Wind vane self steering design

Discussion in 'Boat Design' started by BillyDoc, Dec 13, 2005.

  1. BillyDoc
    Joined: May 2005
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    BillyDoc Senior Member

    Gentlemen,

    Being a dedicated lazy sort, I like to sail with wind vane self-steering. But I have not been happy with the available systems for many reasons and have always built my own. So far I have never been entirely happy with the result, although I think I have done better than a lot of commercial systems. Anyway, due to a recent severe case of cerebral flatulence, I am going to try it again and I would like your comments on my proposed system, presented below.

    First let me mention a few things I don’t like about existing systems.

    1. I don’t like any system that relies on electricity in any form whatsoever. Not that I have any thing against flowing electrons (I sometimes design circuitry for a living) but using electricity in a salty environment leaves entirely too many ways for things to fail. Besides, there are better ways.

    2. Wind vane self-steering systems must be as frictionless as possible between the sensing vane and the actuating servo rudder. If it isn’t, then you can forget about sailing down wind with one. This means good rolling bearings of some sort . . . and these are usually susceptible to corrosion, thus a build up of friction and eventual failure. Friction is bad, and so is corrosion. BUT, non-corroding bearings that can stand up to sea water either do not perform well (plastic bearings) or are so expensive you have to sell too many body parts to pay for them to actually be able to sail (ceramic with ceramic races). If a “sealed” bearing is used, my experience has been that the seals or the outer races corrode (even with “stainless”, and the seals themselves add considerable friction.

    3. Complex systems that are difficult to actually use or adjust interfere with my sailing. Did I mention that I’m lazy?

    So I have dreamed up the following system, in which all the mechanical parts between the sensing wind vane and the actuating servo rudder are immersed in a light oil which is pressurized slightly with an elevated and vented oil reservoir. There remain only two oil seals in the mechanical path from wind vane to actuating rudder. All the bearings in between can be high quality steel “open frame” types, which have very low friction. Additional oil seals will be placed as needed in areas that are actuated by hand or by the action of the servo rudder. A little extra friction doesn’t matter much in these areas.

    Please look now at the first figure, the wind vane head. This “head” is designed to be mounted on a post or the like on the stern, but could conceivably be mounted anywhere a good unobstructed wind direction signal can be found. Assume for now a vertical stern mount and that the angle of the wind vane relative to the boat has been fixed. We will get back to the business of changing that angle below. Assume further that the wind is coming from forward, which would be to the right in the figure, and that the boat has wandered off course to port.

    So, a boat rotation to port would cause the wind to exert a pressure on the starboard side of the sensing vane, which would be attached to the wind vane mount shown. This wind pressure would cause the vane to rotate to port, and this rotation would be translated through the wind vane shaft (with suitable bearings and an oil seal), through a “Helicoil” linkage, to the green “differential” gear at the top of the head. This green gear would then rotate clockwise as you look vertically down on the head. The lower, light blue, differential gear can be regarded as fixed for now. Three pinion gears are affixed to a yoke (red) between the green and light blue differential gears with open-frame bearings within each pinion gear. So, there is a two to one mechanical advantage between the green differential gear and the red pinion yoke which will likewise be driven in the clockwise direction, looking down. This red pinion yoke is mechanically linked to the “signal shaft” which exits the bottom of the wind vane head through suitable bearings. No oil seals are needed here, as this part of the whole apparatus will be immersed in lightly pressurized oil.

    Moving on to the second figure, we have a clockwise rotation on the signal shaft, looking downward, and this torsional signal represents an error from the boat drifting to port. We can use quite a few torsion shafts and bearings here, if we need to as there is little friction, and the “Helicoil” coupler is also very friction-free.

    In the second figure the right side would be forward, and the servo rudder is mounted in an enclosed structure that can pivot about a horizontal axis. Suitable bearings and oil seals would be included, naturally, but are not shown here for clarity. The shaft connecting the green gear to the servo rudder would pass through this structure with (again) suitable bearings and the second oil seal in the wind vane to servo rudder mechanical path.

    A clockwise rotation of the signal shaft, looking downward, results in a clockwise rotation of the grey gear, looking forward (to the right). This clockwise rotation of the grey gear will drive the green gear counter-clockwise, looking downward, thus causing the servo rudder to likewise rotate counter-clockwise, to port.

