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Thread: Air rudder for a big rowboat?

  1. #36
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    Default Re: Air rudder for a big rowboat?

    It worked very well. Smaller and lower was less effect than the first try, but it still balanced the boat well going upwind and tended to head up instead of bear off in the gusts. It was much less effort to stay pointed into the wind, I could just row steadily and not need to suddenly yank hard to one side.

    Releasing the oars and drifting she still turned beam to the wind and waves. With no board down there is no resistance to the turn, and the boat does not track straight going backwards due to the skeg.

    Rowing beam to the wind was fine with the air rudder over. I was probably imagining it, but it felt like a little boost from the wing.

    Now rowing straight downwind was tricky. No angle worked well, I had to tack downwind.

    The final configuration needs some way to easily stow the wing, or maybe allow it to rotate freely. A round shaft with a locking pin?

  2. #37
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    Default Re: Air rudder for a big rowboat?

    Aaand, just a picture of the TSCA fleet docked at Benicia, ready to depart on a week long Delta cruise tomorrow:


  3. #38
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    Default Re: Air rudder for a big rowboat?

    Sigh...

    Peace,
    Not There

  4. #39
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    Default Re: Air rudder for a big rowboat?

    I'm really interested in this experiment as I have a 15 foot Tammie Norrie which I row quite a bit, I am normally alone so have to shift to the forward position to row to windward so I keep the bow further into the water (even with 20 kilograms of water ballast in the bow) and I still have problems staying on course.

    There's a lot of free board and it's a light boat. I've used the centreboard which helps but it's better with CB and rudder deployed although that increases drag and requires steering while trying to row.

    On one occasion I was hit with a sustained gust on the port bow and was nearly pushed onto rocks, even rowing flat out on stbd only wasn't helping. I had to go forward on stbd and astern on port to turn her into the wind and just made it.

  5. #40
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    Default Re: Air rudder for a big rowboat?

    You should try a round post and a grip-like locking mechanism, allowwing to steady your course at any wind angle. And keep it free spinning on downwind tacks...

    My 2 cts...

  6. #41
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    Default Re: Air rudder for a big rowboat?

    Rob - Me too! I'm at work now, they are sailing to Pittsburg.

    Steve - Been there with the boat pushed by a gust, did not like it. I used to think I had to pull away from the rocks, like you I now realize it's best to turn quickly then pull on both oars. This wing of Clarkey's has promise, I still need to test in some really strong (30+) conditions to make sure it doesn't go unstable, but so far so good. You have a CB also which should allow parking. I would say try something simple, just a fixed board, to see how the Tammie Norrie behaves.

    L'Ankou - Ability to point the wing to any angle and lock it sounds good, but I don't see an easy way to make it work. If it had a pin on a round post, and the pin had a lanyard, I could pull the pin from the cockpit to decouple it fast if needed, then go back to put the pin in again when things calm down.

  7. #42
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    Default Re: Air rudder for a big rowboat?

    Rick - Thursday may provide the wind you're asking for! I'm joining the gunkholing crew for Tuesday and Wednesday, but will be motoring back to Sugar Barge Marina in all that windy stuff on Thursday. r
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  8. #43
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    Default Re: Air rudder for a big rowboat?

    For a locking mechanism, consider the bicycle seat post lever/cam lock.
    -Dave

  9. #44
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    Default Re: Air rudder for a big rowboat?

    with a small pull rope to release the cam...

  10. #45
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    Default Re: Air rudder for a big rowboat?

    Say there is a socket part attached to the steering yoke. This needs to turn maybe 120 degrees stop to stop and is controlled by the steering line. The wing is attached to a shaft that slides into the socket, easy to pull when not used. Most of the time the wing should be aligned so it is straight aft when the helm is amidships. The rest of the time it should swing freely. I can do that with a pin, maybe a spring pin that pulls loose with the lanyard and springs back when the lanyard is released.

    Edit - this kind of pin:


    I am not sure how the seatpost cam lock would be better. How does it register to the aligned position, and how do I actuate it both clamping and releasing? Maybe this works, I'm just not getting it.
    Last edited by rgthom; 06-03-2019 at 05:33 PM.

  11. #46
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    Default Re: Air rudder for a big rowboat?

    My thought is that it can be locked at any angle. And there's no need to line up holes to slide a pin in, something that I usually find frustrating.
    -Dave

  12. #47
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    Default Re: Air rudder for a big rowboat?

