How To Choose Proper Fiberglass Weight

Discussion in 'Boatbuilding' started by DRD Boats, Jun 7, 2012.

  1. DRD Boats
    Joined: Mar 2012
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    Location: Wyoming

    DRD Boats Junior Member

    Hello I am looking into building a fiberglass drift boat. My question is how do I select fiberlgass weights for woven roving and chopstrand mat that will produce a strong but light weight hull? I would like to do a 6 layer layup alternating starting with chopped strand mat with roving over the top to get 6 layers, this will be for the bottom. For the gunnels im thinking 4 layer layup using the same combo. Will this be thick enough to run along rocky river bottoms of the west? I would like to achieve a gunnel thickness of about 1/2" and a bottom thickness of about an 1". I also would like to keep the hull weight around 300Lbs. Let me know what you guys think?
     
  2. idkfa
    Joined: Sep 2005
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    idkfa Senior Member

    What's the dimensions of the boat????

    btw, strong and light usually means cored, not solid glass, and not with brittle polyester resin.
     
  3. sabahcat
    Joined: Dec 2008
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    sabahcat Senior Member

    Thanks for the giggles :D
     
  4. DRD Boats
    Joined: Mar 2012
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    DRD Boats Junior Member

    These are the rough dimensions:
    Gunwales 17' 4"
    Centerline 15' 10"
    Beam 83"
    Oar Lock Height 25"
    Bottom Width 57"

    Google drift boats to get a feel of what the boat will look like. We are also considering vacuum bagging it.. Any thoughts on using this over a standard hand layup??
    Side Height 23"
     
  5. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Both the 1/2" and 1" dimensions are too thick, this would make the boat far heavier than 300 lbs. 1/4" and then 1/2" in the chine would be closer.

    Some designs allow the floor to flex, having it thick at the chine and thinner on the flat bottom, this way it slides over rocks rather easily. Others use a core on the bottom so it doesn't flex, this can help make it row easier.

    If you plan to use roving then 24oz is what you want, use 1.5 oz mat.
    Non woven fabrics (something like 1708) will give more strength for less weight though.

    Infusion works well, the finished product will normally be lighter and stronger, but you need to do some testing to get it right.
     
  6. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Considering the level of expertise you've shown here, I'd strongly recommend you get a professional to spec out a scantlings list and laminate schedule. It's obvious you need serious guidance from your questions or a better choice is to buy a set of plans, for a 'glass drift boat and adhere to the laminate schedule. Drift boat plans aren't expensive and the value of scantlings that not only work to suit the SOR, but also save you the builder, materials and layup effort can't be discounted.

    Simply put, no one can offer meaningful advise for your laminate schedule without a clue about the boat you're attempting to build. It's like asking what tires to put on a car, without knowing what make, model or year it is.

    Hire a pro or buy a set of plans, so the engineering details (like the laminate schedule) are already calculated for you.
     
  7. tunnels

    tunnels Previous Member

    You have a problem with using polyester resin ?? :?:Dont blame the material blame the person that using it if theres a problem !!
    Can make light and strong and just solid glass no core and use polyester resin !!!:confused:
     
  8. DRD Boats
    Joined: Mar 2012
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    DRD Boats Junior Member

    We have hired someone with insight.. I just would like to do as much research for myself so I can have educated discussions with our builders and know whats going on.
     
  9. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Most drift boats are over built, there isn't much engineering involved in laminate thickness.
     
  10. idkfa
    Joined: Sep 2005
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    Location: Windward islands, Caribbean

    idkfa Senior Member

    I've never built one but my guess would be ceder strip, 1/4 thickness, saves having a female mould, too. and then (up to)1/4 glass with epoxy either side. This way you've got tough skins that can take impact and still a somewhat flexiable hull. BUT..... I'm no expert so add salt!!!! 300lbs will take some engineering/numbers!

    ps. vinylester can be as good as epoxy. polyester is just crap! IMHO idkfa,
     

  11. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member


    Some use VE, some use polyester, they all hold up mainly because they're overbuilt. It's sort of a consumer driven thing, thicker means stronger and each guy thinks he will beat the boat to death pounding through rock strewn white water (very few do). So thicker chines means a better boat in their mind.

    Wood drift boats are for show, while they look great, the up keep and maintenance is too involved for the average guy. The boat is just a tool to get where the fish are, so any added work to keep it in shape is a negative.

    I used to build them and still supply most of the builders with resin and gel coat. Using VE and knitted fabrics my boats weighed around 200 lbs plus or minus depending on how they were set up.
     
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