Custom Windvane Blades

[markxengineerin]

I am using a Monitor windvane, and the larger plastic vane (not shown above) interferes with the new solar setup. The below images are not to scale, but I'm looking for feedback on the idea of having a shorter, wider vane to produce the same response as the original longer, thinner vane which I can no longer use.



The assumptions are
1) Wind produces torque on the windvane blade
2) The torque for a given wind condition is proportional to the exposed area * distance from that area to the pivot point
3) Nothing else about the shape of the blade matters

I will also need to be careful to match the weight of the blade as closely as possible to the original (I have not weighed them, but the heavy weather plywood one feels heavier than the plastic, from my memory) or possibly adjust the counterweight mass. This does not seem too difficult.

I was able to find a sheet of the corrugated polycarbonate locally, now have 4'x10' to use as raw material, and the plastic rod stiffeners to slip inside. I will probably make several variations of "shortened blade" to see what looks /works best.

As for the solar, bimini, dodger, etc interfering with the wind to the blade and causing problems, that's always a risk, but I didn't have any problems with the previous (smaller) panels, so hoping it works.

The backup plan would be to ditch the windvane at some apparent wind angles and just use autopilot, but I still have not figured out how to get the NMEA0183 wind direction out of my old B&G "network" wind instruments, despite the manual saying there is one. Tips on that welcome too, will probably make a separate thread w/ more detail

[Orion Jim]

The wind deflection caused by your solar arrangement makes it difficult to make an educated guess as to the suitability of your redesign of the air vane. I would first contact Scanmar and ask for their recommendations. They are very helpful and knowledgeable.
My method would be to get a half sheet of 1/8” ply and try two or three different designs and see what the results are in a variety of wind strengths.
In my experience the “large” air vane works best in all but a gale so if I were to trim the length I’d add the area lost to the upper portion as a starting point and increase the surface area as needed.

[markxengineerin]

Monitor never answered my email- and I don't blame them, I'm not the original owner of this windvane. Here's what I ended up with.




If they work, I will probably be more careful and make a more symmetrical version in the future. Only thing missing is some electrical tape to do the edge trim, will do green to match the hull

[markxengineerin]

To anyone who has this problem in the future- this shape works perfectly

[wholybee]

It would probably work better to keep it rectangular. The size is not critical, but it is important it not be too heavy. I have seen all sorts of dimensions and materials Plastic like original, thin plywood, and cloth with a lightweight frame. All seem to work fine.

I normally use the "light air" paddle, and only switch to the smaller one if wind nears 20 knots. I simply cut mine shorter to clear my bimini, still a bit longer than the small one, and of course wider. I noted no difference in performance. Good to about 2 kts apparent wind if my boat is balanced well.

[wholybee]

Also, surprising to hear no response. They have amazing support, even for used vanes.

[markxengineerin]

Yes, I was surprised as well, but no reason to follow up this time since it's working. The thought here was to try to achieve the same torque vs. windspeed and blade angle as the original, but at this point I agree with you, the system seems very robust and insensitive to the shape. Such a good piece of equipment and a joy to use.

[Windpilot]

Shorter and wider paddle the same weight will work fine.
I sometimes use a small tillerpilot instead of the paddle.
Upwind tight I have too much gear and full cover in cockpit, downwind when apparent wind is very little or even motoring it comes in handy.

[GRIT]

Well done!

We had an older Aries windvane with a similar problem, and similar solution. Congrats.

Cheers.
Paul.