windvane orientation...

[Butler]

This spring I will be able to do a rudder modification on my full keel Dreadnought that includes the installation of a trim-tab and subsequently that of a wind vane system. I may make my own or purchase the auto helm vane by itself from Scanmar for use with the trim tab.
Here is the question... I know that the vane does function, though not as effectively, in the horizontal position but I do not know if that means I can avoid having to switch to a split of double back stay by setting it up in the horizontal and pointing forward.
Vane gurus what say ye?
Thanks!

[gjordan]

It wont work at all in the horizontal position. Call scanmar and see what they say about hooking it to your trim tab.___Grant.

[Butler]

Thanks Grant, got it... I figured that the reason I'd spend the 2,000 plus to go with Scanmar over much cheaper DIY is for the support in setting it up, though before committing I would definitely need to see just how that unit would work with an owner installed trim tab. Seems like it would be a whole other kind of arrangement then what is used with the supplied rudder.
Appreciate the input horizontal v vertical. I may be mistaken but I thought that the Scanmar lit said it could be used horizontaly. Another reason I thought this possible was because of Moitessiers' experience with a horizontal vane (pp: 239 & 240, Cape Horn: The Logical Route) that he used on Joshua where he writes that while not as efficient as other gear available at the time it worked well enough. With Joshua the horizontal orientation was laid out aft though (illustration pig. 240)... it's not that splitting the back-stay would be a very big deal. Just thought maybe I could avoid having to do so. By the illustration the whole thing looks so simple.

[gjordan]

I may have misunderstood your post. What I ment was you cant take a vane that is designed to be a horizontal axis, and lay it on its side, and expect it to work. A trim tab system will probably work fine, but used windvanes are coming down in price since people are putting their faith auto pilots. An Aries or Monitor would probably steer much better and save you the time of building a vane. Everything about boats is some kind of compromise. Best of luck to you!______Grant.

[Butler]

Thanks Grant!

[cal40john]

It sounds like you can put it horizontal to clear a boom to tack, not to use it in that position.

You do know that the Autohelm uses a cable drive so the windvane can be mounted off center away from the backstay? There's a picture next to the Versatile mounting section of an off center mount. My friend with an OI 41 mounted his off center as well.


From Scanmar: http://www.selfsteer.com/products/autohelm/index.php

Adjustable Airvane

The horizontal axis airvane is most powerful in the the vertical position. By pulling the airvane down towards the horizontal position, it can be easily reefed to control the power of the trimtab. When clearance for the mizzen boom is needed, the airvane can be pulled all the way down.


Versatile Installation

The auto-helm comes in two halves - the airvane (upper) unit and the rudder (lower) unit. The two units can be totally separated, with the only connection being a wire running through a friction free teflon tube. The rudder can be mounted at the ideal height and the airvane higher up, where it gets the best wind. It is possible to avoid interference of davits, radar mast and other obstructions. The auto-helm windvane’s customized attachment system makes installation easy on most boats. Installation plans for hundreds of cruising boats are on file. Send us as much information as possible about your boat. We will make an installation drawing and mounting recommendation at no charge or obligation.

[rdubuque]

I am building a new rudder and am including a trim tab system mimicking the Autohelm model by Scanmar. So far it seems to be going quite well.

One question. Does anyone here have the dimensions of the actual aluminum vane with the holes in it. It appears to be about 36" long- 12' across the top, and 5' across the bottom where it attaches to the mast. Want to get it as exact as possible. The ability to reef this vane seems to be a very useful feature.

[Jim Cate]

Originally Posted by rdubuque

I am building a new rudder and am including a trim tab system mimicking the Autohelm model by Scanmar. So far it seems to be going quite well.

One question. Does anyone here have the dimensions of the actual aluminum vane with the holes in it. It appears to be about 36" long- 12' across the top, and 5' across the bottom where it attaches to the mast. Want to get it as exact as possible. The ability to reef this vane seems to be a very useful feature.

G'Day RD,

Don't worry about the exact dimensions of the wind vane... not at all critical. The important thing is that you must be able to counter balance the weight of the vane so that it balances with it in the vertical position. This position is for use in light airs, and you don't want to desensitize it. As wind strengths increase, you tilt the vane more towards the horizontal. This both decreases the lever arm and increases the inbalance of the weights... both of which desensitize the system and make it more stable in the stronger winds. A bit of experimentation is required, but it works very well when you get the hang of things. Basically, if the boat is over responding to yaw, lower the vane a bit at a time until it maintains a steady heading.

All the above knowledge was gained on our previous boat where I built a aux rudder-trim tab system similar to the AutoHelm model sold now by Scanmar. Steered the boat (an ex IOR one-tonner) for around 50,000 miles.

Incidentally, it is important to minimize friction in both the bearings that support the wind vane itself and in the cable drives for the trim tab. Keeping the mass of the vane as low as possible helps to keep those bearing loads low, too. OUr vane would steer down to about 5 knots apparent wind on any point of sail, which is pretty good as those things go!

Good luck with it, mate!

Jim

[rdubuque]

Thanks very much Jim. Now that I think about it, the size should not be such a big deal. Another sailor Christian Lloyd built one as well and said the holes in the vane are about 2" in diameter. I got the basics from that.

Going to be interesting getting out on the water, and learning to use it. At first I won't know if any problem are part of the learning curve or design flaws. Fortunately I know how to balance the sail plan quite well without the vane.

Very excited to get it finished, out on the water. Thanks again for all the comments and suggestions here.