    Assuming a flow of water past the servo rudder from right to left in the figure, the counter-clockwise rotation of the servo rudder will cause a force to be exerted against the starboard side of the servo rudder, thus causing it to pivot about the horizontal axis comprised of the grey gear and it’s drive shaft, and the enclosed structure, in a clockwise direction as viewed from aft. This rotation of the enclosed structure will result in two things: first, an attached rudder actuator can be used to drive the rudder appropriately, and second, since the grey gear is stationary (relatively speaking) the green gear rotating about it will tend to rotate the servo pendulum back to its original orientation relative to the flow of water. This gives us a proportional correction which is very important to a self steering system because it means that the force exerted can exactly match the steering requirement without a lot of hunting and overshooting. The direction of the servo rudder’s deflection is such that the servo rudder itself exerts a steering moment on the boat which is in the same direction (correcting to starboard) as the rudder it drives, so there is no energy lost by having both surfaces “fighting” each other.

    Now about that mess of differential gears in the wind vane head.

    As should be apparent, there are some real advantages to a torsional error signal, and this would be easy to implement if we always sailed on a fixed course relative to the wind. This might prove inconvenient, however, so if we are set on using a torsional error signal we must have some way to “decouple” the error signal when we rotate the wind vane head to a new relative course, and then re-couple it. Some sort of clutch could be used, but . . . did I mention that I’m lazy?

    Looking back at the first figure, the wind vane head, imagine that the whole head is mounted in bearings with an oil seal and a worm-gear drive arranged so that it can be rotated about its vertical axis from wherever I want to mount my crank. Like in a center cockpit, for example.

    If I rotate the entire head (and the wind vane is assumed to be fixed relative to the head, for now) then the green gear will rotate with the head and try to drive the pinion gears and the red yoke with it. On the other hand, if the light blue gear is rotated by the same amount in the opposite direction, the two rotations will cancel each other out at the pinion gears, and the red yoke will remain stationary, relative to the boat. This second rotation (of the light blue gear) is accomplished by affixing the purple yoke to the hull through the shaft shown in the figure. The grey gear, affixed to the head, will therefore drive the pinion gears associated with the purple yoke, thus rotating the light blue gear in the appropriate direction . . . in exact proportion to the original displacement but in the opposite direction, as required. The light blue gear just floats between the two sets of pinion gears and is attached to nothing.

    The intent of this design is to build the whole thing into the hull as an integral part of the boat. I never go far from land without self steering, so . . . why not? Having a lot of it below decks also offers some protection, and it would be simple to plumb in that oil reservoir somewhere convenient and protected, like in a pilot house. Oh, the little red thing at the top right of the wind vane head is a bleed port so the air can be vented and the entire inside flooded with light oil. This means that the oil reservoir has to be higher than the bleed vent, obviously. The oil provides some damping as well as protection from salt water.

    The design of the oil seal on the servo rudder is a little tricky, as this will not only be under water at least part of the time but must be able to withstand surges from pounding against the water’s surface. I have been thinking of incorporating a narrow gap between the servo rudder shaft and a larger volume chamber surrounding the shaft, with a baffle on the shaft to prevent a direct impact from the water against the seal. In this way a momentary surge from pounding would have to fill the chamber before it pressed very hard on the seal. This chamber should also be vented to atmosphere somewhere to facilitate draining.

    So, there you have it. I hope you will work through the logic of the thing, and if you find any errors PLEASE let me know! I have more than a little difficulty wrapping my brain around this thing and can use all the help I can get. If something is not clear, just ask!

    BillyDoc

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  2. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    Only question for me is how easil the penlum can be moved by the stern moving down the side of a wave.
    On the Aires system the best part is how well the unit handles large following seas, The stern gets kicked a bit and the servo is instantly giving the helm the proper direction to get back on course.
    No wait for the air flow to catch up.

    Will your unit do that?

    FAST FRED
     
  3. BillyDoc
    Joined: May 2005
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    BillyDoc Senior Member

    Hi Fred,

    I believe so. The Aries and the design above are set up so that the pendulum servo rudder exerts a force on the water in the same direction that the rudder itself does when activated. So, when sliding a bit sideways down a wave and exerting a force on the servo rudder directly (either the Aries or mine) the resultant correction is the same.

    If I did this right (and there may be some doubt there) you should be able to "box up" both units so you couldn't see the internal workings and the action on the servo rudder resulting from a force on the wind vane would not be distinguishable between them . . . except for friction. The reason I have taken the approach I have is twofold: to reduce system friction (thus improving performance), and to protect the components from corrosion or direct damage. The Aries looks like a fine machine to me, actually, and I studied it carefully at one time. I couldn't afford it, though, so I built my own.

