Pivoting sponsons/pontoons

Discussion in 'Stability' started by Horton HCCI, Aug 14, 2021.

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  1. Horton HCCI
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    Horton HCCI Junior Member

    In a trimaran or proa (for instance), has anyone ever considered attaching an outrigger sponson or pontoon to a single supporting boom (strut) using an axle and bearing(s)? My idea is to allow the sponson to pivot around its attachment point to negotiate going over waves, while remaining in contact with the water to maintain steady buoyancy and reduce pitching and pounding, as well as reduce torsion loads on sponson, boom, and central hull. If the principle proved sound, one could also allow rotation around a longitudinal axis, mitigating roll forces in the same way. Using a connecting yoke such as are used in power takeoffs for tractors would seem to allow free movement in pitch and roll axes while still disallowing yaw on the sponson. One might incorporate a pair of torsion springs to oppose extreme rotations and encourage a "normal," steady-state, flat-water orientation when springs are relaxed.

    https://www.napaonline.com/en/p/BK_...hK7b3pAdzaXhqs0owhoCjioQAvD_BwE&gclsrc=aw.ds&
     
    Last edited: Aug 14, 2021
  2. BlueBell
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    BlueBell "Whatever..."

    From the new member in the mile high city, welcome.

    Interesting concept. I get the pitching "gain" but I'm missing the "roll" gain... why?
     
  3. Horton HCCI
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    Horton HCCI Junior Member

    Bluebell--thanks for the welcome!

    As for the "roll" gain--one embodiment I'm considering is a fairly high-speed planing craft, such that the sponsons would be relatively wide, hard-chined, and flat-bottomed. As such, they'd present a pretty harsh encounter when hitting waves on the bow quarter, and that's one thing I'm trying to alleviate. I'm actually imagining a craft (sail, motor, or rowboat(!)) with three roughly equally-sized sponsons (pods) substituting for a hull, a la Vestas Sailrocket 2 or Yellow Pages Endeavor. Here is a "quad" version of kind of craft I have in mind, if that helps: Wiebel Sailing (wiebel-sailing.com). As you can see, and as I think they mention, torsion forces are a considerable concern for them. Free their pods to pivot around as they like and I think this would be less of a problem. What I don't know is whether and how it would affect planing behavior.
     
  4. BlueBell
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    BlueBell "Whatever..."

    Ahaaaaa, I see.

    Okay, planing should be fine but I suspect you're going to need (as you mentioned) a dampening system.
    Making that system adjustable could be of huge importance.

    Is it simply removing the torsional loads you're after?
    Because they add more than they take away in my opinion.
    What is the goal? To go as fast as possible?

    Even pivoting, the loads while on plane are still large.
    It's going to come down to effective damping.
    Max loading really won't change that much.
    Impact loading could escalate.
    Is it worth the added weight and complexity.
    There's the R&D time and expense to consider as well.
    I'm curious what others have to say.
    Cheers!
     
  5. Kayakmarathon
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    Kayakmarathon Junior Member

    Torsion on the Wiebel is definitely a concern. The pontoons have two drawbacks: drag at lower speeds (displacement mode) will be much greater than catamaran configuration of equal length water line, and the alignment of the pontoons will require periodic adjustment.

    As far as trying to solve the water surface tracking problem, it requires a computer and electro-mechanical actuators because there are multiple variables" boat speed, wave height, wave length, and boat angle into the wave front. For a complete control system, pitch, roll, yaw, and their rates of changes and accelerations would be considered.

    These are the problems PhD thesis in control systems are made of.
     
  6. Horton HCCI
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    Horton HCCI Junior Member

    Thanks, BlueBell--good input on damping and its likely effect on planing. In what way could allowing pitch- and roll- motion escalate impact loading? And why adjustable? For experimentation, or to handle different conditions?

    As for the goal, once upon a time it was to avoid digging a long leeward outrigger pontoon into the water on a fairly heavy, conventional, displacement trimaran. I wanted to alleviate (hypothetical?) torsion forces from encountering waves whose wavelength is shorter than waterline length, and in which the outriggers might be on a different part of a wave, or on another wave, than the much heavier hull.

    Goal later became to incorporate this "universal joint" attachment into a three-pod planing sailboat (wingboat), again to reduce twisting stress on the structure when spanning waves, keep the overall boat flatter, reduce impact when negotiating chop, and perhaps do a better job of keeping the pods in contact with the water, thinking this might help with maintaining the plane.

