Tortured ply for Herreshoff 12-1/2?

Discussion in 'Boat Design' started by ancient kayaker, Oct 19, 2012.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    When Bolger designed a plywood version of the elegant Herreshoff 12-1/2, he reduced the freeboard “to distract the eye from the coarser sectional shape” but admitted “it will work from some angles but not all.”

    Earlier this year LP was experimenting with tortured ply. He glued stringers to a flat sheer plank, on the inside near the centerline and on the outside at the sheerline and chine. When the panel was bent around the sheer curve the ply was forced to form a belly which is easily seen at http://www.boatdesign.net/forums/wo...on/15-lapstrake-kayak-40486-2.html#post523920

    It occurred to me that LP’s idea could be adopted to improve the above-the-waterline appearance of the Bolger plywood 12-1/2. The “belly curve” limit should be about the same as for bending plywood in one direction: according to data supplied by PAR that is a bend radius about 100x thickness. For a compound curve that limit would apply to the curve in both bend directions, to a first approximation at least.

    In the figure the midship sections of the Bolger and Herreshoff designs are shown on the left of the centerline. On the right the Bolger section has been modified to introduce a compound curve into the sheer plank. In practice a designer might wish to get closer to the Herreshoff outline, perhaps restoring the freeboard reducing the BWL, but I want to keep it simple at this time.

    The curve in the vertical plane (i.e., the “belly” curve) has a radius of 87", which would not be a problem. The Bolger and Somes Sound boats are - I believe - built with 3/8" ply, but the compound curve and stringers would add considerable stiffness and strength so I suggest that 1/4" ply could be used. The curve in the horizontal plane has a radius of approximately 16', and the belly depth parallel to the radius is about 1.4" or 0.7% of the radius, which is within the ply bending guidelines provided by PAR.

    So the idea should work. It would require some experimentation or finite element analysis first. I wouldn’t start from the Bolger design though, with all respect to the master of plywood design it was compromised too much and the Herreshoff is a nicer looking boat.
     

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  2. PAR
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    PAR Yacht Designer/Builder

    The Bolger version looked fine in profile, but that was about it, honestly. A molded plywood approach might be a better way. You could have the sweet shapes and a plywood build. A couple of layers of 1/8" Okoume for the topside, maybe 3 for the bottom. Not the tortured method, but you'd also not be preloading the panels during installation either. An inner sheath with biax will stiffen the panels up enough to fill out the scantlings.

    The significant, yet unacknowledged changes Bolger made to the 12 1/2 where to firm her up, for the modern sailor and I think this could be taken further, particularly with a stripped or molded build. This would tend to reduce wetted surface and if coupled with a reasonable ballast/displacement ratio, down low, she'd be a better boat, again for the modern, use to sailing flatter, sailor.
     
  3. Ilan Voyager
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    Ilan Voyager Senior Member

    Very few monohulls can be built in compounded plywood, as there is too much compound because of the beam/length.
    The 1/4 plywood is 8 times stiffer than the 1/8...so imagine trying to ploy that plate. If not convinced or wanting to try the method the chapter 24 of the book Gougeon Brothers on boat construction will give you the methodology for trials at scale 1/12
    .
    There are also methods with fiber added outside before bending (Stressform by the Gougeon) and/or with strategic cuts mainly at the chine of the aft part.
    But that gives shapes very different of those of the 12-1/2 and it's totally allergic to long keels and wine cup shapes.

    Conclusion PAR is right.
     
  4. PAR
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    PAR Yacht Designer/Builder

    The 12 1/2 could be diagonally double planked with 1/8 or 1/4" plywood, though the reverses along the garboard will test your will, thin plywood is fairly compliant. It could also be diagonally single planked with a sheath inside and out to accommodate the needed stiffness.
     
  5. ancient kayaker
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    ancient kayaker aka Terry Haines

    PAR: well you know me by now - always looking for an easy but different way! For me the attraction of the Bolger was it's extreme build simplicity; the Somes Sound design also has a nice plywood lapstrake approach but is more complex. Diagonal double planking would look great but would be an even greater departure from build simplicity. You're right about the Bolger's looks but it has its fans and sails well by all accounts; I tried to preserve its greater beam in my sketch.


    Ilan: you and PAR both make a good point about pre-loading the panels. Based on an energy total method I estimate the force required to form the compound shape in the sheer plank will be x5 the force to form the sheer plank in the original Bolger design, using the same thickness ply, but the thickness can be reduced given the use of stringers.


