Facet Boat

Discussion in 'Sailboats' started by sharpii2, May 6, 2008.

  1. sharpii2
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    sharpii2 Senior Member

    I like your suggestion.

    I will edit my rules once again.

    A new "Cylindric" development inclusion will look something like this:

    Hulls that are Cylindricly developed, i.e. having curved panels with no twist to them, will be allowed to compete under the following counting stipulations:

    1.) Such boat must have at least 2 curved panels,
    2.) the angles between these curved panels, and any flat ones, which share a joint with them, must be the same along the entire length of that joint, and
    3.) counted as: 14 VF, for the first two Curved Panels, 4 VF for the third, and 1 VF for each Curved Panel, added to that, up to to a total of 8 such curved panels, beyond which the Hull will be considered to be a Round Bottom.

    As I hope you can see, I have put in a VF (Virtual Facet) savings for this type of Hull.

    For example:

    A three Curved Panel Hull, which has some conic development (some twist in at least one of its Curved Panels), will be counted as having 21 VF.

    A Three Curved Panel Hull with no conic development (no twist in any of its Curved Panels) will be counted as having only 18 VF.

    This added inclusion does not conflict with the rest of my system, as the first Curved panel continues to keep its value of 8 VF, which I believe is essential for counting straight-sided scows.
     
  2. upchurchmr
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    upchurchmr Senior Member

    Why set out to make worse boats?
    Do you think you will ever meet the performance of boats with continuous curvature?

    Why - Why - Why

    You might as well imagine a woman with no curves - Why
     
  3. gggGuest
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    gggGuest ...

    Very fashionable... Seen on every catwalk.

    The reason why I suggested single dimensional curvature and constant chine angles is that what you end up with is a boat that is very easy to build with a minimum of tools. So potentially the end product could be a boat that is no harder to build than a pd racer, but is a dozen times better shaped and a more satisfying finished product.
     
  4. sharpii2
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    sharpii2 Senior Member

    No. That's not the objective.

    The objective is to see how close one can come. Hence the handicap system.

    Also, a boat made of facets or curved panels with no twist, will be far less labor intensive to construct and fit an interior to.

    For a one-off boat the labor time would go way down, but other costs, such as construction materials and outfitting, would remain the same.

    The net effect would still be not only a boat that is less expensive to build, but is also less expensive to maintain and repair.

    Such might be worth a say 5% loss in performance.

    Not everyone is a master craftsman, or rich enough to hire one.
     
  5. upchurchmr
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    upchurchmr Senior Member

    I suggest you look at SeaRunner trimarans, although they probably have some twist.
    How about a Cross 18?

    Or just go back to Bolger

    Twist is really not hard, a piece of plywood twists pretty easy. What is the problem.

    I certainly hope our GGGuest is not justifying this boat suggestion with a catwalk?

    Come to think of it how about Solway dory's boats, or Gumprechts
    [​IMG]
    http://www.duckworksbbs.com/plans/gumprecht/drifter16/index.htm

    What is the point of this? Seems like a well worn trail. Just pick one you like personally.
    I'll leave this alone, have fun.
     
  6. gggGuest
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    gggGuest ...

    Here's a shot

    At a vaguely performance dinghy planing shape. If I'm totally honest I didn't spend enough time to make sure all the lines match in all 3 views, but its not a mile away.

    Don't like the bow much.

    5 panels plus transom and deck. Quite a narrow flat bottom. Two floor panels might permit a nicer bow, or maybe an extra panel each side round the bows somewhere.No idea of dynamics, indeed its not even scaled.

    If you eliminate twist in the panels all the chines are a constant angle, which makes it much easier for the beginner carpenter to get them right.
     

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  7. sharpii2
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    sharpii2 Senior Member

    Interesting 20 VF SAP (Single Arrow Point).

    Your waterlines are a bit off, especially the bottom. It would cross your bottom panel, which is curved on a horizontal axis, at a 90 deg. angle.

    The others would sort of kink, as they cross the chine lines.

    Since there is some flare in the topsides, the stem would have to have a bit of a curve to it too.

    I think it's pretty cool though.

