I've mentioned windvanes and autopilots a few times over the past few weeks. A comment in yesterday's blog reminded me that not everyone who reads this is a sailor and so, may not know the difference or understand how each works. So, although they're both explained in much more detail on various websites, here's my sort of quick and dirty explanation.
There are numerous brands and models and they differ in how they work somewhat but the overall concept is the same: keep the boat steering a course relative to the wind direction. If the wind direction changes, so does the course you're sailing. Obviously, these will only work right in places where the wind direction stays pretty steady for long periods of time.
We have a Cape Horn windvane, built by hand in Quebec, Canada. A very detailed explanation of how windvanes in general work, and how the Cape Horn was developed can be found here. And here is a photo of an installation similar to ours. I'm using this photo instead of the photos I have of the vane on Siempre Sabado simply because my photos all the show the blade in the "up" (storage) position.
The wooden piece hanging down into the water is the blade. The blue thing up on top is the vane. The vane is oriented so that the wind hits it on its edge, presenting the least amount of resistance. With the vane in this position, the blade hangs down parallel to the centerline of the boat. If the boat wanders off-course, the wind will hit the vane from the side, causing it to tip either right or left. This movement is transferred to the blade, causing it to tip (not turn) so that it's no longer aligned with the center line of the boat. When the blade tips, it pulls a line that is attached to the tiller which causes the main rudder to turn and bring the boat back to the point where the blade is straight down again and the vane is straight up and the boat is once again on course.
The best feature of a wind vane is that it requires absolutely no electricity to operate.
Again, there are various models but they all work on the same basic principles. They usually contain some sort of electronic compass. On our Autohelm, instead of setting the compass course on the windvane, you instead steer the course you want and, once on course, attach the autopilot to the tiller and hit AUTO. The autopilot then reads whatever heading it's on and adjusts the tiller by pushing or pulling it to maintain that course.
The downside of an autopilot is that it requires electricity to operate. When we're motoring, that's fine since the alternator on the engine is pumping out the amps. But, when sailing, an autopilot can be a pretty big drain on the batteries. It also takes a fair amount of strength to keep the boat on course as we can attest to from the times we've had to hand-steer.
However, there's another option which is sort of a hybrid. We haven't rigged it up yet but plan to soon. In the hybrid model, you use the autopilot in place of the vane on the windvane. This allows you to steer a compass course and, since the blade on the windvane is doing all the heavy work of moving the tiller, the autopilot doesn't have to work very hard. This saves on the amount of amps drawn. And, the autopilot should last longer since there is less wear and tear on the moving parts.
-No electricity required
-Steers a course constant to the wind, therefore, no sail adjustments needed.
-Can be kind of fussy to learn to use.
-Steers a compass course.
-Extremely simple to set up and use.
-Uses precious electricity.
-If they break, can be difficult-to-impossible to fix
There you have it, in a nutshell.