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Thread: New design, 6'10" lapstrake pram, "Lucky 13"

  1. #1

    Default New design, 6'10" lapstrake pram, "Lucky 13"

    Sharing a design for a lapstrake pram I am presently working on. Made of 13 strakes of 1/4 inch plywood, hence the name "Lucky 13". The stations are at 1 foot 2 inch spacing, and the mold cuts from two sheets of 3/4 CDX plywood that interlock. Frames also at 1 ft 2 inch spacing, cut from 3/4" fir.

    http://hallman.org/boats/Lucky13/






  2. #2

    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    Here are a couple shots of a paper model of this pram...




  3. #3
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    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    With that big, vertical, for'd transom only just above the DWL won't she bang, hard on even the smallest waves?


    Sorry to be Cassandra to your Pollyanna.

  4. #4
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    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    I would certainly like to hear about what the intended purpose of this design is. It doesn't look like any small pram I have ever seen.
    Boats this small don't go very well because of the short waterline and giving a small pram a rectangular underbody seems detrimental.
    If you look at common lapstrake hulls they are always rather rounded. That is because the angle between any two planks has to fall within a narrow range of angles in order to have a sufficient flat for the attachment point. What you have is a flat bottom with hard turn at the bilge which I don't think will accept coverage with lapstrake planks.
    Last edited by Cuyahoga Chuck; 05-07-2011 at 12:34 PM.

  5. #5
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    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    Which end is the snout?

    Chuck, I think this could be built in glued lapstrake just fine with a big, wide center panel. I would definitely have concerns about that extra-wide bow transom carried so low to the waterline. I think you'll likely need to make it smaller, increase the rocker at the bow or rake it more-- or all three!-- in order to get a boat that will tow safely in a seaway. The evolution of the small pram yacht tender has converged on a particular shape for a reason.

    Of course if this is a duck-pond boat or something like that, then it doesn't matter so much. But if it's to be a genuine tender, you might want to look at the common features all of these known, successful prams have in comparison. I need to tow my own tender everywhere in all conditions because my boat is too small to fit her on deck. The right bow shape will make a world of difference when towing in a seaway.


    Joel White Nutshell Pram:


    Oughtred Granny Pram:


    Gartside 7' Clinker Pram:


    Herreshoff Marco Polo Tender:


    William Atkin Katydidn't:


    My own Dog Ferry pram.
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  6. #6
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    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    Or the shape developed by the people perfecting the boat over several hundred years.

    It really is quite difficult to build an ugly wooden boat.

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  7. #7
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    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    Some very pretty pictures, so far, but not instructive about the joys of the real dinghy world. And S&G is not necessarily pretty but it has it's compensations.
    http://gallery.bateau2.com/displayim...at=10905&pos=0
    Last edited by Cuyahoga Chuck; 05-08-2011 at 02:31 PM.

  8. #8
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    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    I don't understand what you mean by "the joys of the real dinghy world", Chuck. I've used and gone through 7 different tenders to settle towards a round-bilged pram as the best behaved little boat if you must tow in all weathers. Cruder, more simplified shapes and hard chines don't show to their advantage when the wind is over 30 and the swell is on the quarter. If you want a boat that will spin and dodge and slide merrily sideways out from the curl of a breaking wave with unconcerned aplomb, then a hard chine boat like a D5 or a Sabot or the disgracefully horrible to tow Tortoise is sub-optimal.

    The fact that a round-sided lapstrake pram is also awfully cute is really just a bonus.
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  9. #9
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    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    "The joys of the real dinghy world" invovles sailing a bathtub-sized boat upwind a mile even if it takes 15 tacks to do it. And never letting a tow rope touch your bow even if you'll be 2 hours late for supper.

  10. #10

    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    Thanks for the feedback. I just was tweaking to incorporate this feedback, and see significant trade offs. To achieve the rough water, tow-ability, you need to give up displacement and stability. Ending up with a boat that tows better, but weighs more and is more awkward to put on top of an automobile. Also, a boat that would be harder to stand up in, and which would row slower in calm water (but would row faster in rough water). It does still cut from 8 foot sheets of plywood. Here are screenshots of the 'tweaked' more rough water/tow-ability shaped doodles:
    Last edited by brucehallman; 05-09-2011 at 10:40 AM.

  11. #11

    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    Quote Originally Posted by James McMullen View Post
    But we don't know yet what kind of role this pram is intended to fill.
    I guess that is a question to me? It is primarily a personal experiment in strake lofting theory. I am experimenting with the possibilities of achieving a well curved hull shape by using variable width strakes. Wide strakes on the bottom and sheerline, and progressively narrower strakes around the turn of the bilge. In principle this can achieve maximum "roundiness" with minimum cutting.

    (As to the function of the boat, it is a stable (can stand up) initial stability shape intended for flat water compact and car-toppable. Pond fishing, etc.. Roughly equal in function to a Bolger Tortoise.)

    Here is the strake layout lofted attempting to achieve balance and progressive strake widths.


  12. #12

    Default Re: New design, 6'10" lapstrake pram, "Lucky 13"

    No, No, No

    Enough of this stuff.

    Finish the Topaz Spyder FIRST or donate it to me .

    IBT

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