    Current project (thought experiment, mostly, but I'm trying a model) is to transfer the three-planing pod idea to an extremely outre racing rowboat (scull), target weight about 35 lbs, target speed as fast as humanly possible. (Literally.) The universal-joint attachment might not provide much value here, as weight and speed are comparatively quite low, and any record attempt would be on calm, flat water. But if the thing showed any promise as a recreational craft, maybe the joints would make it handle heavier seas better, or be less likely to twist or break the booms. (Yeah, it has booms. Long, spindly ones.)

    Here is a pretty good approximation of the idea, minus the method of propulsion (I'm not using an air prop): . (I love this guy.) Skims and skips along nicely, but who knows what it would do with any ripples bigger than that pond? It's basically a three-point hydroplane, and we know their problems. Maybe pivoting sponsons would help?

    Weight, R+D, cost not an issue right now--if it gets beyond a model, the prototype will be plywood and some aluminum tubing, maybe a few cannibalized second-hand rowing machines. Joint itself is butt-simple for this size and power of craft.
     
  7. Barry
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    Barry Senior Member



    is this what you are after???
     
  8. BlueBell
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    BlueBell "Whatever..."

    You are most welcome.
    Undamped travel will result in a bang at the end it's range of motion.
    Yes, all of the above.

    My thoughts went immediately to Kayakmarathon's comments about electronic/servo control when I first read your original post.

    It seems you're focused on one design idea.
    I don't think it's a "silver-bullet" or "cure-all" for structural robustness.
    But what do I know.
     
  9. Horton HCCI
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    Horton HCCI Junior Member

    Kayakmarathon--Thanks for your input! As my response to BlueBell indicates, I was initially envisioning a big, seagoing trimaran (not that I could ever afford one) or a record-challenging sailboat (ditto). This was many, many years ago. I suppose the idea could still apply to such things, if there is any problem to address or if it would make any contribution toward addressing it. But my sights are now set on much smaller, more readily doable things. Anyone who is interested and wants to do a doctoral thesis on control systems for pivoting sponsons/pontoons, more power to 'em, and welcome.

    I hear you on planing pods facing challenges of high skin drag at displacement speeds, but I feel the neeeed for speeeed. You cannot win a human-powered watercraft competition in a displacement boat, even a cat. You need a hydrofoil, or better, I believe, hydroplane. Since as a human rower I have next to no power available to me to pop up onto a plane, I need my craft to be featherlight--my booms (akas) can't weigh more than about 5 lbs apiece, if that. They can't be allowed to twist, bend, or break. However, since I can't afford exotic materials (which would be foolhardy in a prototype anyway), I need to try to unload stresses rather than overcome them with "brute" materials strength or beefiness. Hence the wonderment about whether pivoting/rolling sponsons could help with this.
     
  10. Horton HCCI
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    Horton HCCI Junior Member

    Barry--YES!!! That is EXACTLY what I'm after!!! Thank you! Especially around 3:16, where they have a runabout version. Four pods, out on booms. So someone has done it. Looks like it does exactly what I thought it would--tame the pounding and roll. And I now understand from BlueBell why I need dampers, not springs. Or perhaps both. Struts, basically.

    Well, thanks, guys! That's really helpful. Not to be dismissive of electronic/servo control, but I'm trying to keep this simple and within my capabilities and understanding. What I have is an aquatic bicycle, in essence, so my mind goes to bicycle parts. Specifically, mountain bikes--suspension forks or the seat-to-chainstay strut. Right scale, and they work to make them as light as they can. That should do the trick. And BlueBell's right, I think--roll much less of a concern than pitch, particularly as it has a very wide stance. I see a race version without struts, and a "seafaring" version with. Oh, that's just dandy. Thing's progressing apace. Thanks again, all.
     
  11. gonzo
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    gonzo Senior Member

    The Gougeon brothers built trimarans with flexible mounts in the mid 70's. There have been others too.
     
  12. Horton HCCI
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    Horton HCCI Junior Member

    Actually, another analogy that comes to mind is a snowmobile. Right? It's a three-point hydroplane, it's just that its "hydro" is frozen into crystals and spread over bumpy ground. I wonder how it keeps its skis planing while still hinging them so they can follow the contours of the ground and navigate drifts. I assume they plane. How else could they float over deep snow?
     
  13. Horton HCCI
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    Horton HCCI Junior Member

  14. gonzo
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    gonzo Senior Member

    Skies spread the weight over a large surface to prevent sinking in the snow, which is different from buoyancy and dynamic lift (as in planing).
     

  15. philSweet
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    philSweet Senior Member

    @ Gonzo, If I remember correctly, after a couple of false starts breaking wooden springs, they bolted on a set of McPherson struts from the nearest autoparts store and made an attempt on the absolute sailing speed record that way. I think there's an article in Wooden Boat about it, but that was a looong time ago.
     
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