how protect vane in a windvane

[Suijin]

Lift would not be good on a wind vane. You can be sure that most producers, and I’m sure Scanmar, tested them and found flat “foils” gave the best response. Remember, in a servo pendulum mechanism the foil needs to exert not much force. You don’t want a wing “flying” in the airstream, you want a paddle that gauges and responds simply to wind direction.

The swim paddle on a monitor has a NACA foil, so they are clued to foils.

[model 10]

[QUOTE=wingssail The force produced by the wind which pushes the vane over is lift.

No it's not. Just like the trim or servo tabs on an aircraft control surface, it's not an airfoil. It's only purpose it to deflect and change the pitch of the servo rudder. There is no need for lift or drag.

[Snowpetrel]

lift is lift, a flat foil produces lift until it stalls, then it produces more drag and less lift. A proper foil shape produces more lift for the area and delays stall. A windvane is not a Trim or Servo tab, they are generally part of the foil. The reason for flat foils is simple, they work well enough, they are cheap, and they are light. A foil section should work better, at the expense of more complexity, and a foil may have the disadvantage of producing too much lift in stronger winds.

[steverino333]

Does anyone,preferably in south Florida have experience with a voyageur windvane?

[Triumphant]

The Hydrovane does not use wood as a wind vane!!!

[Snowpetrel]

Originally Posted by sardinebreath

Seems counter-intuitive that a heavier vane would be more sensitive in light wind. Surely initial movement is going to be greater the lighter the vane. I suppose putting weight at the top of the vane would help counteract resistance of the counterweight, but only once the wind had managed to knock the vane off vertical--and that is going to be more difficult the heavier the vane. But I accept data supplied by experience over my own abstract conceptualizing so I reckon I will try the weighting thing once I get a vane and am wrestling with light air performance.

The real issue in my case was that the vane was too light to overcome the weight of the heavy fleming major's counterweight. The result was that as the wind picked up to 5-7 knots or so the vane would move, and steer the boat fine, but as soon as the apparent wind dropped below this threshold the vane would come back near upright due to the heavy counterweight and a poorly balanced system. This made the steering very erratic in light shifty conditions with a rapidly changing apparent wind angle and strength.

When I added the weight to the vane I balanced it so as to only slowly return to upright with no wind, and the slightest breeze would deflect it. With this properly tuned rig the vane would steer the boat anytime she could sail and had basic steerage way. In very light airs at slow speeds the servo rudder didn't have the force to turn the main rudder, but it still kept the boat on course itself, provided the sails were helping with balance. It was a magical system once I properly tuned it. I used to go to sleep with the spinnaker up in light airs with no real worries about her keeping a decent course.

I wonder if the relatively heavy weight of the vane and it's counterweight acted as a damper, reducing rapid fluctuations in light airs due to the boat rolling?

[wingssail]

Originally Posted by Suijin

Lift would not be good on a wind vane.... You don’t want a wing “flying” in the airstream, you want a paddle that gauges and responds simply to wind direction.

I'm sorry Suijin, you are wrong about this. Snowpetrel (below) expressed it perfectly.

Some of the commenters were talking about how their vanes didn't work well in light air; the vane didn't produce enough force to twist the oar or move the rudder. Possibly an airfoil vane would be more powerful in light air but it is easier and simpler to just make it a little bit bigger.

Read snowpetrel's comment. He's got it right.

And, science is science, lift is lift, even when it comes from a flat airfoil.

[Snowpetrel]

Originally Posted by wingssail

We use a Monitor Light Air vane made out of some kind of very light weight plastic, possibly foam board, with tough plastic skins. (have attached a photo of it). It came with the used Monitor we bought in 1995. We also have two smaller, plywood, vanes which we intended to use in windier weather, but the plastic one has actually been through everything, and I mean everything, and now we never change it. We've sailed with the Monitor with this lightweight vane 99% of the time for over 55,000 miles, winds up to and including 50 knots, and sometimes it looks a little bendy, but its been fine. Due to its increased area it is very responsive even in light winds. We always put it away when not underway.

