Making a hull

Discussion in 'Multihulls' started by Fanie, Feb 26, 2012.

  1. Fanie
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    Fanie Fanie

    Getting the form for a hull is always the most difficult part. As many home build okes discover, the easy part is drawing it on the computer using a design program, which is fine, you have to do that.

    The next challange is getting the sctual shape so you can glass the thing to become a boat. There are many things involved, the amount of glass and resin, bulkheads and all the nice things.

    I'm just going to show how easy it is to make a shape for a boat that you can glass over, this is just one of probably many methods you can use. You can after this fair it, or even make a mold for more of the same.

    I use a round tube of pipe, the bigger and heavier the hull, the bigger the pipe diameter has to be. You don't want the pipe to bend or it will come out as a banana boat.

    Metal tubing has a way of bending very nice if it is bent to a form. You can also change the bending more or less, so if you want an even curve it can be achieved and manipulated very easily.

    The principle of getting the shape is spacing pieces of tubing around the pipe to make a form if you would wrap it. The pictures will indicate what I have made before and it worked quite well.
     

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  2. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    This is a very intriguing idea. Set that rotating and you could wind it with shrink wrap from stem to stern and just glass over it the way you did the glass cross-beams. I like it. :)

    Must spread rep first. :(
     
  3. Fanie
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    Fanie Fanie

    In the above you can see how easy and well the tubing shapes. The spacers between the tubing and the pipe is what gives the form and shape. You can make almost any shape in this way.

    Second step would be to cover the spaces between the tubing to something a bit more rigit where you can glass over, I use plastic to wrap the shape.

    The next would be to glass the shape. I would suggest you pre-wet the glass then lay it over the plastic and lightly roll with a roller to bond with the new and the previous layers.

    You have a choice here. You can glass to thickness and that would be the hull, or you can lay down some layers to make the form rigit, use putty or other filler materials to enhance the shape if you want and then wrap with plastic again before you glass the final shape.

    Once cured you cut the plastic that is exposed and the hull can be removed form the shape.

    Some tips -
    Pre-cut all glass once you know how and where you want to apply.
    To pre-wet glass you can use a table with a sheet of prolyprop to work on.
    Use a rubber roller to squish excess resin out of the fiberglass, it comes out a lot lighter.
    Two persons lift the wetted glass and place where it has to be.
    Make the hull in one go, or the old and new may delaminate.
    Mix only enough resin at a time you can use up before it will cure.
    Last layer up should be peel ply - it makes fairing a LOT easier.
    Allow enough time to cure properly
    Preparation is key, once you started there is no time.

    Good luck :D
     

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  4. Fanie
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    Fanie Fanie

    Hi Hoyte,

    There is actually so much one can do to achieve different results. I haven't tried it yet but you can probably just cover the frame with a thin ply wood rivited in place as well to enhance the curvatures, wrap with plastic and then glass over that.

    I don't like wood in the boat so I'm all fiberglass.

    Just to say something about the seeming complicated 'arms' between the pipe and the tubing - the jig I made is foldable, you can make your's arms permanent. The setup for mine is for another process, so just ignore that.

    You need end supports that can lock the rotation and if the supports are under the pipe you can add a transom or stern or whatever before you start glassing.

    The method is nice if you build a multihull, once the one hull comes off you can just wrap plastic and layer the next hull up.
     
  5. Fanie
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    Fanie Fanie

    To make a snug fitting deck you can, when the hull is done and cured some, wrap as is again with plastic, then glass the deck. It cannot but fit properly.

    You would then pull the deck, and then the hull once cured.
     
  6. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    I only plan a one off but it is 2 hulls identical. I think your system will work for me even if I build the er--- rotisserie from wood instead of metal. What is your opinion?
     
  7. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    I do plan to shrink the plastic wrap onto the wood jig.
     
  8. Fanie
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    Fanie Fanie

    Hi Hoyte,

    If you can make it out of wood it's also fine, I'm not good with wood so I prefer metal. Wood is also expensive here and not suitable for my process.

    I also think iron can be easily modified, you can make changes simply by cutting and welding, screws or rivits. Since it's a frame, it should also be lighter.

    Rotating the wood would work if you use a pipe (or axle) through the center. A gwala (don't know what you call them over there) also makes a thin strong axle and they have 8 sides that can be used with a laser cut handle for rotating.

    The whole shaped thing just have to be sturdy and rigit enough not to flex or deform when you rotate it. Iron makes it easy, not so sure about wood.

    How big is your boat ?
     
  9. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    It will be about 3 meters long and less than 2 meters wide assembled at launch. transoms about half a meter. Each hull will be a about half a meter wide.

    I looked for "gwala" but could not find it. Got a picture of one?
     
  10. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    The building frame I can assemble will not deform when it is werfeled.
     
  11. Fanie
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    Fanie Fanie

    Gwala attached ;) It's used for breaking the gravel during digging holes.

    What's with you and Manie and the bath tubs :D
     

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  12. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    Thanks for the photo. Those are called digging bars here. This is a 2 hull project. Your folding cat is my inspiration which I call the Fishy Boxier Cat. There is a large area between the 2 hulls. Less like a bathtub and more like 2 wallpapering troughs linked together.

    Basic shape still undergoing modification:

    [​IMG]
     
  13. Fanie
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    Fanie Fanie

    What's the double tub :D used for ?

    They sell them gwala's at hardware shops, made from spring steel and they are fairly tough.
    What do you call them ?
     
  14. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    We call them digging bars. The double tub :D is so it will be stable even though short when powered with an outboard motor. I will also try to build a mast and lee board sailing rig for the boat. Its just for puttering around whenever camping near water.
     

  15. Fanie
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    Fanie Fanie

    Why so short ? Go at least 6m long... and wider is nicer. 3m long is going to pich like hell in any kind of mild swell especially with that shape bow, not to mention the slap and spray...., if you shape the hul to displace, it will make a big difference too.

    Also, the shorter a boat the more critical weight distribution gets. If you tiller steer the boat you and the motor will sit in the back, the bow is going to point at the moon when it's 45deg up :D

    Bigger is better, if you didn't believe Godzilla, ask the wife :D
    You know she may not be always right, but at least she's never wrong ;)
     
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