Design Spiral into Madness

Discussion in 'Multihulls' started by Owly, Apr 15, 2021.

  1. Owly
    Joined: Oct 2016
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    Owly Senior Member

    I've never been fettered by convention or conventional thinking. My favorite designers have always been outside the box because I'm inclined that way.... or perhaps the reverse. Rob Denny's Harry Proas fascinate me with his many innovative solutions, but they do not meet my personal criteria, and the reality is that I do not intend to build a voyaging sailboat. There is something to be said for bidirectional boats. I like his cabin integrated with one hull leaving a lot of deck space connecting the fore and aft decks, and the fact that the cabin is on the windward side, basically providing 3 sheltering faces. I like his twin rudders alongside the hull, one fore and one aft, they can act as both a rudder and a leeway device / daggerboard... retractable and kick back. It doesn't hurt that I own a piece of heavy equipment that steers on both ends. Shunting makes sense to me in some circumstances, tacking in others.
    So looking at available cats, we find the Warram family. They are already potentially bidiectional if you remove the rudder and skeg. Mental gymnastics cost nothing! I consider the Ballestron rig absurd. It's great to be able to tack the main and jib together but I object to the bearing mounted rotating mast.......... I just don't like it on a gut level.
    So we start with a Wharram. We integrate a pod with one hull, install HP style rudders, removing the original rudder and skeg. We design it to either shunt or tack......your choice of the moment. You can place the cabin for shade or wind shelter, or for cooling wind, or whatever suits you at that moment. You can sail in either direction. Now comes the rig. What are we going to do for a rig. We are using and loading both hulls. It's not a proa, it's a catamaran that can sail in either direction and shunt or tack. To maintain some semblance of balance we need two masts or one central mast. I propose a schooner biplane rig. Two masts in diagonally opposite corners. I'm seeing free standing masts with camber panel junk rigs. I played with the various possible configurations, and this made the most sense to me, but I'm partial to the junk rig anyway. Making the CLR and the CofE work out in both directions may be a challenge... but not an overwhelming one considering the fore and aft rudders. And of course you would only motor in one direction.... presumably with an outboard... unless you wanted to drag it from one end to the other.
    I don't see any glaring fundamental flaws... I'm not sure there are any compelling benefits either, but it is an interesting exercise.... at least to me.

    H.W.
     
  2. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Build something, then I'll dismiss your work just as easily as you do someone who actually designed, built and sold useful boats.

    Does your gut tell you you don't need boards?

    Why not just run your motor in the reverse direction so you can motor in either direction.
    I can't believe you would just casually dismiss opportunities for improvement.
     
  3. Rumars
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    Rumars Senior Member

  4. upchurchmr
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    upchurchmr Senior Member

    But that one will not go backward as well as forward.
    How can you compare them?

    But I still agree with your evaluation.
     
  5. Rumars
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    Rumars Senior Member

    What's the use of going backwards just as well as forwards? Shunting proas were invented to get over the materials limitations in order to achieve the desired performance. With modern materials the best proa is a catamaran, and we got to the limits of our materials and gone trimaran for high performance boats.
    Anyway, a biplane junk can sail equally well in both directions, the sail revolves around the unstayed mast. What you don't want to do is place the masts diagonally on the end of the hulls, you want to keep the weight nice and central, especially with a double ended hull. What remains is the complication and weight of having four rudders, and miles of rope.
     
  6. Owly
    Joined: Oct 2016
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    Owly Senior Member

    The two Harry Proa style rudders if you are familiar with them in principle, are deep balanced foil type rudders that are retractable like a daggerboard. They are not at the bow and stern, but forward of the stern / aft of the bow, a significant distance. My thinking is that the foreward rudder will stay in the water as needed acting as a leeway device / daggerboard, or what have you. It can also be deployed at an angle as it is a rudder, which should make it more effective as a daggerboard. The Harry Proa typically has two wheels, and you would simply design the rudders as a symmetrical airfoil / hydrofoil, that could be turned 180 deg so that the "fat side" (leading edge) was always leading. There would not as someone suggested, be 4 rudders These rudders are on the inboard side of one hull or the other. For extra turning authority, they could be deployed in opposite directions....... and NO, I do not feel boards are necessary in addition.
     