    It's easy to say put a locking pin in or whatever but in practice a small boat like this with a crew of one becomes unruly the moment you stop rowing in anything other than perfect conditions. To have to go aft, stand up and fiddle with a pin while your long narrow boat is being turned across the wind and waves is far from ideal.

    To that end I like everything to be managed from the rowing position. I would enlist the help of the tabernacle and leverage.

    See two possible examples below. They both require the air rudder to be amidships to activate but will lower the rudder to the deck easily and at that point if still necessary the rudder can be disengaged from its mast and turned easily and safely.

    Example 1

    A scissor brace forward of the mast pivoting at both attachment points to the mast and the fulcrum, a halyard from the fulcrum back through a sheave in the lower mast and forward to a cleat will raise the mast and lock it in that position while a down haul coming forward from the fulcrum will lower the mast while the operator keeps tension on the halyard to ease the motion. (EDIT) This may not work so well as the halyard will interfere with the lower scissor brace leg to some extent when turning the rudder.

    Example 2

    A single fixed stand off brace aft of the top mast with the halyard attached to the top mast and the brace before passing through a sheave in the lower mast to a cleat on deck. The down haul will be the same as above. In this case some experimenting would be required to get the angle of the top mast brace correct so it is easy to raise the mast with the halyard from stowed position although I think both systems would always need a push up to start them raising.

    In either case the halyard sheave is very close to the centre of rudder rotation so the tension on the halyard won't impede rudder function.
    DSCF1460.jpgDSCF1459.jpg
    Last edited by Steve TN 15; 06-03-2019 at 10:53 PM. Reason: Found a possible flaw in my diabolical plans for rudder domination

  13. #48
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    Default Re: Air rudder for a big rowboat?

    I see it may become quite complicated...

    taking a round mast/post, cylindrical.

    assemble the rudder blade on a PVC pipe (example) with an internal diameter just above the mast OD. Name it rudder base.
    The lower part of this PVC rudder base will be notched
    The top part plugged to retain the blade on board, with a screw / nut / whatever from the top to keep it down on the mast.

    On the mast, below the PVC, will be another piece of PVC pipe, with the upper half enlarged (heat gun) to slip around the rudder base, thus locking it to the mast.

    A small rope to pull it down will release the blade, leaving it free spinning,

    A jamming motion by hand will lock it in place...


    IMG_20190604_105250.jpg


    Now I leave you for a while, my old 2-wheeled BMW is calling for a ride around Marseilles

  14. #49
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    Default Re: Air rudder for a big rowboat?

    Wow, you guys are really going to town on this.

    I'm still concerned it may not work in the high winds where I need it most, so waiting to do some more testing of the current rough prototype. I would try something quick and dirty on any other boat also, it may not behave the same as Walkabout which is really a sailing hull.

    If it does work well, then we need to decide what NACA profile to use. I would shoot for airspeed about 30 kts, much more than that I cannot row far anyway. It should have a high stall angle, so righting action is by lift and not just drag which pulls the boat backward.

    Steve - I *think* that a spring locking pin could be made to work from cockpit controls. Just a line to the pin, pull and cleat it to release the wing. To latch the wing, uncleat the line to release the pin and turn the boat by oars until the pin engages the alignment hole.

    Rick

  15. #50
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    Quote Originally Posted by L'Ankou View Post
    I see it may become quite complicated


    Now I leave you for a while, my old 2-wheeled BMW is calling for a ride around Marseilles

    Now that sounds fun...


    Sent from my CPH1851 using Tapatalk

  16. #51
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    Default Re: Air rudder for a big rowboat?

    Yes it was

  17. #52
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    Default Re: Air rudder for a big rowboat?

    No pictures?

  18. #53
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    Default Re: Air rudder for a big rowboat?

    I'm taking a quick look at possible airfoil sections, using airfoiltools.com.

    If I assume a wing similar to the rough one I made, then the wing is 15" wide (chord width 0.4 m). For airspeeds from 5 to 40 mph (2 to 18 m/s) the Reynolds number, Re, goes from 50,000 to 500,000. Check me here: http://airfoiltools.com/calculator/r...&yt0=Calculate

    Looking just at symmetrical NACA 4 digit airfoils, in general the thicker ones generate more lift out to steeper angles. The limit is that the thickest ones go high drag at low airspeeds (flow must go turbulent here). A decent compromise looks like at about NACA 0015: http://airfoiltools.com/airfoil/deta...il=naca0015-il

    Lift to drag (Cl/Cd) is high out to 20 degrees, and it is well behaved without stalling over this range of angles and Reynolds numbers. Looks pretty easy to plot and make also. What do you guys think?