    I suppose this hull plan form is chosen primarily for planing in lumpy seas.

    Am I right?
     
  8. gggGuest
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    gggGuest ...

    Yes, Guilty! I drew it right at the forward end,but forgot to to do the same at the stern.

    Yeah, Those ones onto the topsides aren't too critical for the general look though. Iwas aware, but couldn't be bothered.

    Not sure about that. I'm not getting a curve when I wave bits of paper round the table. The waterlines are pretty straight near the bow.

    That's probably more thought than I really put into it. It seemed as it might be nice to sketch something for the thread, so I took a bit of time out (and then stayed up later than I had intended getting it to that state!) Basically I drew a thruppeny bit approximation of a modern dinghy centre section, then a logical matching stern, and sketched a rocker line I liked the look of. From there it was just a matter of extending things logically, keeping a modern style edge waterplane in mind. The constraints of the flat panels and constant chine angle do limit what you can do quite a bit.

    It might make for a better bow section to bring the topsides chine higher, or have the flat floor wash out before the stem, not at it. Haven't yet thought through the implications of whether that works though. Alternatively, if you had a reverse chine for semi wings so the topside could be more vertical which would reduce the excess bow rake, but that's two extra panels and a complex join or an external stringer.

    At the moment one could have the timber merchant cut the chines at the right angles (170, 125 and 65 degrees) and maybe even build the boat without a proper plane!

    The big challenge with this restriction is getting a nice bow shape I think. Spencer's Firebug, which was what inspired me to think about constant angles, avoids the problem by neat use of a semi scow pram bow. You could argue one mark of a great designer is the ability to evade difficult problems completely!

    Right folks, lets see your solutions for the bow area!
     
  9. gggGuest
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    gggGuest ...

    Another go...

    This is even less carefully sketched than the last, I've moved the chine up a bit on stations 2 and 3 and guessed the likely effects.

    On the stem profile, yes I now think it could be curved if were the "waterlines" were still convex in that area, but modern practice is for very straight waterlines near the bow, and you'd just lose a little bit of above waterline length thus with a curve, but also have a blunter entry on wave penetration, which probably isn't the best of tradeoffs.
     

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  10. sharpii2
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    sharpii2 Senior Member

    I see.

    The waterlines near the bow are quite straight, but they do have some curve to them. It is arguable that the actual stem would have so little curve to it that it might as well be straight. And I suppose, for the purposes of fitting frames and bulk heads in the bow are this might be true. They might need the slightest amount of transverse curve cut into them to fit.

    I did find a cool way to extract stem curves from the sheer in plan view.

    I simply draw a line parallel, to the Center-line (CL), which is set as far away from the Cl as the chine is inboard of the sheer.

    two, I divide the space between thees two lines by at least two or three, if practical.

    Three, I draw one or two lines, between the first two set equal distance apart from the CL, the other line, and each other. I call these lines my "between lines"

    Four, I draw a station line just aft the heal of the stem, in Plan View.

    Five, I draw the Sheer and Chine in profile view, along with the station I drew in the plan view.

    Six, I divide the stem height by the same number I divided the horizontal distance between the Sheer and Chine. I do the same with the station line, in the Profile View.

    Seven, I project the lengths of the "between lines" (from the Plan View station to the Plan View stem) onto the Profile View.

    Attached is one curve I drew using this method.

    The biggest problem I have found with "cylinderic development" is that it is impossible to draw a sharp fore foot.

    With your design, it might be best to run your bottom panel dead flat (parallel to the waterline), forward of the maximum depth.

    This would give you a very slight "V" section between where it runs out and the heel of the stem.

    That may not do much for pounding, in a chop, but may do a lot for slapping at anchor.
     

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  11. gggGuest
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    gggGuest ...

    Thinking about full size boat building for the amateur with limited tools, it would, I think, perhaps make sense to just let the stringers run straight from the last frame and and just let them into a piece of stripwood as a stem piece. Not going to be the easiest part of the build actually, but then it usually isn't. A vestigial pram bow might be easier.
     
  12. sharpii2
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    sharpii2 Senior Member

    For ease of amateur construction, the designer has to do more work.