    As an adaptation of the Bolger 12-1/2 rather than the Herreshoff or Haven, I was inclined to make as few changes as possible, just using tortured ply for the sheer plank which is very slab-sided in the Bolger design. That would remove the slab-sided look midships and soften the visible chines aft and for'd. The effect of the change on the chine seam would make the build more like a lapstrake build than a hard chine one; it would require considerably more work to evaluate that.

    Does anyone know where I can get study plans for the Bolger 12-1/2?
     
  6. Ilan Voyager
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    Ilan Voyager Senior Member

    It's practically impossible to make such a boat in compounded, unless using latex plywood. It's pure geometry and topological coefficients of curvature. More, compounded is allergic to reverse curves, the second derivatives of the curves equations cannot change of sign. Or the hull is all positive surface or all negative one. But not wine cup shapes.

    Make a model at 1/12 and you'll understand visually the tensors of the surface defining the volume.

    If you want a monohull in compounded you have to design a boat for this method.

    As PAR wrote; for a boat designed for classic wood, the best alternative is diagonal planking with something easy to ploy like plywood. 2*1/8 plus glass. That would light and strong and not very hard to make. I'm afraid that the 1/4 will need some persuasion with hot water and vapor...the curves are surely tight at the keel plus a reverse.
    Another possibility is strip plank 3/8* 1 1/2 and glass; pretty tedious work.

    Morality when it's designed for classic wood, most of the time it's very difficult to have an alternate method except polyester.
     
  7. ancient kayaker
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    ancient kayaker aka Terry Haines

    Ilan: you are not understanding the concept or you do not know the Boger design. The lines can be seen in part here http://www.flickr.com/photos/hallman/tags/plywood125/

    Take a Bolger 12-1/2, strip off the slab-sided sheer plank only, replace that with a tortured ply panel, and you have my idea. I do not suggest changing anything below the sheer plank, and the Vee-bottom and keel remains just as Bolger designed it. In the above net site there is a drawing of the sheer plank developments, which are almost straight: that should simplify the bending step.

    Bolger's sheer plank is curved in one axis only, the curve is a cylinder, not even a conic. There is no reverse curvature in the sheer plank and only a very little in the garboards, which I do not propose to change.
     
  8. Ilan Voyager
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    Ilan Voyager Senior Member

    I was taking the about Herreshoff plan.
    The Bolger is a hard chine boat as I see on the pics. So compounding is out of the subject. You screw and glue directly on the frame.
    The wetted surface is so monstrous that my poor old eyes are sore. (bad joke, but the boat is truly ugly when you see the smoothness of the original Herreshoff...I know, it's a very personal opinion and nobody has the obligation to share it).
    Sincerely what's the interest to build that?
    The Bolger is rather ugly and nobody will be in extasis looking at it. I doubt that its performances, sensitivity of steering, ability of going upwind and others are remarkable. That I'm sure it's painfully slow.
    The Herreshoff is old, very old, extremely old and has the performances of his time...Even if Nathaniel was a genius, the boat shows its great age, like a Ford T or a Deperdussin 1913 plane.
    Hundreds of similar boats have been drawn, almost indistinguishable, with similar performances. In a time where there was no possibility of trailering, each club had its small boat. The old sailors speak highly of them, and in reality there are speaking of their youth. Everything was better before, when they were young; the sun shined more, the sky was bluer, the beer better, the girls nicer and the boats were fast, easy, and dry. Nostalgia is not more what it was.

    For the same amount of money and maybe less work, you can make a ballasted dinghy more stable (and unsinkable...) with the great advantage that trailering it will be x times easier, plus no worries at low tide. And we do not talk of perfs, nor pleasure at the steer. It can even be pretty playing with the paints and varnishes, and adding a little retro touch, like the cockpit.

    What do you objectively find in these designs? Prices? it's not a good criteria. What is worth to spend time on then? It's a mystery for me, I do not want to die stupid. Give me some clues please.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Yep, you're correct Terry, the compounds would be possible and easily within the tolerances for the panel data I provided some time ago. The garboards, as you've identified would pose the most difficulty, but not insurmountable. In fact, it would probably be reasonably easy.

    On single skin approaches, which I'll assume is your goal, I think slitting the panel and either a pie wedge shaped filler or just a really fat gaped Payson butt joint will prove easier and offer much more shape options as well. I'd be inclined to fit a pie wedge and butt join them. The Bolger 12 1/2 is just screaming for more panels frankly.

    Bolger and Friends (Susan) still have control over his plans, though I've gotten nothing but a mixed bag in regard to getting her to move plans. Some have had good luck, others no reply to inquiries.

    The original and subsequent versions of the "boy's boat" (12 1/2) actually is a fine little sailor, light on it's feet, agile and very solid in varying conditions. Joel White's (Haven) rendition is a better boat if you need shoal draft.
     
