudder. The rudder pivots on a pin at the top of the transom and is held down with a line on a breakaway cleat.
3. Trim Tab Control: The aux. rudder is controlled by a trim tab that is actuated by the movement of the wind-vane (the part in the air). It's mesmerizing to watch and works completely without batteries or power.
4. Adjustable vane: The wind vane itself pivots on a horizontal axis that is inclined slightly. This creates an important damping effect in the actuation of the tab so that as the vane tilts it loses power because its projected area decreases. This reduces “hunting” and oversteering and unnecessary oscillation of the input to the rudder.
5. Removable vane: As with most systems, the vane is completely removed or replaced in seconds and can also be tilted back to increase the damping effect for high winds or made more vertical for light air which increases power. It can also be swapped out for a larger or smaller vane in lighter or stronger conditions.
6. Adjustable from anywhere in the cockpit: With the addition of a control wheel we can spin the upper part of the vane assembly 360 degrees using a control line routed around the cockpit. This means we can make small adjustments to the direction of the vane from anywhere you can reach the control line.
-Note that there are features we did not incorporate but may be important to some. One such feature is an emergency tiller. This allows for the use of the auxiliary rudder if the main rudder becomes inoperable. We would certainly want this feature on an ocean going cruising boat. If you build the auxiliary rudder up to reach the top of the transom then this is not difficult to do. Our kick up auxiliary rudder makes this a bit more of a challenge but a tiller tube can be fitted to reach a socket without much difficulty.
How does our wind vane system work...“I love it when you talk technical.”
Our design uses a horizontal pivoting wind vane to control a trim tab on an auxiliary rudder. (n this configuration, the vessels main rudder does the heavy lifting of keeping the boat generally on course essentially acting like a fixed skeg when the wind vane is engaged. The main rudder and most importantly the sails are adjusted first to balance the helm and then locked off with a tiller clutch. The auxiliary rudder then keeps the boat on course with small adjustments using a trim tab to amplify the power from the wind vane.
A kick-up auxiliary rudder with a trim tab on Carlita.
But will it work on my boat? …yes but!
There are literally dozens of ways to control a boat using a wind vane. Here are a few put into a nice chart we found on one of the many commercially available wind vane self steering gear company websites. The most common systems are auxiliary rudder systems and servo pendulum systems. If you prefer a servo pendulum system or your boat is better suited for one then you can still use the vane assembly from these plans and simply adapt the lower unit however we do not show details for a pendulum in these plans. Servo pendulum gears can generate great power but they are not easy to build and come at a higher cost due to the stronger materials and complicated parts required. They also rely on additional lines and rigging running through the cockpit. We feel an auxiliary rudder or trim tab system offers the best all-around self-steering device for most boats especially for low cost and simple construction methods. A balanced auxiliary rudder can generate as much power as you need for most boats and has the benefit of being a redundant rudder in the event you need it. In addition, a super low power electronic autopilot like the pypilot can be connected directly to the trim tab or auxiliary rudder to steer a course while motoring for example.
We once installed an auxiliary rudder wind vane on a 45’ steel sloop one third of it’s way into a circumnavigation. It completed its way around the world even though the boat crashed onto a reef in Venezuela. The skipper shipped the auxiliary rudder while the boat pounded. After being dragged off the reef, and with the spade rudder inoperable, the aux rudder steered the boat to port where the main rudder and other damage was repaired. The owner said that the wind vane rudder which was equipped with an emergency tiller mount saved the boat.
The most cited disadvantage of an auxiliary rudder system are that they don't kick up and they require the construction and mounting of an extra rudder. Kicking up is an important feature and one we didn't want to give up especially for our smaller trailable boats. Our auxiliary rudder can be tilted completely out of the water when not in use. This is accomplished with some careful geometry and clever mounting BUT it is best suited for nearly vertical or forward raking transoms. You can still fit an auxiliary rudder to a transom with reverse rake but it is typically done with a very strong vertical tube bolted to the transom at the top and bottom with braces extending diagonally low to the waterline for support. This requires some complex geometry and custom mounting brackets so it is a bit more challenging to mount. If you are fitting a wind vane self steering system to a boat with an existing transom hung fixed (non kick up) rudder then a trim tab added directly to the main rudder may be a better solution for your boat and our wind vane would be easily adapted in this case.
The real challenge of mounting. “No size fits all.”
