Inflatable PVC boat as mold to creat a protective fiberglass Hull

Discussion in 'Fiberglass and Composite Boat Building' started by Bzidro, Apr 1, 2019.

  1. Bzidro
    Joined: Apr 2019
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    Location: Portugal

    Bzidro Junior Member

    I have an inflatable pvc with 3.60 metter (12 feet) and most of my navigation is done in rivers, reservoirs and lakes and I often encounter many floating debris from trees. I have a similar idea https://www.boatdesign.net/threads/using-an-inflatable-pvc-boat-as-a-mold-to-lay-up-fiberglass.59493, and want to use the same process, which is to make a fiberglass hull only up to 3 quarters the height of the floats with holes to pass fixing straps, so that I can sail without the risk of drilling, and even dock on the banks with vegetation that could easily pierce.

    Find it a feasible idea, using first adhesive film and then several layers of newsprint and wood glue to protect the pvc from epoxy ???
    My boat is almost flat bottom with a sligth inflatable keel.
    The Main motivation is both the low cost of all this and the very high price of a rigid boat with a similar size, otherwise would have bought a rigid initially.
    Thank you !
    Bzidro.
     
  2. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member


    So you’re talking about building a fiberglass guard to fit over your RIB?
    If indeed you do find a way to do a decent job of it, you will only have a much heavier RIB, with a weak brittle shell, that costs as much as a fiberglass boat.
     
  3. Bzidro
    Joined: Apr 2019
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    Location: Portugal

    Bzidro Junior Member

    Hi kapnD !

    I have carefully read your entire interpretation of what I have described, and in fact there is a lack of information about what I intend to do and how to do it, and the very behavior of my Inflatable that is Not Semi-Rigid, RIB, but has a full interior bottom of plywood and when the keel is inflated becomes completely rigid from the outside.
    I'll try to send a photo of boat and even a sketch of what I intend to do. Thanks for the help.
     
  4. Bzidro
    Joined: Apr 2019
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    Location: Portugal

    Bzidro Junior Member

    kapnD
    I do not know how much a new fiber boat about 14 feet costs in USA, but do you know or imagine how much can it cost here and How much is the average salary in Portugal ???
    I tell you both: 993,75 United States Dollar is the Average salary, 887 € !
    A new fiber boat about the same 14 feet, costs never less than 4 481,22 United States Dollar, 4000 € !!!
    Do you realy think I'd spend the same money building the fibre hull ???
    This inflatable of mine , costed 520 € - 582,57 United States Dollar
    Inflatable boat OZEAM model 360 of 3.60 meters Inflatable boat OZEAM model 360 of 3.60 meters https://www.thenauticstore.com/en/inflatable-boats/99-ozeam-360-inflatable-boat.html

    Greetings all.
     
  5. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    You missed the most important statistics.
    How much is the Fibreglass Resin and Cloth going to cost you ?
    To do that, you will need to specify what amount of materials you expect to use.
     
    Bzidro likes this.
  6. Bzidro
    Joined: Apr 2019
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    Location: Portugal

    Bzidro Junior Member

    2 layers of fiberglass blanket of 450 gr / m2, for 5,50 € m2, equals to 82.60 € or 92.55 United States Dollar, 15 m2.

    18 kg of epoxy resin SR 1500 at 27.67 € per kg equals to 498,06 € or 558,47 United States Dollar.

    http://www.sicomin.com/datasheets/product-pdf39.pdf Product Datasheet

    Do you think it's enough for the purpose or need one more layer ?
    Very very far from the 4000 € of a fibre boat...

    Greetings all.
     
  7. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Still lacking lots of information, thought you were going to fill us in on details and photos?
    BTW, money doesn’t just grow on trees in the USA, either.
    Grandpa used to say, “Don’t start vast projects with half-vast ideas!”
     

  8. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Next round of questions :
    Are you going to leave the RIB inflated for strength ?

    Next - the area to fibreglass is going to have to extend up the sides in order to stay on, and resist getting torn off at impact or cracked from the flexing of the RIB Hull, and also to account for curves in the hull and wastage. So I think that the area to cover should be more like 9 m2.

    I think the F'glass you are quoting is chopped strand matt. You need woven, bi-axial say around 340 gm/m2 to cope with the flex of an inflated hull AS WELL. That will probably be another say $12 per metre. 9m * $5* $5 * $12. So lets say $200.

    Next, the total weight of the Fibreglass will be about
    450 + 450 + 340 grams per M2 (1240 gms per M2)
    1.25 kilos per M2 * 9
    say 12 kilos.

    So, you will need at least 12 kilos of Epoxy if you get a good 50/50 wetout , probably more like 15 including wastage, sanding and imperfect wetout.
    You also need matching hardener. They dont always quote that in the price.
    I can get cheaper Epoxy at $100 per 4 litres, and .8 litres of hardener at $40 per litre. ($140 per litre)
    So, 15 litres total, / 4 x 4 litre kits, say around $600.

    Now, you need to paint the Epoxy, because it will degrade in UV. You can either go cheapo house paint and waterproof undercoat, or quality 2 part paint. Let's assume cheap $200

    Consumables like "sandpaper", Brushes and rollers, Acetone cleaner, gloves and face masks, mixing cups and measures, let's say another $200

    Plus the RIB $600

    You may be looking at around $1,800

    ... For a craft that is overweight, still relies on air inflation, with a cheap paint job that will need redoing every year, that will collects sand and rubbish between the two hulls to puncture the inflatables one, that you cannot ever sell to anyone and maybe not even repair if you cant get the fibreglass shell off..

    You also run the risk of damaging the fabric of the RIB while you coat it, either with cured pointy fibreglass "needles" as you sand, chemical attack or some accident, plus you have all the manufacturing risks like badly mixed epoxy etc, and all the effort of actually building it.


    You would probably be better off just building a plywood stitch and glue dinghy, with glass epoxy covering from a plan.
    Say 4 sheets of ply at $120, 6 litres of Epoxy, and just FG Tape at the edges
    If you take some care, you will end up with a product that is insurable, re-sellable, light and reliable for 2/3rd cost of the proposed RIB enhancement project.
    Flat Skiff 12 (FL12) - Study Plans https://bateau.com/studyplans/FL12_study.php?prod=FL12
    Dinghy.jpg
     
    bajansailor likes this.
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