hdpe drape molding/thermoforming a hull

Discussion in 'Fiberglass and Composite Boat Building' started by fenfen, Jul 18, 2017.

Tags:
  1. fenfen
    Joined: Jul 2017
    Posts: 15
    Likes: 0, Points: 1
    Location: Oregon

    fenfen Junior Member

    I am planning a 28foot shunt style boat. My insane idea is to fusion weld four sheets of 1/2"x4'x16" hdpe. Then i Will build a oven from sheet steel+2x6s, using a shop propane heater some and ductwork.
    I need the hdpe at 380F.
    Then finnally i'll belly dump the whole giant sheet over a upside down boat skeleton. With some help throw sand filled lenghts of fabric to get it to confrom. Now the tricky part, i need your guy's help, if i fold and pinch the ends together with two boards + clamps i can form around a raked bow. Would that work with out folds? In my mind's eye yes but i maybe insane.
     
  2. fenfen
    Joined: Jul 2017
    Posts: 15
    Likes: 0, Points: 1
    Location: Oregon

    fenfen Junior Member

    Last edited: Jul 18, 2017
  3. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,026, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I'd suggest you start with a 1 : 10 scale model. You will only need a minimal amount of material, and might get a better appreciation of the difficulties you face. Sounds hugely problematic.
     
  4. fenfen
    Joined: Jul 2017
    Posts: 15
    Likes: 0, Points: 1
    Location: Oregon

    fenfen Junior Member

    Yeah idk. It's all possible, feasible. It's the unforseen that's the real issue. So if you all could lend your builder's minds, thanks.
     
  5. Smyrna
    Joined: Jul 2017
    Posts: 2
    Likes: 0, Points: 1
    Location: Turkey

    Smyrna New Member

    it is very hard for HDPE. I think that technique could not be successful for HDPE as acrilic forming, you should heat hdpe sheets at least until glass transition temperature (approx 130C) otherwise hdpe will want to turn back its old shape, over 125-130 Celcius it could be deformed and you may have bad surfaces and nonuniform thicknesses. So working with small experimental part will be better idea as Mr. Efficiency said. Relatively thinner sheets less then 8mm could be more successful I guess . 4 edges of the sheet may need to be tightly fixed on the mold before heating . I wonder the results of this experiment.
     
  6. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,026, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I really don't want shares is a project that attempts to create a hull shell, by draping a hot sheet of plastic over a former. This sounds like a process that might work with hideously expensive tooling, not a backyard undertaking.
     
    BrissoDamo likes this.
  7. fenfen
    Joined: Jul 2017
    Posts: 15
    Likes: 0, Points: 1
    Location: Oregon

    fenfen Junior Member

    My concern is modeling a hull shape with out concaves. Too not have folding for instance.
    2nd I've settled on a less than dream boat sozed beam of 5feet like a big canoe! Proa style.
    3nd a typo i mean big 16 feet by 4 feet sheets.

    Well initially it'd be just my self then for the actual forming i figure 10-20 people for an hour or two. I'd need that many to help quikly drape fabric sheets,tensioned with sand pockets and or a web of straps. Indeed I plan on forking over some exorbent amount to the local boat building club on the docks. They got space.
    I'm also contemplating a heaver clinker/chined design, as overlaping and fushion welding one bit at a time would be easy just alot longer build time.
     
  8. fenfen
    Joined: Jul 2017
    Posts: 15
    Likes: 0, Points: 1
    Location: Oregon

    fenfen Junior Member

    The hull shape is my question really.
     
  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,026, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    All I see in this, is a gnashing of teeth, and wringing of hands. To get a flat sheet of any material, to conform to an irregular, non-developable shape, requires stretching, and that stretching needs to be under tight control. As in a massive press. But, to convince yourself, try an experiment on a greatly scaled down size . If it doesn't work with that, it is no hope full-size.
     
  10. srimes
    Joined: Sep 2008
    Posts: 283
    Likes: 29, Points: 28, Legacy Rep: 214
    Location: Oregon

    srimes Senior Member

    Seems like you'd want a 2-sided mold to have good control.
     

  11. gonzo
    Joined: Aug 2002
    Posts: 15,513
    Likes: 1,049, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    I think the only way to get good quality and control the shape is with injection molding.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.