tapered strips

Discussion in 'Boat Design' started by JackWhite, Oct 10, 2009.

  1. JackWhite
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    JackWhite New Member

    Anybody attempted using tapered strips for pulling boat design (a scull or rangeley?) I pondered using a strip narrow at the ends say 4-5mm (or less) and say 6-8mm in the middle where there is more stress from pulling. Just a thought.
     
  2. PAR
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    PAR Yacht Designer/Builder

    What . . . ?

    Is there something you're trying to ask or say or . . . What . . .?
     
  3. apex1

    apex1 Guest

    That was just a misunderstanding I guess!
    It is not pulling the boat by strip, it is stripping the boat by pull!
     
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    Sounds like an idea to try at least, if you're really serious about reducing hull weight. You could also consider varying the thickness so it's max at the high stress locations of sheer and keel and less elsewhere.

    I have been pondering the problem of accurately tapering the thickness and/or width of thin strips for various applications such as strip-built hulls and hollow masts but I haven't yet solved the practical issues. Hopefully someone out there has a method that will work without an elaborate shop setup. Otherwise it might be simpler to just build with constant thickness strips and plane off what you don't need.
     
  5. apex1

    apex1 Guest

    Terry I am deeply impressed! Chapeaux......
    How could you understand that?
     
  6. PAR
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    PAR Yacht Designer/Builder

    With a column, such as what Terry is suggesting (mast), it's done, I've done it and fairly easy to calculate, but a hull? Maybe a very small boat, free standing rig, etc. On a pulling boat you'd have some interesting load paths on the socket locations, foot braces and a number of other, not so easily accounted for strains.

    Maybe a more specific set of questions on a particular design would be more helpful.
     
  7. JackWhite
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    JackWhite New Member

    I was thinking using a jig. Using a long 2x4 shaped with a long arc with the end result being a strip with a thick middle and thinner at the ends. one side curved and the other straight. This probably would work best with a band saw.
     
  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    Piece of cake, Richard, with a background in Aerospace I've seen far worse statements of requirements.

    My favorite specification was for a communication equipment. The customer's engineer had decided he knew best how to meet one of the requirements so he specified HOW it should be done rather than WHAT should be done. Definitely a no no, compounded by the fact that his design would have disabled the entire system long before the conditions reached the point where that was necessary. He could not be convinced, so we put in the ciruit he wanted and demonstrated it did what he wanted it to do. He never noticed another circuit which detected when his device was going to take down the rest of the system, and sent a disabling signal to it. So between the two circuits, they did absolutely nothing. The customer bought several hundred and I heard they are still in service nearly 40 years later.

    Then there was the mining company that rejected my $2.7M bid "too expensive we can do it cheaper ourselves" ... several months later they had successfully wrestled the cost down to $8M. Subsequently they decided that wasn't what they wanted after all. As a result several promotions were handed out, not unfortunately in my neck of the woods though.
     
  9. messabout
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    messabout Senior Member

    Let us say that you will strip build a Rangeley, Adirondack or some such. Suppose it is an 18 footer. The presumption is that you will minimize weight. Quarter inch thick strips could be tapered to one eigth at the ends. You would have saved about 10 cubic inches of wood on a 1/4 x 3/4 strip. That'll come to something like 12 pounds for the whole boat. Alas, you will be using more glass,kevlar, or carbon on the thin ends. Net result; not much total weight saving. Contrast weight saving with the amount of work and complication and then decide whether it is worth it.

    A tapered strip mast, as someone mentioned, is a whole different deal. The hassle might be worth the trouble on a mast, because aloft weight is to be minimized in spite of complication.
     
  10. ancient kayaker
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    ancient kayaker aka Terry Haines

    Simpler to use foam core?
     
  11. PAR
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    PAR Yacht Designer/Builder

    The thinner dimension strips also dramatically reduces the radius of gyration in these areas, thus decreasing several aspects of this type of construction, particularly cored builds.
     
  12. ancient kayaker
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    ancient kayaker aka Terry Haines

    If you reduce thickness to half at the ends, you can save only 25% even with a straight taper; with a circular arc on one side your saving will be half of that. Considering the other material in the boat, you will be lucky to get a weight reduction of much more than 5%.
     
  13. nordvindcrew
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    nordvindcrew Senior Member

    I measured the girth of my current boat at the stations and calcutated how many 1"wide strips were needed at the maximum beam/girth. The different measurements from the other stations were calculated and a pattern piece hand planed . A router with an edging bit trimmed the other strips. A test was not too successful. I hoped to eliminate the straight lines of strip planking wih something that looked more traditionally planked. I got some real funkey lines down near the keel that eventually ran somewhat as hoped as I worked towards the sheer. Gave up on the idea
     
  14. ancient kayaker
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    ancient kayaker aka Terry Haines

    It's just not as easy as it sounds, is it Jeff?

    After I tried it I concluded that to taper the width it was necessary to taper the thickness of the mother plank first, by passing it through a thickness planer on a backing board with different thickness spacers to hold it at an incline. Lacking a thickness planer that experiment did not proceed. I hoped it would eliminate the heavily-tapered partial-length strips that need to be cut in with great care on the bottom of a strip-built hull.

    I could not persuade a saw to cut the strips with a decent taper on the thickness, even one way as for a hollow mast. I think it would be necessary to make a snug-fitting jig, perhaps a larger plank with a rabbet same width as the strip, tapered if necessary, cut the strip constant thickness and plane it, with a vacuum hold-down of some kind to hold it in place while planing or routing. Too complicated for my taste. I can plane a 1:6 or 1:12 scarf bevel but 1:/400 is out of my league.
     

  15. nordvindcrew
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    nordvindcrew Senior Member

    I jointed a 2X6 ,rabbeted it out to be a snug fit for the sprips then planed it to conform to the taper I wanted on the strips. A router with a laminate trimming bit ran along the planed edge and brought the strips to the desired shape. It worked, but as I noted, the run of the "planks" was a bit funky at the keel and eventuallly sort of ran the way I wanted at the turn of the bilge. This was not a real build, just a partial done on a set of molds I had.
     
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