HDPE for bottom hull skin or line-x

Discussion in 'Multihulls' started by CerealPirate, Feb 26, 2021.

  1. CerealPirate
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    CerealPirate Junior Member

    Ok so the wheels have been turning and I am set on a Wharram/Waller/Woods cat around 30' my design would be solid hulls no through hulls ect. but I was wondering would it be possible to glue hdpe to the bottom kind of like 1/2 in or 3/4 thick ? or coat the hulls with line-x?

    the theory behind hdpe this would be a cleaner bottom and the main factor hdpe (black) is more durable in salt water and would in theory not require any drying out. only to fix or refit but not to paint ect.
    the same theory as above but using line-x to coat. both would add a layer of protection to the hulls. im not 100% about algae growth on line-x but again ... all theory. after seeing what the Indonesian people are doing with hdpe it kind of made sense. why are we using bottoms that break down and promote growth in sea water 0_o?? it makes sense to use the materials that are more resilient than those of yester years. dont get me wrong Glass has stood the test of time but with many many hours of cleaning and painting ect. however there is plastic bottles and even rubber ducks still floating the ocean after decades at sea ... with no scrubbing or bottom painting. now that is food for thought.

    Am I nuts or is there anything worth investigating here? I know making an outer hull out of hdpe will be a pain and probably cost more that 3 years of haul outs and paint but .... we are talking about decades of protection vs a year or two.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Why would you want 1/2 to 3/4 " added to the hull ? Or do you mean as the hull ? That would start to get terribly heavy, if the former. Obviously it isn't going to conform to any compound curvature, either. As for gluing, that seems to be what it isn't adaptable to, which might be related to its property of not holding marine growth.
     
  3. Barry
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    Barry Senior Member



    Or just build it out of hdpe
    Joints are heat welded
     
  4. gonzo
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    gonzo Senior Member

    You are making too many assumptions. The options on the survey reflects the bias. Try to order your thoughts by starting a Statement of Requirements (SOR). Also, if this is your design, post some of the specifications and the reason for them.
     
  5. CerealPirate
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    CerealPirate Junior Member

    added to the hull ... but your right that thickness would be way too heavy. and I just read about its issues bonding to other surfaces which brings up another issue. as for conforming heat would have to be applied. looks like its back to the drawing board. might be easier to head down the line-x route and start there.
     
  6. CerealPirate
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    CerealPirate Junior Member

    funny you posted them ... I actually contacted them and they told me a full HDPE sailboat wouldn't be sound in blue water. hence my idea of just lining the bottom hulls with it. all the strength of a regular boat with the ease of maintenance of a plastic. the idea is to get away from the circle jerk of haul out, scrape, paint and repeat. by testing new a new method we might just save thousands down the road.
     
  7. CerealPirate
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    CerealPirate Junior Member

    I only assume hdpe is better in salt water because of what I have read. So my starting point is a wooden glass wharram. the reason for trying a new hull covering/ outer skin is minimize if not eliminate future cost. Line-x is being used already on boats but I have yet to find any hard info on the life span in salt water. if you have any links about the longevity of Line-x in ocean applications please share. the money spent on just bottom work could be better used for other equipment in the long run. hence why I am opening this conversation about hdpe... in hopes that I can save not just myself but others money ... which is always a good thing ;)
     
  8. Rumars
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    Rumars Senior Member

    If it's just a liner as antifouling and a little bit of abrasion protection, why the big thickness? 1-3/32" is enough, bend by hand, weld the joints, screw or nail to the underside of the boat. Call it the evolution of copper plating to HDPE plating.
     
  9. ondarvr
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    ondarvr Senior Member

    You can buy sheets of HDPE with fiberglass cloth scrim embedded into the surface. This allows for very good bonding to a composite hull.

    And in thin sheets you can heat it to conform with simple shapes. The thinner the better.

    Delamination hasn't been a problem, but it wouldn't be easy to remove and replace sheets.
     
  10. gonzo
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    gonzo Senior Member

    More durable than what and why is drying out an issue?

    Your main problem is how to shape the polymer sheets to the bottom and how to attach it. Shaping with heat is not too difficult if you are good with your hands. Attaching it is a much larger can of worms. Screws or nails will go through the fiberglass laminate, let water through and cause delamination. You can prep the surface with coarse sandpaper, "activate" it with a torch and glue it with epoxy, but the adhesion is not great. I doubt you can save money from using antifouling. The reason bottoms get a lot of growth is that people spend years at a mooring or dock. If you sail more than stop, the bottom will stay clean.
     
  11. Barry
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    Barry Senior Member

    The days of scraping can be easily done away with. On our 40 power boat, we used Micron CSC, might have a new name now, made by Interlux.

    About every 3 years, we would haul it, had to for zincs anyway. As the bottom was non toxic, a pressure wash, about 1 - 2 hours, and the bottom was clean enough to repaint,

    I then just did a light hand scotch pad scuff, and applied 3 coats.

    This is an ablative paint. Meaning it sluffs/sloughs? off when the boat is moving. Our boat would sit for 6 months over winter in the ocean. It was furry when we went on our first trip, after half a day, it looked like
    new.
     
    Last edited: Feb 28, 2021
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  12. SlickMick
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    SlickMick New Member

    Long time lurker, finally have something to contribute:

    HDPE is a polyethylene plastic that is notorious for being resistant to adhesives. It is used as molds for epoxy resin. To get it to stick to your hull, you will need a very special primer. HDPE is very durable but will likely shear away over a relatively short period of time. It can be a good hull material, but not a good hull laminate material.

    Line-X is a company that specializes in polyurea coatings. The coating they are most known for, Line-x, is a polyurea elastomer. It is mostly used on decks or as a hull liner for freshwater boats. It does not do so well in saltwater or being submerged for a long time, as opposed to smaller freshwater boats that get hauled out after each use. Line-X is not a unique product. There are many polyurea vendors out there with many different formulations. Line-X has 20 themselves. Polyurea does cure very fast and is applied fast, making it a good business.

    Within the same family is also polyaspartic coatings. These can give the SAME qualities as polyurea coatings but can be rolled or sprayed on with normal equipment. Polyureas need very special equipment, which adds to the cost. Polyaspartics also come in more colors or even clear. What you want to do is shop around an find one that has the characteristics that you need:
    1) Bonding/adhesion - the best you can get
    2) Saltwater resistant (listed in chemical resistance), UV resistant, hydrolysis resistant (doesn't soak up water)
    3) Hardness - 78 minimum. This is inversly related to its elasticity
    4) They will all be elastic and you don't need much of it. If you hit something and your hull cracks, this stuff will stretch and not puncture, keeping water out and your hull from separating so much

    It all comes down to.... what are you trying to solve for? Bottom cleaning, durability, or the elastic safety measure? If its just the first two, what you should really look into is antifouling nanocoatings. I recommend Coval. Its tough, hydrophobic and marine life can't grow on it. It is not a UV blocker so you might need to protect whats under it by adding something or a primer. Bare wood needs a coat of epoxy before applying.
     
  13. rob denney
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    rob denney Senior Member

    Thanks Slick. Have you any information about how well the Coval works, it's application, cost or anything else that might be relevant?

    Thanks.
     

  14. SlickMick
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    SlickMick New Member

    If you have an inorganic hull, it will bond extremely well. It is considered semi permanent. What's great is it sticks to itself so you just scuff it up and bit and reapply. They claim it lasts up to 10 years. I've seen some demos where they blowtorch it and try scratching it with a coin. You can roll it on but HVLP works better for an even coating with no lines. They have a website: https://www.coval-group.com/marine

    You can coat your prop and hardware with it as well.
     
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