Some interest in Dr. Dave's windvane has been expressed by visitors to the Columbia list, so this page is being put together to provide more information to those people.Dr. Dave Parker's Pathfinder Wind Vane User's Experience
A collection of personal experiences and advice
free, and worth every penny.
Revision 2, 19 May 2014
The first place to start, it seems to me, is with a set of definitions of the various important parts of Dr. Dave's windvane. These definitions are mine alone, and probably will seldom agree with more formal industry-standard definitions. So be it.
Let's work our way from the top down. That seems logical.
1. At the top we have the Vane. That's the thing that moves when the wind blows on it.
2. The vane is connected to the rest of the device at the Wig Wag. As its name implies, the wig wag moves back and forth however the vane wants it to, as the wind blows on the vane.
3. The wig wag is attached by loose-fitting bearings to the Head.
4. The head sits atop the Tower, and is free to rotate horizontally about on top of the tower so that the vane can be 'feathered.' The head has a wing bolt installed so that the skipper can lock the head into place against the tower when the vane is feathered on his preferred angle on the wind.
5. The base of the tower is attached to the transom or stern somewhere, so that the base is clear of the boat astern. The tower is mounted so that it is perfectly (+- 2 degrees or so) vertical when the boat is at rest. The tower is hollow so that the Upper Transfer Rod (actually just 3/8" OD aluminum or stainless tubing) can move up and down freely.
6. The upper transfer rod is attached to the wig wag so that when the wig wag moves, it moves the rod up or down. At the bottom of the rod there is a Bell Crank, so that this up and down movement is translated into a left or right movement, perpendicular to the centerline of the boat and the surface of the water.
7. The bell crank is connected at its other end to the Lower Transfer Rod. The lower transfer rod (Also 3/8" OD aluminum or stainless tubing) connects the bell crank to a short lever on the Oar Axle.
8. The oar axle, contained within an axle housing we will henceforth call the Control Arm, is connected to the Oar, which is in the water, and turns it left or right. That turning causes the oar to rise due to hydraulic force from the passing water.
9. The rising oar rotates the Centerline Axle which passes through the Centerline Axle Housing located at the fore and aft centerline of the boat. This rotation moves the control arm.
10. The control arm is connected to Control Lines, which are run through blocks to the tiller or a 7.5" hub at the wheel. When the control arm moves, so does the tiller or wheel. That is what steers the boat. Install the control lines in such a way that they run as near to perpendicular to the centerline of the boat as possible. Perfection will obviously be impossible here, but do the best you can and it will probably be good enough.
Dr. Dave built his device out of aluminum, schedule 40 stainless plumbing pipe, PVC plumbing pipe rings for bushings, 3/8" aluminum tubing and various other bits of useful hardware. The tower is of 3" aluminum, the head of slightly larger aluminum tubing, and the axle housings / control arm of stainless pipe. This pipe has an ID that I estimate at 1.5".
Installation and Construction / Maintenance Tips
All servo-pendulum wind vane oar mechanisms are designed to be mounted centerline. However, most manufacturers will also tell you, should you ask, that their device can be mounted off-center to accommodate boarding ladders or other such nonessential stuff. Obviously doing so will mean less oar in the water when on a heel, so a longer oar will likely be needed. Personally, I'd move all that other stuff to elsewhere on the boat so as to optimize placement of the oar mechanism, but that's just me. Use your own judgement.
The vane tower does not have to be mounted centerline or anywhere else in order to get unfettered access to the apparent wind. It's only important that whatever wind it gets is not wildly vortexed or dramatically diminished by deck paraphernalia such as cockpit enclosures, etc. So a mounting location where it would get flow off the main / jib on one tack, and clear air on another is fine.
Use very low stretch control lines, the fewest blocks possible, and make sure the friction lock on your wheel is not cranked down. Do all you can to reduce system friction, and do not allow slack in the control lines. Keep them TIGHT.
