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Old 13-06-2013, 05:20   #1
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Wind Vanes

I have a question relating to horizontal axis vanes. I have read some research that says the optimal angle of the air vane axle is 20 degrees off the horizontal, leading edge up. This imparts damping to the vane in that as the vane is deflected off the vertical during a course correction, the lee side gradually presents its face to the wind flow thereby smoothing out its motion. As far as I know, almost all self steering manufacturers of horizontal axis vane systems mount their vanes at or close to a 20 degree inclination.
I am wondering is this is more theoretical than practical because it would appear to make two assumptions - (1) that the wind flow is always horizontal and (2) that the boat sails upright, and neither of these is the case. The wind may be directionally stable but at wind vane level it dances around a bit, affected by the sea state, and boats don't sail upright. Given a 20 degree angle of heel then the wind vane axis is at 40 degrees - twice the recommended figure! If 20 degrees is the optimum vane angle, then isn't it better to build the vane axis level and allow the boat's sailing heel to provide the axle inclination?
My question might be just as theoretical, but it is easier to build a horizontal axis vane than an inclined one.
Would be really interested in all the collective wisdom.
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Old 19-06-2013, 12:37   #2
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Re: Wind vanes

The angle of attack of most aircraft wings peaks out at about 20deg also. You would think the airfoil shape would have a greater effect but it does not seem to unless you are talking super-duper airfoils. I think there is something involving fluid dynamics going on there and with air vane paddles also. Sails to I guess.
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Old 19-06-2013, 13:11   #3
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Re: Wind vanes

FWIW, it's my understanding that Nick Franklin, the builder and designer of the Aries vane built a test vane that was infinitely adjustable before he went into cast aluminum for the production version. He supposedly experimented with various pivot angles with this test mule vane and came to the final design angle through that testing. At least for Nick, who made the first widely available vane that worked that has been widely copied since, found the 20 degree angle to work best.
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Old 19-06-2013, 14:18   #4
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Re: Wind vanes

No mention of that on the manual for my original aries, other than tilting the vane back 45 deg to clear a mizzen shouldn't be a problem. Installation specifies the 2 top tubes to be horizontal
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Old 19-06-2013, 16:15   #5
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Re: Wind vanes

Quote:
Originally Posted by Chrisc View Post

(...)

it is easier to build a horizontal axis vane than an inclined one.

(...)
How is it easier? I do not see any challenge at all in building a vane with its axis at 20!

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Old 19-06-2013, 16:19   #6
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Re: Wind vanes

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The angle of attack of most aircraft wings peaks out at about 20deg also. (...)
This is different. The vanes are in fact often adjustable in this respect (Aries is, Windpilot is, Sindbad is).

The 20 degrees in not the "perfect" angle of attack, it is the angle that the axis of the vane makes with the horizontal.

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Old 19-06-2013, 17:28   #7
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Re: Wind vanes

The horizontally pivoted vane is extremely sensitive and powerful. A flat horizontal pivot point didn't work in practice because the windvane was so sensitive. It would slam from side to side with very small changes in wind direction grossly oversteering the boat. The solution was to angle the pivot point. What this does is decrease the angle of attack as the vane pivots down to be near 0 at 30 degrees of vane rotation. The vane becomes self dampening, quick to sense small changes in wind direction. but not over controlling.

Nick Franklin pared Blondie Haslers pendulum servo steering system with a horizontal vane, someone else's innovation, to control it making self steering practical for the common sailor. Hasler remained wedded to vertical pivoting vanes and never really caught on. The vertical vane lacks sensitivity to small changes in wind direction so weren't as effective at steering the boat.

This is a good site explaining the technical aspects of Self Steering and a little history.http://www.books-for-sail.com/boats-...-steering.html
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Old 19-06-2013, 20:03   #8
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Re: Wind Vanes

