Windvanes 101—Crash Course in Selfsteering Systems
Engineering
The different principles presented cover practically all vane gears available today. As we have seen, some of these principles are not feasible because they do not solve the problem of the weak force of the air vane or do not provide a sufficiently powerful steering device to control the boat. As faulty design principles can be the reason for non-performance, so can faulty engineering of a perfectly sound principle.
The trouble in actually putting a vane gear together is that it will be subject to constant work, heavy wear,substantial loads and all kinds of abuse from the salty sea. At the same time it is supposed to transmit fickle signals and turn them into vastly more power for steering corrections. If you build the gear with only ruggedness in mind the heaviness of linkages and moving parts will make it as useless as a cast iron airplane, which may last indefinitely but will never fly. If you build too flimsily there will be a crash on take off. The secret in putting together a good vane gear is to realize that the air vane must be able to activate the servo device, even if its signals are just feather light. This is achieved by using good bearings and relatively light linkage. As the forces involved in this part of the vane gear are slight, you do not have to use excessively heavy construction.
Once the servo device is activated the forces and loads are increased dramatically, but now you can provide a lot of a strength as it is no longer a question of babying a fickle signal but of transmitting a powerful steering response. This may sound simple enough, but you can be sure that there are many vane gears with unnecessarily deficient performance in light winds and downwind, due to over building and friction in the air vane to servo device connections. If this part of the vane system does not move freely at the slightest touch the vane gear will not perform well, unless it howls.
Apart from this general design consideration a number of engineering aspects should be looked at closely in appraising a vane gear:
- Are the materials of construction durable, compatible and corrosion resistant? This is an extremely important consideration as the windvane self-steering is a mechanical gear with many moving parts, some of which are directly submerged in salt-water. Corrosion affects performance through friction, binding and excessive slop. The durability and repairability of the gear are very negatively affected by corrosion. In spite of this many vane gears mix incompatible metals like aluminum and stainless steel, even under water, for reasons of cheaper manufacturing costs.
- How sturdy and easy is the installation of the gear? Does the system readily adapt to different yachts (ketches, double-enders, outboard rudders, boomkins, etc.). Does the unit come with a custom designed and fabricated installation system, or do you have to figure it out yourself?
- Is the unit mechanically simple and free of service? Can it be taken apart and fixed on board with common hand tools? Are its materials available and easily repaired, even in remote places?
- Is the gear liable to get damaged? Is it protected from underwater impact by shear pins or a designed breakage point? If not, there may not only be considerable damage to the gear but also to the boat itself. It should be noted that most damage occurs during sideload which happens when a surfing boat broaches and suddenly goes sideways at full speed.
- How heavy is the gear? Excessive weight at the very end of the yacht is undesirable.
- Can the self-steering system be used for manual steering in case of a breakdown in the main steering system?
- Is it possible and easy to remove the self-steering or the underwater parts of it when they are not in use (in port, motoring for long periods, in extremely bad weather, and heaving to, etc. )?
- Does the steering device interfere with maneuverability, especially when going in reverse during docking and other maneuvers in port?
- Can the system be overridden or quickly disengaged in an emergency, when you need to shift instantly to manual steering?
- Does the system interfere with the use of the cockpit (lines and blocks to tiller or wheel)?
- Is it easy to service and repair? Does it have a good manual and spare parts kit? Have dissimilar materials been used in the manufacture of the gear? In this case you may expect corrosion of the gear which will make the gear difficult or impossible to take the unit apart.