  10. ancient kayaker
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    ancient kayaker aka Terry Haines

    - The Herreshoff and the Haven are such lovely boats, it seems pity that Bolger was so obsessed about his ply box approach that he produced such an ugly design. However, some people are still building it are like it’s performance. It would be nice to offer them something better to look at . . .


    - It’s not objective, it’s subjective, very much so. The Herreshoff and the Haven are both elegant but challenging to build, the Bolger is ugly but easy to build, wouldn’t it be nice to see something with the best of both?

    I like improving things. Perhaps I’m as obsessed In my way as Bolger was in his? BTW the performance of these three boats (and the similar Somes Sound) is quite decent. By all accounts they compare well with present-day boats of the same class. Obviously they don’t plane so it is pointless comparing them with a dinghy for example.


    - I’m hoping it can be done with a single uncut ply piece.


    - - agree in spades. Too Bolgeresque by far . . .


    Thanks for the interest you have both shown in this wacky idea. When I get my workshop sorted out again after a recent spate of non-boat-related construction I'll try to test it out at a 1/2 or 1/3 scale; I think I have some suitable ply. From my analysis so far I suspect the main problem - apart from the potential force required - will be failure of the stringers due to the sectional width required to achieve the "belly" depth; that may prove the limitation on what can be achieved with the concept.
     
  11. Ilan Voyager
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    Ilan Voyager Senior Member

    Yes, totally subjective so I won't bother you with that as we have very different approaches. Each one as honorable as the other. If we thought all in the same it would be very boring.

    I'm interested in old boats when they represent a step in naval architecture and engineering. For example for me the most interesting boats by Herreshoff are Gloriana (structure engineering) and his catamarans. The class J are big and beautiful but nothing more, not really interesting, except for the winches. Yes the most interesting part of Reliance were the winches, so good that they were used on Ranger in 1937! But I do not feel any wish to build an old design, as I do know its limitations. They do not fulfill my requirements.

    I'm more utilitarian, and more interested by a boat as fast as possible, funny and safe to sail. In fact I was more interested by designing, building and tuning it. When it have had given all its juice, I was bored by the boat and it was sold. And I was thinking about the new project...

    Good luck but please the Bolger is truly too ugly.
     
  12. PAR
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    PAR Yacht Designer/Builder

    With a 12.5' LWL, they're not going to be quick as keel boats go. They where intended as a basic boat a boy could learn to sail in, without growing tired of it the following season. The area they were intended to sail suits the design quite well, as it handles the short, often steep chop of the bay very well, with good manors and predictable response. I'm not sure of it's rate, but a 115 would be about right for a boat of this size and configuration. They are perfectly balanced and a pleasure to sail on all points. If you want a Corvette, don't buy a Buick.
     
  13. ancient kayaker
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    ancient kayaker aka Terry Haines

    Ilan, I agree with your last post, although you have to admit that the 12-1/2 is Herreshoff's legacy design whether he would like it or not.

    The Bolger is utilitarian in it's own way, although not a performance boat. My point was, since people apparently still build them, it would be an act of charity to make it look a little nicer. I'm not interested in building one BTW . . .
     

  14. ancient kayaker
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    ancient kayaker aka Terry Haines

    - Your comment about needing shoal draft is a good point. As a beach launcher I would prefer a boat with a flat or slightly Vee’d bottom. That would require a more severely compounded curve in the sheer planks.

    Keeping in mind your earlier comment about pre-loading the panels, one way to control the forces would be to over-bend the sheer panel using the inside stringer, outwale and outside chine log per LP’s method, then glue on an inwale and inside chine log to hold the shape, and finally remove the outside chine log before allowing the panel to relax. There would still be strain locked into the plywood but it would be distributed through the length rather than at the stem and transom.


    - no doubt, and it would permit a more severely compounded shape. Rather than slitting the panel where it is under tension it might be safer to slit it along one or both edges - where it under compression. After adding the inside stringer, outwale and outside chine log, a groove could be routed along the outside chine log and darts cut through the log and into the panel. As the panel is bent, a line running in the slot could be tensioned to force the slits close - after gluing them - and increase the depth of the “belly” curve. Adding the inside chine log before the glue sets in the slits should then help to fair out the curve and smooth the “facets.” Slight faceting is more acceptable underwater but if this trick successfully disguises the facets maybe it could be repeated at the gunnel. Another stringer where the slits end might also help hides the facets.

    However, the slits would likely need to be wider than a typical saw kerf though, and maybe even profiled. If so it is getting a bit too complicated IMHO; but I need to try it first to see what happens . . .
     
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