I accept that an inclined horizontal axis vane is necessary - I have messed about in my workshop with a test rig and an industrial sized fan and concur that an angle off horizontal provides a good damping effect to the vane. Whether 20 degrees is the optimum I cannot say as I don't have any test equipment to determine this, but accept that it is, based on the opinions and experimentation of people a lot smarter than me.
The issue is the boat's angle of heel, which on most points of sailing is going to provide somewhere around the desired 20 degrees of vane inclination. If we add the boat's angle of heel to the vane inclination then, under most circumstances the vane's axis inclination to the horizontal is actually around 40 degrees. Is this in fact what is actually required? Down wind of course is another story, and the way my boat rolls like an old lady with too much to drink would probably tend to nullify any of the above considerations.
Barnakiel, I am only a back yard engineer with nothing going for me other than my enthusiasm. On my test rig the vane shaft turns on two teflon bearings. When horizontal it is almost frictionless, when inclined 20 degrees the weight of the vane, counterweight and particularly the linkage imparts a slight increase in friction as the weight comes on the additional bearing surface between the shaft end and the rotational bearing, exacerbated if increased to 40 degrees. Also, I find linkage attachment to the shaft a little more complex at a 20 degree angle than when at right angles as with a horizontal shaft. I am trying to build a system as friction-free as I can. Certainly a good engineer could achieve this, but.....me?
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Old 20-06-2013, 00:46   #9
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Re: Wind Vanes

the 15-20 degree horizontal angle - you can theorise about it til the cows come home - when you see the vane in action it is very obvious how and why it works. Depending on the system you are building it may be the only form of damping in the system.
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Old 20-06-2013, 02:26   #10
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Re: Wind Vanes

From the test bed:
With the vane axis at the recommended 20 degrees, ie boat upright, airflow regulated at 12metres/sec (approx 23 knots) and an angle of attack at 7 degrees, I get a vane deflection of approx 33-35 degrees before damping becomes apparent. At the recommended 3 : 1 linkage this gives a trim tab correction of 12 degrees.

With the vane axis at 40 degrees, ie boat healing at 20 degrees with the same airflow and angle of attack, the vane deflection is 15 degrees before damping kicks in, giving a trim tab correction of 5 degrees. Less, when you need more.

Hmmm, maybe a vane head with counterweights so that it is always at the optimum 20 degrees, regardless of boats angle of heel..
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Old 20-06-2013, 17:47   #11
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Re: Wind Vanes

depending on how well your boat points you have a semicircle of up to +/- 270deg of vane angle. take out the 180 deg from reach to downwind, add to this that most boats will self steer close hauled - does your test bed take all this into account? the heel of the yacht has no negligible effect on the operation of the wind vane IN PRACTICE. Generally windvanes steer the boat in long s lines which average out to a pretty straight and efficient course. You're barking up the wrong tree, chris. It's not that complicated. The really interesting stuff around using windvane ss is in the use and balance of sails.
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Old 20-06-2013, 19:55   #12
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Re: Wind Vanes

Charliehows, Unfortunately I think you are correct and that I'm on a highway to nowhere with my research and my test beds etc.
In my defense, I have many thousands of happy miles with windvanes of my own construction, certainly enough to appreciate just what wonderful devices they are. My wife says that my constant tinkering has become an obsession, but I think that's a little harsh......
The question that drives me is, has the vindvane reached the pinnacle of its development? That's it? No room for further improvement?
Sometimes when I get on my bicycle with its T6 alloy frame, carbon forks, 21 speed Shimano cluster and balanced epipoise cranks I am reminded of John Kemp Starly (I think that was his name). In 1885 he produced the first equal wheeled chain driven steerable bicycle and declared "The velocipede has at last attained the summit of its capabilities."
On the extraordinarily remote off-chance that I have a 'Eureka' moment that produces something worthwhile, I'll share it.
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Old 20-06-2013, 21:37   #13
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Re: Wind Vanes

well, they have improved quite a lot - if you get a chance to see a new fleming for example, they have become light, compact and very sleek indeed - trouble is - they do cost a bit. I know my own hand-made unit has a few compromises i'd rather not have made but it works and it cost f-all so i live with it. The main thing i think that falls down on hand made units is that people underestimate the strength of construction required for dealing with the full range of sea conditions the unit is going to be subjected to. But, like you, i have spent many satisfying hours tinkering.
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Old 20-06-2013, 23:26   #14
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Re: Wind Vanes

We bought our first vane in Jan. 1970. We used it till 2004 when we sold our boat. Now this was not without repairs! But the same set up and basic parts !! Had an early Iron Mike, which used huge amounts of power so you can see we used the vane all the time on all points of sail All I can say is our new to us boat is without one, at least this week it is LOL Soon tho she will have a new Vane system. I believe in them ! and so do Connie. Just our two cents
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Old 21-06-2013, 06:20   #15
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Re: Wind Vanes

Bill Belcher for his wind-vane book made all manner of test rigs and interestingly he couldnt see benefit to having the axis at any angle other than 0 degrees. Only makes for a more troublesome linkage.
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