  19. #54
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    Default Re: Air rudder for a big rowboat?

    Your blade will always work at low angle, I would go this way and choose the thinnest...

  20. #55
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    Default Re: Air rudder for a big rowboat?

    Quote Originally Posted by L'Ankou View Post
    Your blade will always work at low angle, I would go this way and choose the thinnest...
    In testing it would get off angle, I think this needs more angle range than an aircraft wing. The drag coefficient on axis is very low for all these foils, in any case. And I want to use a simple rod support, the foil needs to be thick enough for a sturdy rod.

  21. #56
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    Default Re: Air rudder for a big rowboat?

    I agree with that thinking. The wind is shifty and boats get pushed around a lot. You don't want the foil stalling out and acting like a brake. I don't know the science, but I thought that foils with a shorter chord tolerate higher angles of attack, even at a given thickness ratio? Which is to suppose that for a given NACA section, and a given total wing area, one that's twice as long and half as wide will be less prone to stall than the shorter, wider foil. Is this so, or is my thinking muddled? Beside that point, I do understand that the longer option creates more lift on account of reduced turbulence off the tip relative to blade area.
    -Dave

  22. #57
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    Default Re: Air rudder for a big rowboat?

    Quote Originally Posted by Woxbox View Post
    I agree with that thinking. The wind is shifty and boats get pushed around a lot. You don't want the foil stalling out and acting like a brake. I don't know the science, but I thought that foils with a shorter chord tolerate higher angles of attack, even at a given thickness ratio? Which is to suppose that for a given NACA section, and a given total wing area, one that's twice as long and half as wide will be less prone to stall than the shorter, wider foil. Is this so, or is my thinking muddled? Beside that point, I do understand that the longer option creates more lift on account of reduced turbulence off the tip relative to blade area.
    I'm no foil expert, just picking up what I can off the airfoiltools website for now. It shows that Reynolds number scales with the chord width, so a narrower foil has a lower Re. Looking at the curves for the NACA 0015, it shows the drag coefficient is higher at lower Re, and the lift drops at lower angles, not really what we want. In any case, I can manage a 4' long wing but anything longer is getting too big.

  23. #58
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    Default Re: Air rudder for a big rowboat?

    A high aspect ratio foil suffers less from induced drag but lower aspect ratio generally delays the stall until a higher angle of attack.

  24. #59
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    Default Re: Air rudder for a big rowboat?

    Template for a NACA 0015 foil at 15" full width, with a 1.5" diameter hole for a support rod. Say I make 10 of these from 6 mm ply and glue them 4" apart on a 1.5" OD aluminum tube. Then this frame gets a skin covering like a SOF boat. Any better ideas?



    Another question: For this 40" long wing, in worst case 40 mph wind at max lift angle, how much lift will this have? I need to see if the tube will be strong enough, and how much this will pull on the boat.

  25. #60
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    Default Re: Air rudder for a big rowboat?

    To answer my own question, I found this on a NASA website:

    L = (1/2) d v2 s CL


    • L = Lift in pounds
    • d = density of the air. This will change due to altitude. These values can be found in a I.C.A.O. Standard Atmosphere Table.
    • v = velocity of an aircraft expressed in feet per second
    • s = the wing area of an aircraft in square feet
    • CL = Coefficient of lift , which is determined by the type of airfoil and angle of attack.


    Also this for the density:

    I.C.A.O. Standard Atmosphere Table

    Altitude Density
    (Feet) (d)
    0 .002377

    So for d = .002377, s = 4 sq ft, and CL = 1.3 (max from the graph),

    I get lift L = .00618*v2

    At 41 mph, v = 60 ft/sec and L = 22 lb. At 20 mph L = 5.5 lb. This all sounds reasonable. The shaft should handle 22 lb worst case load.

  26. #61
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    Default Re: Air rudder for a big rowboat?

    Nice math. And if the wing gets 90 degrees to a 40 mph wind, what's the stress there? I would guess it would exceed 22 lb. Even so, tube with any wall thickness to it should stand up.

    When you cover the frame, I wouldn't go all SOF technology on it. That would be heavy. I'd think ultralight aircraft -- sew a ripstop nylon sleeve that's a bit small and just stretch it over the framing. Or if you want to get fancy, put a fine nylon zipper on it.
    -Dave

  27. #62
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    Default Re: Air rudder for a big rowboat?

    Go to your local hobby store and buy some "solar film" it's designed for that exact purpose and all you need is a little heat from an iron to fit it.

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