Scantlings for welded HDPE boat construction

Discussion in 'Fiberglass and Composite Boat Building' started by Steve W, Jul 2, 2017.

  1. Silverbreeze
    Joined: Feb 2009
    Posts: 69
    Likes: 4, Points: 18, Legacy Rep: 13
    Location: Amsterdam

    Silverbreeze Bruno Tideman

    Black is no problem in Dubai where it is really hot, the HDPE does not warm up as much as aluminium does....
    only black is 100% UV resistant, other colours become brittle over time...
     
  2. fenfen
    Joined: Jul 2017
    Posts: 15
    Likes: 0, Points: 1
    Location: Oregon

    fenfen Junior Member

    After thinking it out alot, a aluminum frame built in longways with welded width wise cross braces, producing a lattace 16~"by 12~"(( area equal to a hdpe picking tank lattice super structure)) would be sufficient I belive!
    As to drap molding i believe having horizontal poles at each end of the hull with a 3 inch space bettween em and the hull, will get the draping not to fold on itself in the middle. Then taking a large hinged clamp if you will closing it over the ends of the boat to pintch them together. This clamp being in consert with the bow/transom profiles((planning a double sided boat anyhow)). Also cutting the excess.
    Further more canvas is stretched tight to the framw work before hand, letting only small depressions bettween lattace works. Subsequently the another is tossed upon the out side of the drapped hdpe tobe pulled taunt quickly to perform a Good molding, this canvas is removed after cooling, the inner "Sandwich" is permanent...
    Later after cooling...
    With the bow clamps removed the profile extrema is shaved to a consistent curve. There upon a aluminum flat bar is shapped to fit, lagbolted inplace with a hdpe backing that is air heat welded to the bow extrma making a water tight seal and adding extra collision protections.

    The new skin is now bolted to the inner frame work via a sytem of L brackets lagged to thick blocks of hdpe indaviially plained to flush against the hull and heat welded to it, encapsulateing the lags.

    The deck is simply cut flush/flat and a deck of hdpe is heat welded to the hull.

    In the end making a one piece hdpe hull and deck. No joints, rivets, seams.
     
  3. fenfen
    Joined: Jul 2017
    Posts: 15
    Likes: 0, Points: 1
    Location: Oregon

    fenfen Junior Member

    I think my only concern is viability as too other methods, as these are alot of steps with alot of work such as L bracket placement would be as tedious as lap strake beveling for a plank boat.
    Secondly only time would tell of if flexing would rub thru one spot of another after years, as hdpe plastic is very soft to metal!

    Lastly i did calculate a therotical boat, w/o a deck, 30' by 6.5'. Such would have approximately 500lbs of hdpe at 3/4" inch thickness. Idk what plywood would be, or solid wood. Is this heavy?
     
  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Seeing you are going to do some welding, why not weld the whole shebang ? I don't entirely follow what you are planning with the draping, but I think it is going to be near impossible to get a shape that doesn't sag between the framing. I think you need a continuous surface, not frames.
     
  5. Silverbreeze
    Joined: Feb 2009
    Posts: 69
    Likes: 4, Points: 18, Legacy Rep: 13
    Location: Amsterdam

    Silverbreeze Bruno Tideman

    Sorry guys, I have lost teh way you think. We make our boats from sheet material welded together only.
     
  6. Silverbreeze
    Joined: Feb 2009
    Posts: 69
    Likes: 4, Points: 18, Legacy Rep: 13
    Location: Amsterdam

    Silverbreeze Bruno Tideman

  7. Bala5278
    Joined: Feb 2018
    Posts: 20
    Likes: 0, Points: 1
    Location: Pondicherry

    Bala5278 Junior Member

    Hi Mr Bruno, Would like to know how you weld the under deck of the floor since you can weld only on the top once you place it. Any other way to solve this issue?
     
  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    You might ask the same question about welding under any kind of floor, when there is no longer access to the underside.
     
  9. Bala5278
    Joined: Feb 2018
    Posts: 20
    Likes: 0, Points: 1
    Location: Pondicherry

    Bala5278 Junior Member

    Hi Mr Efficiency, Yes that's true , but would like to know how we could solve that issue particularly with HDPE (since it doesn't fuse as good as the metal). Any alternative idea?
     
  10. Silverbreeze
    Joined: Feb 2009
    Posts: 69
    Likes: 4, Points: 18, Legacy Rep: 13
    Location: Amsterdam

    Silverbreeze Bruno Tideman

    We close the deck before we adding the buoyancy PE balls, using slot welds on the scantlings with a strip on top. It took is some time to develop but now all sides of the boxes are completely welded and that makes a rigid honeycomb like construction.
     
  11. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I know not a great deal about the material and its methods, but is seems to have some appeal, the idea it needs to be black, to withstand UV, seems a limiting factor.
     
  12. Bala5278
    Joined: Feb 2018
    Posts: 20
    Likes: 0, Points: 1
    Location: Pondicherry

    Bala5278 Junior Member

    does a 20 mm HDPE panel bends , for the hull shape? any low heating required?
     
  13. starbright
    Joined: Mar 2019
    Posts: 1
    Likes: 0, Points: 1
    Location: California

    starbright New Member


  14. emre istutan sectorboat
    Joined: Sep 2019
    Posts: 1
    Likes: 0, Points: 1
    Location: istanbul

    emre istutan sectorboat New Member

    It is a colorful (grey-black and yellow) boat made entirely (hull-deck-SS and interior) of HDPE and I designed and manufactured for my customer.
    Your information.

    Emre
     

    Attached Files:

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.