HDPE pipe for simple raft.

Discussion in 'Boat Design' started by china, Jan 4, 2014.

  1. china
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    china Junior Member

    Hi, just to explain I am planning to make a modular raft system that ties together.

    The system will consist of four 4' x 8' rafts with 10 inch HDPE pipe running 8' on each raft both sides.

    If I could ask a question please.

    I have read that 10" PVC pipe has a buoyancy of 34lbs per foot. With HDPE pipe being lighter as well as stronger, can anybody confirm if it will more buoyant and if so, by how much more?

    Any advice would be great. Thank you.
     
  2. Skyak
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    Skyak Senior Member

    Archimedes' principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.

    Assuming no difference in deflection or size the difference would equal the weight difference between the tubes.
     
  3. china
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    china Junior Member

    That's a fascinating fact.

    Thank you, very helpful.
     
  4. portacruise
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    portacruise Senior Member

    There might be a "concealed" size difference because the wall thickness might not be identical for the two different types of pipe. Would it have much of an effect though?

    Porta
     
  5. Barry
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    Barry Senior Member

    10 inch hdpe or pvc pipe has an od of 10.75 inches which gives it a buoyancy of 39 pounds per lineal foot less the weight per foot of the material
    pvc and hdpe come in various wall thickness depending on the schedule or pressure rating

    Sched 40 pvc weights 7.6 pounds per lineal foot so it will provide 39 pounds/foot less 7.6 pounds/foot or 31.4 pounds per lineal foot.

    110 psi hdpe pipe, one company anyway, has a weight per foot of 9.6 pounds so it would provide 29.4 pounds per lineal foot of buoyancy

    These numbers are approx. and of course dependent of the wall thickness of pipes.

    Sched 40 is a standard pvc pipe wall thickness though perhaps there might be a sched 20.
    Hdpe, might be available in even less wall thickness than the one for 110 psi.
     
    Last edited: Jan 4, 2014
  6. gonzo
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    gonzo Senior Member

    That assumes a fully submerged pipe. The rule of thumb is about 50% submersion.
     
  7. china
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    china Junior Member

    Thank you all.

    Some good information has been posted.

    I will research my floatation some more. My pipes will have a 7.6mm wall thickness.

    The 4 separate 4' x 8' rafts connect together making a 8' x 16' gypsy bowtop caravan that floats. The first section can be disconnected and used as a small tender to get to shore with a small electric motor and also be used to tow the other sections in line at 4' wide to be connected together someplace else.

    Useful for narrow canals where I plan to build it in Kerala, South India.

    Thanks.
     
  8. rwatson
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    rwatson Senior Member

    There have been so many posts of plastic tube rafts on this forum over the years.

    It might be a good idea to look them up to see why the material and method are such a bad design choice.
     
  9. portacruise
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    portacruise Senior Member

    If you haven't considered it already, do you have rugged bamboo in large diameter which is suitable for making boats?

    http://www.boatsandrice.com/bambooRaft.html

    Cheaper, lighter, will not sink if punctured, gives rather than breaks upon impact, etc..

    Porta

     

  10. china
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    china Junior Member

    Thanks. I will ponder on that. Thanks for bringing it up.

    I know plastic pipe isn't the best way to float a vessel. I was going to arrive somewere and wanted to get a simple raft in the water in around 1 week. I thought the compromise of heavier materials and quickness of the project might outweigh the fact it isn't the best material to use.

    Thank you to all for letting me pose this question, this thread has helped me rethink and change my mind.

    It has been a big help. Thanks.
     
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