When constructing your system, I recommend STRONGLY that you not attempt to build a teardrop-shaped oar. You'll spend a lot of time, energy, and too much money doing so. Instead, buy one from a manufacturer. Cape Horn makes a lovely and durable teak oar, and Sailomat will sell you aluminum ones. Pick one, buy it, and then fabricate your oar mount accordingly. However, that said, Dr. Dave's mount was for a 1x4x48 bit of Hemlock lumber. Just a board. And it worked. It was noisy, it rattled and shook, but it worked. Contact me if you just MUST build your own oar. There are tricks to it. I spent far more time on the oars than on all the rest of the system combined. Don't make that mistake. Buy one. Or two. Design the oar mount to allow the oar to trail at an angle of about ten degrees, according to Dr. Dave.
There are two bushings inside both the oar axle housing (control arm) and the centerline axle housing. There is one bushing near each end of the housings. These bushings are 3/4" rings of PVC plumbing pipe. I found that chopping out about a quarter of each ring reduced friction, and a small shot of track lube reduced friction even more. However, neither change was actually necessary, as the system worked without those refinements. A nice touch here is that stocking spare rings is pretty simple, so replacing them every 12,000 miles or so won't be a challenge.
The system, as delivered, had several different sized clevis arrangements. I modified these so that all were identical. That made stocking spares simpler.
I modified the vane so that I could re-size it easily. I used a wing nut arrangement to make changing vane sizes quick and simple.
It is important to correctly balance the vane and counterweight assembly. Here's how:
1. Remove the head from the tower and lay it on its side.
2. Install your vane on the wig wag so that its flat surfaces are parallel to the floor.
3. Add small weights to the vane until it just balances against the counterweight. If the vane is heavier than the counterweight, reduce its size or increase the lever arm effect (or weight) of the counterweight.
4. Remove a small weight or two so that the counterweight drops reliably but not heavily every time.
5. Make the remaining weights fast to the vane where they are. It would be a good modification if you can make the counterweight adjustable somehow, so that it could be moved closer to or further away (to make the lever arm effect adjustable) from the wig wag.
6. Re-install the head onto the tower, complete with the vane. Connect the upper transfer rod to the wig wag, but disconnect it from the bell crank.
7. In calm conditions, with the upper transfer rod hanging freely from the wig wag and with the vane attached, the vane should be vertical but easily deflected from vertical by light wind. If it is not, adjust either the counterweight or vane accordingly and then reconnect the upper transfer rod to the bell crank. THE UPPER TRANSFER ROD SHOULD BE EXACTLY LONG ENOUGH TO CONNECT THE WIG WAG AND BELL CRANK WITHOUT MOVING THE VANE OFF VERTICAL. Installing a turnbuckle sort of adjustment device at the top of the upper transfer rod will make this simpler to achieve.
When designing your oar mount, make provisions for easily getting it out of the water while under way. My method was to use a dowel shear pin that was several inches longer than needed so that I could grasp it and pull it out, which made it easy to lift the oar clear with the line I kept attached to it for just that purpose.
There is another refinement that will make your system more responsive and reliable: first, make sure your oar is not bouyant enough to float by itself. It should sink reluctantly but reliably. Next, with the oar installed and with the control lines disconnected from the control arm and the lower transfer rod disconnected from the short lever on the oar axle, move the control arm until it and the oar are parallel to the surface of the water. Let go. The oar should drop to the surface and gradually (in two or three seconds or so) go on down to a vertical position, but not heavily. The oar should naturally seek to be vertical, in other words, which means the total lever arm moment below the centerline axle (when the oar is submerged) must be VERY SLIGHTLY greater than the total lever arm moment above it. If this doesn't happen, you'll have to add weight below the centerline axle. A good place to do so is near the tip of the oar (very little stress there,) perhaps built into the tip so that it does not disrupt the flow of water.
That's it. The pictures and the above will give you a good start to building your own Dr. Dave special. So here are links to all those pictures:
1, 2, 3, 4, 5, 6, 7, 8, 9
Hope this helps. Good luck.