My current Project-Pontoon Junk Raft.

Discussion in 'Boatbuilding' started by djwkd, Jan 27, 2009.

  1. apex1

    apex1 Guest

    Ahhh.....re we happy to use metric system...:D
     
  2. robherc
    Joined: Dec 2008
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    robherc Designer/Hobbyist

    36"x8"x8" = 2304in^3

    2304/1728 = 1.333ft^3

    1.333x62 = 82.667lbs displacement per pontoon... Are you a good swimmer?

    To put it in perspective, 4 pontoons of that size would displace 330.667lbs while glueing 36 used milk jugs (5.5"x5.5"x10" each... but not all of that is buoyancy) to the bottom of your 3'x3' piece of ply (they'll fit..you MIGHT even be able to sqeeze 49 in there) would give you 324lbs of displacement (49 would give 441lbs displ.). Honestly, I'd go with the milk jugs for this raft...they're free and require less work to assemble...just smear glue on the bottom of the board (epoxy, polyester, or vinyl-ester will do), set the milk jugs on, and voila, raft (check out the "Free boat plans" thread for a cool "milk jug battleship").
     
  3. djwkd
    Joined: Jul 2006
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    djwkd Senior Member

    Right.I'll use the Two Bottoms of the first pontoons as sides for another..I'll have to plank out the bottom...
    You got the same thing as me, but i thought that that was impossible to have such a reduction in Displacement.
    So i'll have to plank out the bottom of the pontoons.

    Thanks, Dominic.
     
  4. robherc
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    robherc Designer/Hobbyist

    N.P....good luck
     
  5. djwkd
    Joined: Jul 2006
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    djwkd Senior Member

    New Design

    OK, so in the back yard i have an old cane shelf that is pretty big. What im thinking of doing is covering it with tarp and filling it with floatation. Then, n the top i will add a wooden deck. Doing this gives me 944lbs buoyancy without factoring in the weight of the bottles, or between 609lbs and 761lbs with factoring in the weight of them (between 40lbs - 50lbs per sqr foot), which is more than my previous idea.

    Here is a pic of the thing i found a while back and left in my back yard, knowing it would come in handy for some project to do with boats.
    [​IMG]
     
  6. djwkd
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    djwkd Senior Member

  7. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Ummm - how can I put this nicely, do you enjoy very cold water ?

    Try a slightly different approach for safetys sake. Rather than fill the frame up with junk that will cause problems and be hard to control, get some sticks or bamboo about the same dimensions as the larger bits of wood in the garden frame, and fasten them across the 'bottom' of the U shape like a floor. ( use wire, nylone ties, clothesline string etc. to secure them in place)

    Then run down to the local fabric shop, and buy enough cheap cotton fabric (thick and strong as you can afford), and cover the bottom and sides (on the outside) with the fabric, and stitch it tightly to the upper edges. You should have a quite taut covering all over the bottom and sides.

    Finally, scam some housepaint (not water based) from your neighbours and paint it all over on the outside with as many coats as you can.

    Tada - one lightweight, fairly usable Coracle (look it up on the net).

    If money is really tight, you can cover the frame and floor on the outside with Papier mache. (newspaper and wallpaper glue) to about 1/4" thick. Paint that thoroughly.

    The advantage of a hollow boat is - you can sit in it, less likely to tip over, and if it leaks, you will see the water coming in before you lose enough floatation to be dangerous.
     

  8. djwkd
    Joined: Jul 2006
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    djwkd Senior Member

    The advantage of a raft, however, is that if the water comes in, it doesnt matter because the floatation that is there keeps it afloat. Also, i only have to buy tarpaulin. I already have everything else. What i'm building here is on about a £10GBP budget. One day, all the 'traditionalist' mariners will start noticing that rafts are the way foward for budget 'boats'.
    If it gets a hole in, all this thing needs is a patch of tarp getting stitched on.

    On your (particularly valid) point of it tipping over, i have pondered fitting an outrigger type thing with stuff i have lying about the yard.
     
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