WIND VANE SELF STEERING
At our April Tech meeting, we were very lucky to have member Roselt Croeser once again address us – this time on wind self steering for yachts. As anticipated, Roselt acquainted us with the many alternative ways of achieving satisfactory wind vane self steering and the detail and refinement required to achieve this outcome. Members will remember Roselt’s previous talk on his junk rig developments based on a Spacesailor 18. This boat was also the platform for his experimenting with wind vane self steering.
Roselt commenced with some background on the early development of wind vane self steering. Early work was based on model yachts in the 1930’s and although there were earlier proponents as far back as Joshua Slocum it was not until the mid 1950’s that the principles were applied on full size yachts in the UK by Ian Major on Buttercup and Michael Henderson on Mick the Miller. The development of vane gear was also greatly boosted at this time by Blondie Hasler and the advent of the Observer Single handed Transatlantic Races which commenced in 1960.
Prior to this time, sailors relied on their yachts to be well enough balanced to steer themselves or they simply hand steered them for days on end. Alternatively, they may have used a rudimentary method involving the tying the sheet to the tiller. However, the development of wind vane self steering allows for much more efficient sailing under most conditions.
There is a good deal of reference material available on this subject and Roselt referred us to two books that contain the design principles and some plans; ‘Wind-Vane Self-Steering: How to Plan and Make Your Own’ by Bill Belcher and ‘Self Steering for Sailing Craft’ by John S Letcher. There are also numerous resources available on the web including http://www.faymarine.com/ – Paul Fay and http://www.jesterinfo.org – Blondie Hasler
With that background, Roselt launched into the more technical part of the presentation with the question;
Vanes – Vertical or Horizontal Axis?
The are two versions of vane – either vertical or horizontal axis and these in turn produce self steering by direct connection to the tiller or via one of two systems – either a trim tab or servo pendulum.
The axis or ‘stock’ for the vane may be vertical or horizontal. The vertical axis vane only moves about the vertical axis by the same amount (in degrees) that the boat goes off course. The vertical axis vane is probably simpler to construct but the adjustment requires some fiddly bits, usually a moveable pin in a wheel or a jam on a geared wheel. Notwithstanding, the vertical axis vane and trim tab steering system has served many people very well.
The horizontal axis system is a lot more sensitive because the vane can move through a much larger arc when the yacht goes off course. This movement can be up to 90 degrees both sides of vertical but is normally limited to 45 degrees. The axis can be laid back up to 20 degrees which makes the system more stable and achieves better results. The linkage can be line which is very simple but care needs to be taken to ensure it does not twist. Alternatively, a rod can be used. This requires use of some swivels and generally requires more engineering. Roselt noted that a right angle gear out of an old hand drill can be used for this purpose.
This system can also steer the tiller, trim tab or servo pendulum whereas the vertical axis vane can only steer the tiller or a trim tab.
In comparing the two systems, the horizontal axis vane is a lot simpler than the vertical axis and can be smaller, lighter and more sensitive than the vertical axis vane. The linkage on the horizontal axis system is simple if rope is used but requires some engineering if constructed with rod.
What do we steer?
The tiller direct connection requires a large vane and works best for a light tiller, particularly where the rudder can be balanced up to 20%. This was used by Acrohc Australis – the 12 foot boat that sailed around the world. Roselt has used this system on the Spacesailor 18 but it only worked into the wind and up to a reach because he found the vane was too small.
(Ed – notwithstanding its rudimentary nature, there are accounts on the web of ocean crossings apparently completed successfully using this form of self steering)
Trim Tab System
Trim tab systems comprise the vane and a counterweight equivalent to the weight of the vane. The rotating shaft of the vane is connected via linkages to a small tiller which moves the trim tab that is connected to the trailing edge of the transom hung main rudder. The trim tab tiller arm must be between the rudder stock and trim tab stock. If it extends forward of the rudder stock, this will result in positive feedback and the main rudder will slam across.
This system involves deploying some method to engage and disengage the vane stock from the trim tab stock and a method to lock the trim tab to the rudder to facilitate manual steering in port. Some of this function may be accommodated using the ‘course setting disk’ which deploys a pin or friction fit to adjust the course.
The trim tab system is not as powerful as other alternatives and the trim tab can get in the way but the system is very safe because the trim tab will just stall or create some turbulence if over steered and no components are likely to break.
This self steering system uses a horizontal axis vane to twist a blade suspended over the stern. This blade is able to articulate like a trim tab on a vertical axis but at the same time move in pendulum fashion through an arc (about 30 degrees each way) on a horizontal fore and aft axis. The servo pendulum is very powerful because it uses the pressure of water on the side of this rudder/oar blade to steer the boat and the water pressure is many times more than the air pressure deployed in other self steering systems.
Servo pendulum systems have the advantage that they can be fairly small and balanced and can be made by the amateur. However, they involve very large forces and therefore must be much stronger than the other types. Their downside is that they pick up ropes and other debris and can be more susceptible to breakage.
It is always good to learn from those who have already done it!
When making your self steering gear, Roselt’s advice is to use good size pulley blocks and set the rope linkages up so that they are not too tight. The recommended bearing material is high density polyethylene. This is the same material as white cutting boards at home. For the vane, one option is to use just an aluminium tube frame with a ‘sock’ over it to form the vane panel.
And if you are not into your own construction, Roselt informs us that there are kits available that are simple and low tech to assemble. These include the Hebridean, a servo pendulum wind vane (details at www.windvaneselfsteering.co.uk). Your editor also found Holland Wind Vane at www.hollandwindvane.com/self-steering.
On the commercial front, other than those mentioned previously, the Fleming is a major long standing self steering gear brand that has rounded Cape Horn many times and works well on all points of sailing.
Roselt concluded that it is possible to make your own wind vane steering for not too much money. The product of your efforts does not require any electricity, is fascinating to watch work and can free you up to do many other things on a longer trip.
A big thank you to Roselt for another great presentation which, in this case, I guess whetted our appetites to examine the design and amateur building of a wind vane self steering system in more detail and get started on our own projects.