fiberglass help

Discussion in 'Boat Design' started by demoman, Mar 12, 2012.

  1. demoman
    Joined: Mar 2012
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    demoman New Member

    I am planning on undertaking my first hand laid fiberglass hull for a small jon/skiff type fiberglass boat with a max 20 hp outboard. i have the mold completed and am ready to start final sanding and polishing for the fiberglass. How many layers and what type of cloth should I use for the strongest hull conditions? I am planning on a polyester resin, but really have not much info on how many layers of lamination i need.
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    It depends on the laminate type, cloth or mat types, core if any, structural stiffeners and panel shape.
     
  3. demoman
    Joined: Mar 2012
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    demoman New Member

    Gonzo

    Thanks for the reply. I am planning on a good coat of gel coat and then layers of chopped strand mat (probably 2 0z ) and polyester resin for the laminations. Unless someone thinks that cloth or woven roving would be stronger, or more efficient. I am planning on individual horizontal fiberglass stringers, and 3-4" thick coast guard approved floatation foam for the entire bottom of the hull, and then a glassed floor. Very similar to the carolina skiff jon boat construction. Any thoughts would be appreciated.
    Demoman
     
  4. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    Demon,

    The designer of the boat is the one who should spec out the laminate schedule, if you are the designer then it's really your job to know how strong things need to be, and deciding how much glass goes where. Personally I think CSM is just this side of worthless since it is very weak, heavy, and accelerates water absorption into the skin, but as the designer it's your call.
     
  5. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Take boat length and divide by 1000. That gives a conservative thickness for a 20hp skiff. 1/8 " minimum.

    Buy "The Elements of Boat Strength" by Gerr. It will get you going along the right track in terms of how things are sized relative to one another. Scantlings, etc.
     
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  6. Ike
    Joined: Apr 2006
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    Ike Senior Member

    There is no such thing. The USCG does not approve flotation foam. Approval applies to certain items you must carry on board a boat. This includes things such as Fire Extinguishers, Personal Flotation Devices, and visual distress signals. Also some courses and schools for professional mariners are Coast Guard Approved. Flotation foam is not. Any one telling you they are selling Coast Guard approved flotation foam is violating the law and lying to you. If they say it meets the requirement of 33 CFR 183.114 then that means they have tested it for resistance to gasoline, oils, bilge cleaners, etc. and it can be used in the bilge or areas where it is exposed to these things. But that is not Coast Guard Approval. Approval means that the Coast Guard has not only looked at the item and inspected it, but also tested it to see that it meets all of the regulations that apply. The Coast Guard does not do that for foam.

    The Coast guard requirement for flotation is a performance standard. That is the boat must float in a specified attitude. How you achieve that is up to you. It can be air chambers, foam, or ping pong balls. I've even seen beer cans and plastic bottles used.

    You need to check out http://newboatbuilders.com/pages/flot.html for info on flotation.
     
  7. tunnels

    tunnels Previous Member

    3/4 foam wont even support you lunch box let alone do anything towards making the boat float !!,
    the boat Bouyancy foam and the stuctual foam are two completely diffeant things !!,
    Chop strand mat is the bottom of the strength scale !! matts and roveings are next up the ladder but everything depends on the weight of the glass per sqr /mtr.
    You really need to do a little research annd gain some understanding !!!!. :(
     
  8. Ike
    Joined: Apr 2006
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    Ike Senior Member

    I think he meant 3 to 4 inches, but still that may not be enough and it's all in the bottom. The boat will float; --------- upside down.
     

  9. tunnels

    tunnels Previous Member

    I remember in a rain storm watching a wee boat in Papeete filling up with rain water when all of a sudden it was up side down in a couple of seconds !! The floation was all in the bottom ooooh wee !!:(
     
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