Production self steering units will supply various kits and tubing and brackets to help make their systems fit your transom with just a few bolt holes carefully placed. Even with those systems it's up to you to mount it correctly and this will be no different. You will, without a doubt, need a custom mounting solution for your boat and you are the best person to design and build it! The system we are offering here is but a single example of a configuration fitted to a vertical or forward raking transom of our own design. We can’t help everyone mount this system to their individual transoms and there are probably some sterns that will really be challenging. You may need to design your own rudder for example using the parameters and ratios we offer in our plans as a guide in order to meet the needs of your transom configuration. This is for you to figure out! Remember, being a D.I.Y’er (also known as a sailor) is all about saving money by not charging yourself for the time it takes you to do stuff!
Limitations of a mechanical self steering device...What’s the “Ketch”?
Wind vanes are not for everyone and one you build yourself has its own unique challenges to boot. A mechanical wind vane cannot blindly follow a compass course but instead must follow the ever-shifting wind direction and balance of the boat as wind and seat state change. On very fast boats, the apparent wind direction shifts so much that a wind vane is somewhere between useless and dangerous. Cruising cats can be fitted with wind vanes but typically an electronic autopilot is more practical due to their higher speeds. A mechanical wind vane relies on the wind speed being greater than the boat speed which for the vast majority of cruising boats is usually the case. On the current crop of large single handed around the world racers, automatic pilots have become so sophisticated they require training of the computer as they learn the boats behavior during high speed breakaways.
If you are travelling at displacement speeds with a bit of surfing thrown in and if you do not have unlimited power and money and if you do not mind making small adjustments to the boats trim and self-steering gear as the wind shifts, you will have a loyal assistant that never grows tired or needs feeding.
Staying in trim
A good sailor keeps his boat in trim and a happy wind vane is one that is sailing a boat that is already balanced as well as possible. If your boat is heavy on the helm already then you may need the extra power provided by a servo pendulum system. If you have a hard time steering your boat, a wind vane (any wind vane) will too.
Space requirements
Highlighted below on Graham's Core Sound 17 Mark 3 'Carlita'. Our design requires open space above the transom so it won't work on a standard Core Sound 17 for example due to the proximity of the mizzen sheets. The addition of a boomkin allows the mizzen sheet to be behind the reach of the wind vane sail in the case of the CS-17 Mk3. Likewise a yawl with long mizzen boom will be a challenge as the mechanism must be mounted far behind the transom.
A few notes from Graham....
"Horizontal axis vanes and servo pendulum paddles are the most powerful self steering systems and are certainly required for large or heavy handed vessels. Carlita is a light well mannered boat and requires finesse rather than brute force. If you have not already seen the self steering video, check out the video and answer your own question. She is running almost straight downwind and surfing. After this video was taken she surfed to a little over 10 knots without misbehaving."
Above, Graham steering his then unpainted Core Sound 17 Mark 3 Carlita with all sails flying in the 2016 Everglades Challenge. Note that this earlier version of the kick up wind vane employed a vertically pivoting vane which was converted the more recent version afterward. Vertically pivoting vanes have less power but do offer some advantages such as being able to just point into the wind when not in use. (photo Patrick Johnson)
Graham continues...
"The key is an ultra light vane and very low friction. The lead counter weight is just 6 oz on Carlita's system. to balance the vane. This makes the vane very responsive and reduces friction and lowers the mass moment of inertia. The next important feature is differential feedback in the linkage. This means that when the vane kicks the servo tab over and the tab turns the auxiliary rudder, the angle of the tab is rapidly reduced. If you do not have this feature the boat will hunt badly down wind where there is no natural balance from the sails as you do when close hauled. The whole thing is a delicate balance between power and feedback."
In the video below, Graham sails Carlita a Core Sound 17 Mark 3 with the wind vane rudder disabled and in the "raised" position and the boat steers herself with proper sail trim to windward. Notice that the tiller is simply lashed.
"I want the rudder fixed to aid directional stability. Before engaging the vane, I try to find the sweet spot for the rudder and lock it. I will then observe the course after the vane is engaged for a while and I may rotate the vane or move the tiller slightly. Usually I adjust the vane first. It is a powerful little vane and will tolerate a fair amount of imbalance. All self steering systems hunt but the better everything is balanced the less oversteering there will be.
If you do not enjoy fiddling then a wind vane may not be for you. Naturally they are worthless in waterways because the wind is too shifty. But It did do a great job last week running down the Cape Fear River. The GPS showed a top speed of 8.75 knots and the speed was rarely under 6, at least 3 knots of that was current." -Graham Byrnes