  7. Owly
    Joined: Oct 2016
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    Owly Senior Member

    Typically a junk rig has the mast forward of where it would be on a Bermuda rig because there is a smaller proportion of the total sail area forward of the mast.... anywhere from about 10% to close to 30%, where on a Bermuda rig it can be closer to 50%.... even more in some cases. On a Bermuda rig, the mast is typically forward of center. In any case, reversing direction completely changes the center of effort. Rob addresses this by either having one or two ballestron rigs. If one it is dead center. A biplane junk rig most definitely will not balance in both directions unless the masts are dead center. The idea was that the masts needed to be fore and aft to achieve balance when reversing direction... keeping the center of effort in the proper relation to the center of lateral resistance. Basically a schooner rig. All I'm proposing is a schooner rig, but as it is not realistic to place two free standing masts between the hulls, the choice is to place both on one hull, or one on each. I did not mean to imply that the masts were at the far ends of the hulls. I would envision them being about 1/3 of the hull length from each end.... Centered would work, but it would be a nuisance.
     
  8. Owly
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    Owly Senior Member

    Of course this is a "just for fun" exercise, not a serious proposal.... Something far from convention to play with mentally and in napkin sketches. To find the problems and to solve them..... Perhaps make a model to play with. Of course reversing your outboard would work in a marina or short distances.... for motoring any significant distance, I would imagine that one would want to run the outboard in forward.
     
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  9. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    I think the best proa would be a proa with a parafoil sail.
     
  10. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    Just rotate the outboard ?
     
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  11. DogCavalry
    Joined: Sep 2019
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    DogCavalry I aim to misbehave.

    Where I live there are log booms in the river constantly. They manage them with a little beast they call a boom boat. They have an outboard in a turntable they can spin 360°. It's pretty cool.
     
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  12. Owly
    Joined: Oct 2016
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    Owly Senior Member

    This really isn't a proa.... It's merely a bidirectional catamaran.... But I've always wondered why the PF sail isn't more common... a great "insurance policy". I've always viewed standing rigging as a veritable house of cards... Only a single component of dozens has to fail to dismast you. I'm not sure how well a parafoil sail works in the real world... it does take very little to keep one inflated. I know one man who flies paragliders in Hell's Canyon..... He calls it "sky camping", and often takes multi day trips, landing in the evening, goofing off in the morning, launching in afternoon afternoon, and eventually climbing to an altitude where he can call his wife to pick him up.
    H.W.
     
  13. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    This forum is called "boatdesign". That includes the more mundane considerations of scantlings and the minutia or hullforms, but it probably also includes thinking outside the box.

    A lot of "unusual" ideas come to nothing, but some lead to viable alternatives and even broadly applicable improvements.

    An unusual thought makes a refreshing change from the usual "I want to build a 40' catamaran but don't want too believe it'll take 10 years $300k and destroy my marraige". Maybe sailing a catamaran backwards using diagonally positioned masts will come to nothing, but where's the harm in talking about it ?

    FWIW I'd suggest you build a little one and have a play. See what happens. Build it out of rubbish, just big enough to carry you. Drop it in a shallow lake so you can get out and walk to shore. See what happens.

    Looking forward to the sail report.
     
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  14. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    I brought up parafoils because there are still techniques that theoretically should have advantages but for which no easy practical solutions exist yet to make use of them. Like parafoils and hydrofoils and WIG craft and solar powered boats.

    So if you are looking to "go exploring" in imaginary designland to find new solutions to unspecified problems (which is fun, I agree) then maybe those areas are more fruitful? :)

    Or, what is the design goal or the problem you are trying to solve with a bidirectional catamaran? A river ferry seems like a pretty good example for where it might make sense though.
     

  15. Will Gilmore
    Joined: Aug 2017
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    Will Gilmore Senior Member

    I would like to see a sketch or two.
     
    BlueBell likes this.
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