    On another topic, I want to apologize to everyone for the pictures above, I couldn't get the "thumbnail" thing to work. They are in a .png format, too.

    Bill
     
  4. gonzo
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    gonzo Senior Member

    The main problem I see, is that if the coils are soft enough to create little friction or torsional force, they will also provide a sloppy movement. How do deal with that?
     
  5. BillyDoc
    Joined: May 2005
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    BillyDoc Senior Member

    Good point Gonzo,

    The thing could be made as drawn, with a couple of interleaved springs, but that would give a "soft" response in torque as you point out, and I want the linkage to be stiff in torque but still accommodate the required angular displacements.

    When I first started thinking about this design I got on the web and googled on "flexible couplers" or some such, and came up with a longish coupler that looked like a stainless steel rod that had a bunch of interleaved slits cut in the side so it was flexible in a radial direction but stiff torsionally. I believe the thing would accommodate something like 30 degrees. It looked perfect for what I had in mind. Naturally, I can't seem to find it again. I thought the brand name was "Heli-coil" but apparently I am mistaken, their web page only seems to have thread inserts. I'll keep looking.

    Any coupler is going to exert some force on the bearings holding them in place, but good hardened steel bearings do not change their rolling friction very much with the application of the small radial loads we are talking about here. Ceramic is even better, of course, but there is that cost thing.

    And then there are always bevel gears, which may actually be best in this application.

    The problem is, assuming the wind vane is tilted about 18 degrees from the horizontal (which will give it a proportionating behavior), then that leaves 72 degrees that the torque needs to be turned initially, then another 90 degrees or so below the vane head to drive the servo rudder. This is a lot of torque redirection, and the simplest way to do it with the least friction is not obvious to me. Should I use the helical couplers? Bellows type couplers? Universal joints? Any ideas along these lines will be greatly appreciated!

    Bill
     
  6. BillyDoc
    Joined: May 2005
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    BillyDoc Senior Member

    Found it!

    The coupler I originally found is here: http://www.heli-cal.com/Html/Products/ujoints.htm

    Heli-cal, heli-coil . . . computers are so picky!

    Anyway, Heli-CAL claims an angular displacement capability up to 90 degrees and:

    No Backlash
    No Moving parts
    No Maintenance and lubrication requirements

    So, two or three of them in the system. I would think, since there is no sliding or even rolling friction involved except for a few bearings, that they would be relatively friction free in the application shown above. Also, since each helical "beam" is thick radially, torque transmission should be fairly good. It shouldn't take much anyway, if the system is well balanced to start with.

    Bill
     
  7. gonzo
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    gonzo Senior Member

    They claim torque capability of up to 150 ft/lb. That should be enough for a vane steering.
     
  8. BillyDoc
    Joined: May 2005
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    BillyDoc Senior Member

    Absolutely.

    A detail not shown above is a friction connecting surface with a single pivotable bolt through it attaching the servo rudder to it's shaft. This serves two functions, if you hit something the joint will simply slip and alow the servo rudder to fold up, and you can use this joint to adjust the balance of the servo rudder. I plan to adjust the balance by getting underway with a friend and pivoting the servo rudder forward or aft at this joint until I can easily steer the boat back and forth by twisting (in this case) the signal shaft with my fingers . . . but a little less than neutral so it will return to center when I release the signal shaft. This capability means that the foil shape doesn't have to be perfect, although that would be nice, and simplifies the design.

    And of course we do sometimes hit things at sea. I once split a partially submerged wooden crate completely into two parts with a Contessa 26. Tough boats, those Contessa's.

    Bill
     
  9. OldYachtie
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    OldYachtie Junior Member

  10. BillyDoc
    Joined: May 2005
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    BillyDoc Senior Member

    Lost the images . . .

    The images for my original post needed to be loaded from a web site that no longer exists (because I couldn't figure out how to load them here) and the post is so old I can't edit it . . . so here they are!
     

    Attached Files:

  11. lazeyjack

    lazeyjack Guest

    why do you need to move the nain rudder, would it not be best lock the main rudder, and use a secondary rudder long span small chord, or even a trim tab on that secondary rudder, you are surely making a chore trying shift the main rudder
    I should intro you to my mate also PHd , who sailed Kate around the hORN from NZ to Uk
    betcha you will be 90 and still designing beautiful objects for THAT boat:))
     
  12. BillyDoc
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    BillyDoc Senior Member

    Damn, I hope so!