    With a professionally built boat, all the designer has to do is provide a section drawing, a lines drawing, a construction drawing, and a table of offsets.

    For an amateur builder expanded panel drawings, for the sides and bottom of the boat are needed.

    If the panels are drawn correctly and drawn full size and cut correctly, the whole boat will go together with considerable ease.

    But the frames and bulkheads also have to be correctly drawn with considerable detail, so they will fit within the hull envelope correctly. And this will only work if the panel thicknesses, the builder uses, are exactly same as the designer intended.

    To draw a correct bow transom, you will have to draw a good number of waterlines in both Plan and Profile view. These waterlines will almost certainly produce a somewhat curved stem in the profile view.

    The transom will have to be set back some distance from where these lines meet, creating a somewhat shorter boat.

    This bow transom will have curved sides, in section view. But all the vertical frames and bulkheads behind it will have straight edges in section view.

    So, to get the boat to be the exact length you want it to be, you will have to do these drawings twice.

    First, to find out how much length will be lost.

    Second, to draw the waterlines longer to make up for this.

    This is what you get when you join two cured planes at a double angle (one in Plan view and one in Section view).
     
  13. gggGuest
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    gggGuest ...

    By vestigial bow transom I was thinking no wider than it takes for the stringers to come in side by side without all the hassle of tapering them off. Maybe narrow enough to glue a sacrificial soft wood capping on and round it off.

    I think probably for a craft of this nature built in this manner I'd take my drawn lines to be the inner side of the skin, not the outer, and not worry about the last few millimetres. That ought to mean it would be reasonably easy to get the frames laser cut from ply and all the stringer cutouts completely fair. Similarly as long as stations one to transom were where I'd drawn them and fair, if the bow ended up 5mm longer or shorter, then why would I care about exact length? Not going to make any difference to how it handles! Just let the die lie as it drops.

    I remember seeing a set of lines drawn by a very well respected and successful professional design company for a development class with a vertical bow, and rather than agonise over drawing the last two inches exactly right they had simply drawn the lines with a nominal slightly raked bow mostly a bit beyond the nominal length, which was to be truncated at say +2", leaving a nominal (< one inch at forefoot, about two inch at deck) transom bow and the builder to just fair in the last bit of the mould by hand, which was what would probably have to happen anyway in those days. It impressed me greatly as being practical, cheap, and liable to end up with a better result than letting the last two inches potentially influence the rest of the hull fairing - the nose wagging the dog might one say? And as the design went on to win a world championships...

    Panel shapes are an interesting thought. Laser cut to exact size one would only need to sand the angles down, but my goodness the frames would need to be positioned precisely without any twist at all. Not that hard to do, I guess if you had a substantial laser cut slot together MDF building jig, but throwing a lot of stuff away like that seems inelegant. I'm always impressed by designs that are largely self jigging with a minimum of extras.

    Maybe I should get the balsa wood and cardboard out?
     
  14. sharpii2
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    sharpii2 Senior Member

    STRAIGHT STEM W/FLAIRED CYLINDRIC DEVELOPMENT

    Ggg, I have just thought of a way to end up with a dead straight stem on your design.

    The idea is to add a dead straight section to each of the bow waterlines. In practice you will be only concerned with two per panel.

    The way to do this is to draw a station at where the lowest waterline hits the Center Line.

    From there you can draw straight lines, starting at this station, which are tangent to the curve.

    Remember, there is really only one curve. And it is being used over and over again, so a straight line, that is tangent to the lowest occurrence of the curve, will be tangent to later occurrences. The straight lines should all end up being parallel to one another.

    The only possible drawback is the slope of the Stem may end up being different than what you originally intended. But this is how it goes with cylindrical development. You only get to choose either waterline Length, or the Hull Length, but never both. To shorten the Length difference, between the LWL and the Hull Length, a "V" shaped transom could now be used.

    In building the boat, or even building just a model of it, you will probably have to resort stiffeners to insure the panel does not bend in that region. These stiffeners can come together to make extremely strong Breast Hooks, so the only timber you will need will be filler pieces between them.
     

  15. gggGuest
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    gggGuest ...

    Yep, that's what I was trying to say.
     
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