Interesting to hear it has survived through all the tough sailing you have done. The Vane I destroyed that was made out of that material folded in about 30 knots of wind, I wasn't very impressed! If it's handy I'd love some measurements, particularly it's thickness and if there is any internal reinforcing, such as tubes or rods through the middle of the webs.

[wingssail]

Originally Posted by Snowpetrel

Interesting to hear it has survived through all the tough sailing you have done. The Vane I destroyed that was made out of that material folded in about 30 knots of wind, I wasn't very impressed! If it's handy I'd love some measurements, particularly it's thickness and if there is any internal reinforcing, such as tubes or rods through the middle of the webs.

This vane is 118.75 cm (longest measurement) x 6.625 cm across.
The thickness is 6.35mm.

The construction is cored. The core is some sort of dense brown open cell foam, the skins are a woven material (I can see the weave where it prints through) approx. .3mm thick.

The finish is glossy and as smooth as glass (except for the mentioned print through of the skin weave) and quite hard, possibly epoxy.

As far as I can see there are no internal structural members.

Inspecting this vane carefully, which I have never done before, I see some damage to the tip where the skin is broken and some chipping at the base, probably from rough handling by the vessel's operator

There is no sign of cracking of checking so whoever made this (Scanmar, presumably) did a good job.

The paper monitor sticker is faded.

[Snowpetrel]

^^ Thanks for the very detailed description. I had assumed it was the twin wall polycarbonate stuff like most of the monitor vanes I have seen.

I have often thought using a foam core and epoxy with glassfibre, kevlar or even carbon skins would make for a very light and strong vane. Seems like yours proves the concept.

[model 10]

No it doesn't prove anything. I 've actually built a foam and fiberglass vane and it was no better than the stock Aries vane. As for my fab skills, I've built composite aircraft parts.
I don't think you could make an symetrical airfoil in that size anyway, 1/4" is just too thin to get any camber in the surfaces. Maybe some of the other vane gears have thicker airfoils than the Aries or Monitor and you might be able to build a pretty thick airfoil for them. It's pretty hard to get an airfoil to work at 4 knots and it takes a pretty thick airfoil section to do that.

[barnakiel]

Marine plywood plus two coats of epoxy will last a lifetime.


Ours is ss frame and canvas btw. I just give it new canvas now and then.



Cheers,

b.

[Jim Cate]

FWIW: The homebrew aux rudder/trim tab vane that I built for our previous boat had it's air vane made from two sheets of quite thin aluminium sheet separated by ~ 1 inch spacers... a design copied from the Auto Helm vane (now sold by Scanmar). There were outward turning spoilers on the trailing edge, and the dimensions were roughly two and a half feet tall by 6 inches wide t the widest part. The whole lot swung on a simple teflon bush bearing, and was balanced by a lead counterweight on athreaded rod that allowed adjustment of balance force. It was pretty big, and worked remarkably well in light airs. When the wind piped up one could pivot the blade downward, reducing its leverage on the counterweight, and that was sufficient to keep everything under control. It was heavier than the designs mentioned here, but managed to steer the boat for many thousands of miles, and without a failure. I did have one pintle failure, from poor welding practice and the rudder snapped off in a storm force knockdown. Only failures in over 85,000 miles.

The very similar Auto Helm system can be seen on Scanmars ads.

Jim

[philiosophy]

I bought some of that material they use for Real Estate signs. Needed a larger Wind Blade for my old Airies in lighter wind and to catch more air flow because I have a Wind Generater pole mounted straight ahead of the Aries. Gave that a layer of light weight fibre glass cloth and several coats of Marine enamel paint. It weighed the same as a standard wood blade. It works great in 25kts down to 6kts. Should last for many years. I also put a little teak oil on my wood air blades every few years. All good