PE as material for boat?

Discussion in 'Materials' started by Hornblower, Sep 10, 2011.

  1. Hornblower
    Joined: Sep 2011
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    Hornblower Junior Member

    Hey,

    I used to hire houseboats made of steel on british canals ("Narrowboats"). As they are very solid you don´t have to worry at all if you hit the ground or the edge of a lock. One day I would like to own one for myself and it might be like those Narrowboats in GB. But there´s one disadvantage: they are much to heavy for beeing trailed by car when I want to discover other waterways.
    So I searched for another material that ist as insensitiv as steel but not as heavy as steel. GRP has the risk of osmosis if the gelcoat is scratched, so it doesn´t fit. A small, open floodboat I know ist made from PE (exact PEHD). That is light and very solid. As I found out about PE it needs a special treatment for beeing resistant against UV and you can hardly glue it (must be welded).
    But I found no boats made of PE in the size of let´s say 12m.

    Can anyone tell me something about PE and the use for boats?


    Cheers

    Hb
     
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  2. pistnbroke
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    pistnbroke I try

    look at polycraft in australia I think its www.polycraft.com.au there are only three makers as I understand it in the world and www.fun-yak.fr is the other along with trident in the us......Very unusual stuff to work with and fit out with normal boatie bits ...nothing as in nothing sticks to it ..welding is not a problem but you end up putting in course threaded bolts ....if the original design is bad ..that will be fun yak its a real pain ..I have one
     
  3. Olav
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    Olav naval architect

    PE isn't a very good material for boatbuilding. It is neither very strong (yield strength is ~ 30 MPa) nor very stiff (modulus of elasticity ~ 1.3 GPa). It only has its merits when used in a building method called "roto-moulding":

    PE pellets are inserted into a closed (aluminium) mould which then is put into an oven where the PE will melt. A very sophisticated rotation programm ensures that the liqiud PE will spread all over the mould; even different wall thicknesses are possible.

    The result is a very low-cost building process (provided there's a certain lot size), but the boat will be quite heavy compared to FRP or wooden hulls as it takes rather large thicknesses to overcome the aforementioned lack of strength and stiffness of the material, it's also less scratch-resistant and difficult to keep clean as it is prone to electrostatic charging.

    I have no idea about the maximum size of boats build this way, but in general I think it lends itself more to small craft.

    Check out this video about roto-moulding at Pioner Boats in Norway. There are also other yards in the UK that build small dinghies using roto-moulded PE.
     
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  4. PAR
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    PAR Yacht Designer/Builder

    Olav has pinned down high density polyurethane and other then roto or other molded, small boats, it has little use as a building material.

    Your impressions about GRP are less an issue with modern resins, particularly vinylester and certainly epoxy. For you application, you don't need the modulus (or expense) of epoxy, but a good polyester or vinylester will do just fine. Bottom protection in the form of runners (HDPE?) can stave off most of your concerns in shoal tidal areas.
     
  5. pistnbroke
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    pistnbroke I try

    Ok it must have some addvantages or I would not have bought it
    1/ indestructable ..leave it outside in the sun /rain no deterioration. So holds value well.
    2/ leave it in the river and it wont fill with water because you can leave the bungs out and the water runs away ( double skin hull )
    3/ Cheap at £1300 I thought for a 3.7m boat.

    Would I buy another ..yes...but make sure everything I wanted was moulded in and all I had to do was put seat cushions in it

    Biggest problem Fun Yak the makers briliant rotomoulders very inventive but boat design 4/10 ..quirky french ..they dont even know the outboard operator sits on the starboard side ..just look at the web site !!! www.fun-yak.fr
     
  6. michael pierzga
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    michael pierzga Senior Member

  7. Hornblower
    Joined: Sep 2011
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    Hornblower Junior Member

    Hey,

    thanks to everyone for the infos.

    The small boats you were talking about are not made like I ment.

    The hightide rescueboat I wrote about at the beginning was not made with roto-moulding. It´s made from solid HDPE plates, thickness about 1cm or more, welded together. They are really stiff. Look here: http://www.teuto-kunststofftechnik.de/hochwasserboote.html

    The basic form of my boat would be similar: Plates welded together (the German word would be "Knickspant", maybe with flat bottom) What do you think?

    Cheers.

    Hb
     
  8. michael pierzga
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    michael pierzga Senior Member

    Interesting...first time Ive seen it.
     
  9. PAR
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    PAR Yacht Designer/Builder

    HDPE is not the best choice for building a hull shell. It has some advantages, but also has several distinct disadvantages, weight being a difficult one to over come.
     
  10. alan white
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    alan white Senior Member

    What about actual boats that have been built, which have lasted well? Best to follow advice here that HDPE hasn't yet worked as a boat construction material (except for canoes, kayaks, etc.). To work out the weight issue, see how poly canoes, e.g. weigh more than wood, fiberglass, or even aluminum.
    Beware claims by re-inventors of the wheel who have a vested interest in promoting a new construction method for boat hulls. It's typical to downplay or dismiss fatal flaws of a particular material application because one is trying to sell an idea. However, many people get sucked in by promoters of new ways of doing things, ways that are often short-sighted.
    The best advice is probably to do what you're already doing. Where youi find disagreement amongst experts, err on the side of the majority and throw out the opinions that differ the most from the common state of the art.
     
  11. pistnbroke
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    pistnbroke I try

    I understand some rotomoulded boats are still in use afte 40 years ..they are certainly the choice for hire fleets in Australia where aluminium was the previous choice as well as for rescue vessels ...The port of london authourity has 30 12 ft Fun-yaks and the french Sapier Pompier hundreds ...love them or hate them its one of those situations.
     
  12. thudpucker
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    thudpucker Senior Member

    I doubt if HDPE would be much of a boat. BUT...it makes a heckuva lot of usable containers. I made all kinds of stuff for my barn out of it.
    I NEVER found a Glue that worked well though. I had to double the layers to make a strong connection, but it held that way.
    I made Console covers for my little boats as well. It's so plentiful, it seems like a waste to throw it all on the Dump.

    Michael P, thanks for that link to Metzler. I had one of their boats and loved it.
     
  13. pistnbroke
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    pistnbroke I try

    its all a question of what you call a boat and what you want to do with it .....
     

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  14. PAR
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    PAR Yacht Designer/Builder

    Those girls look to have had HDPE injections or implants . . .
     

  15. pistnbroke
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    pistnbroke I try

    Naah mate thats australia your eyes are out on storks 24/7/365
     
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