    To answer your question, LazeyJack, a trim tab on the main rudder also works but the linkage to operate it is more complex and much more exposed to corrosion. Just locking the main rudder would also work, but not as efficiently as having the main rudder AND the servo rudder acting in the same direction, which this design attempts to do. Another advantage is that I intend to use hydraulics for the steering linkage, which means it is simple to switch (valve) the self-steering into and out of the steering loop when needed.

    And to respond to the other question properly, the wife has given me three and a half years to get this baby in the water . . . or else! She hasn't told me what "or else" means though. She retires in three and a half so she probably plans on working on it then.

    BillyDoc
     
  13. BillyDoc
    Joined: May 2005
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    BillyDoc Senior Member

    Very good points Alan. Let me get this description in here before proceeding. I am quite excited by the ideas you have presented! And don't worry about corrosion, I plan to immerse the whole mechanism in oil. That way I can use open-frame bearings and I only have to deal with a very few oil seals.

    The basic function.

    The whole point of wind-vane self-steering gear is to steer the boat relative to the wind, so let's start there. Look at Figure one first (in post #10), and imagine an airfoil section mounted vertically on the blue wind vane mount at the top of the figure. The wind would be blowing from right to left across this wind vane, and as long as the vane is perfectly aligned with this wind it will remain vertical. No error signal is generated in this case (we'll get to the “error signal” below) and the boat will stay happily on course because we previously rotated the whole structure shown in Figure one on it's vertical axis to align the wind vane with the wind while at the same time maintaining the desired course by hand.

    But alas, things never remain static and we are bound to eventually drift off course relative to our wind unless we make corrections. Assume we drift a bit to the left of our desired course (counter-clockwise, looking down on the boat). Now the wind is no longer aligned head-on with the wind-vane, but is applying pressure on the side nearest us. The wind-vane mount is pivoted on the wind-vane shaft, which is mostly horizontal, so the wind-vane will be pushed away and cause the wind-vane shaft to also rotate. Note that I said “mostly” horizontal. Actually the wind-vane shaft is inclined 18 degrees from true horizontal, and this gives the wind-vane an important property: it's angle relative to the wind changes as it is rotated in such a way to again bring it into alignment with the wind. In other words, the magnitude of the rotation of the wind-vane is proportional to the magnitude of the wind direction error. This is a very desirable property to have in a wind-vane and is often implemented (look at an Aries, for example).

    The wind-vane is also counterbalanced with the purple weight to a point where in a still room it will just barely remain upright.

    The gears shown in Figure one serve one primary purpose only: they allow the entire wind-vane “head” to be rotated on it's vertical axis to set a course relative to the wind. But before delving into that particular mind-twister, let's just assume a fixed relationship on the course setting and skip all the gears for now. To do that, just picture the torque from the wind-vane shaft being transmitted through the green spring-looking heli-cal device straight through the mess of gears directly to the red “Signal shaft.”

    Now look at Figure two. The red “Signal shaft” passes torque through a second heli-cal device to a gray bevel gear which is driving a green bevel gear which is rigidly attached to the shaft of a servo rudder through suitable bearings and seals. The gray bevel gear is free to rotate within a bearing mounted in the blue structure, and the blue structure is free to rotate on an axis coincident with the gray bevel gear. In Figure two the right side of the figure points to the bow of the boat, so water will be flowing from right to left across the servo rudder. As long as the servo rudder is oriented directly into the water flow, it will remain vertical. If the red signal shaft rotates, however, thus rotating the gray bevel gear and subsequently the green bevel gear and servo rudder, the servo rudder will pivot either toward or away from the observer looking at the Figure. In the example above we had a course error to the left relative to the wind which caused the wind-vane to pivot away from the observer, which will cause the green bevel gear to rotate clockwise-looking-down, which will cause the red signal shaft to also rotate clockwise-looking-down, which will cause the gray bevel gear of Figure two to rotate clockwise-looking-forward, which will cause the green bevel gear of Figure two to rotate counter-clockwise-looking down, which will also cause the servo rudder to rotate counter-clockwise-looking down, which will cause the servo rudder to rotate clockwise-looking-forward on it's horizontal pivot . . . thus steering the boat to the right and applying power to the rudder actuator to steer the boat to the right thus correcting the original error. (Phew!) Note that as the servo rudder pivots on it's horizontal axis it also rotates the green bevel gear relative to the gray driving bevel gear (Figure two) in such a way to cancel the original error rotation. This cancellation effect as the servo rudder rotates on it's horizontal axis produces a proportional response at the servo rudder that is also highly desirable.

    Course setting.

    A simple way to set the desired course could be to put some sort of clutch in the signal shaft and simply decouple this clutch to rotate the wind-vane on a vertical axis. But I tend to get rather lazy when at sea, what with the sea-sickness and all, and I just don't want to be climbing aft and trying to set the wind-vane, then back to the center-cockpit to adjust the course with the wheel, then back aft to try again . . . and so forth. So, I was looking for a way to keep the arrangement described above but be able to just arbitrarily adjust the course using a worm gear on the entire wind-vane head assembly. I envision a small crank in the cockpit for this, with a long torque tube to a worm drive on the self-steerer. I did something similar on another boat I had and it was most convenient!

    It should be obvious, however, that simply rotating the wind-vane head will really screw up the relationship between the wind-vane and the signal shaft if something isn't done about it. What we need here is a way to be able to rotate that head but at the same time cancel out the effect of that head rotation on the signal shaft. Which is the whole point of the mess of gears shown in Figure one. Here's how it works.

    First let me explain what you are looking at in Figure one. There are two “differential” gear sets, the top one comprised of a green bevel and a teal bevel, with a red three-way yoke in between that has three gray bevel gears attached by bearings. The red yoke is directly attached to the signal shaft, so when the green bevel rotates, say, 180 degrees, and the teal bevel is stationary, then the signal shaft will rotate exactly half that distance, or 90 degrees, in the same direction. All the functioning of the self-steering apparatus is the same as described above, except that the magnitude of the rotation on the signal shaft is half what it was.

    We want to preserve the relationship between the wind-vane and the servo rudder and also be able to rotate the wind-vane head on a vertical axis. This means that we have to cancel out the effect of the rotation of the wind-vane in some manner. We do this with the second “differential” gear set comprised of the teal bevel gear and the gray bevel gear with the purple three-way yoke in between that has three gray bevel gears attached by bearings. The teal “double bevel gear” is not attached to anything except the six small gray yoke bevel gears. The purple yoke is fixed relative to the hull of the boat, and the bottom gray bevel gear is fixed relative to the wind-vane head.

    Now when we rotate the wind-vane head on it's vertical axis, the gray bevel gear drives the three gray bevel gears on the purple yoke (fixed to the boat) thus driving the teal double-bevel gear by the same number of degrees in the opposite direction! The green bevel gear is also effectively attached to the wind-vane head and it also drives the gears of it's red yoke, thus driving the “teal double bevel gear” in the opposite direction by the same number of degrees exactly as the lower differential gear set has done. Thus the two yokes stay stationary in their positions if the wind-vane and servo rudder remain stationary relative to their respective attachments, yet the wind-vane head is rotated as desired and the function described above for the wind-vane to effect steering has not changed at all.

    I apologize for the length of this post, but I have a good excuse: just figuring out the above relationships completely broke an otherwise good brain!

    BillyDoc
     
  14. lazeyjack

    lazeyjack Guest

    And to respond to the other question properly, the wife has given me three and a half years to get this baby in the water . . . or else! She hasn't told me what "or else" means though. She retires in three and a half so she probably plans on working on it then.

    BillyDoc[/QUOTE]
    well given there is abt 3500 hrs in the metalwork for a good man, and 2000 for the woodwork, and in your case a billion for gee jaws gismos, that three and a half years is looking a bit , um, then of course there the lectrics, plumbing, sewage electronics
    and if you a re going to fill fair and paint 1000 hrs , gee I,m getting tire thinking abt it mate
    but you can do, if you knuckle down buckle down as Rodger Miller sings
    yes its possible, its the fairing that the killer GOOD LUCK BON CHANCE!!
    Oh my first build in 78, I tried getting a link down the hollow rudder stock onto a trim tab,
    by half way thru, I,ll sail over in my simple chine boat and give you a hand, by then Maybe they will let me back into USA:)
     

  15. BillyDoc
    Joined: May 2005
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    Location: Pensacola, Florida

    BillyDoc Senior Member

    I'm sorry Alan, but I don't know what you mean by this. Are you talking about the wind-vane and the servo rudder? If so, are you asking how much "slop" is acceptable between the rotation of the wind-vane shaft and the rotation of the servo rudder shaft? As little as possible! Any "slop" will be a potential source of vibration, although I will balance the servo rudder so that it will be pivoting slightly ahead of it's center of lift and will add weight internally forward of that to prevent just this sort of "flutter."
     
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