Stringer / bulkhead help

Discussion in 'Fiberglass and Composite Boat Building' started by alyons05, Oct 6, 2020.

  1. tpenfield
    Joined: Dec 2016
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    Location: Cape Cod, MA

    tpenfield Senior Member

    Good point about epoxy . . . I think it is best for a first-timer to use a poly resin so they don't have the complexity and issues of trying to put poly over epoxy, since in their situation, it probably won't adhere and they will have a hell of a mess on their hands. If they want better adhesion, there is VE resin. If they need a slower cure time (open time) there are 'slow' catalysts.
     
  2. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    Don't rush. Take it from someone who's done an entire restoration. If you have to wait until spring in order to do a good job that will be a better option for you. You'll also have a chance to think the job through thoroughly, plan your work and save up some money for the job. A good book to look at is Dave Gerr's classic text "The Elements of Boat Strength". It will give you some ideas that will help you understand how your boat is (or should be) constructed.

    Alyons05, you raised a couple of questions. Regarding rebuilding your stringers. You can use marine plywood as a former. You certainly could seal the stringer with epoxy to keep water out. You'll need three coats to build enough film thickness to prevent water intrusion. You don't need to use plywood as a core however. A number of different materials can be used. I rebuilt the stringers on my inboard cruiser over a decade ago. I used Owens Corning Formular 250 Extruded Polystyrene Foam. Yep, I used foam insulation material right out of my local Home Depot.

    You're probably thinking "It's just foam. How could it possibly be strong enough?". Well, unless your boat uses something like solid timber stringers (no fiberglass boats do), the core of a stringer adds no strength at all to the structure. It's the fiberglass laminate that is draped over the core that provides the strength and carries the loads. I'll post some photos from a decade ago that show how I built my stringers. They are as solid today as they were back then. Note: The wood inserts provide compressive strength that the foam would not provide. The 4 inserts are located where the inboard engine beds are placed.

    IMG_0778.JPG IMG_0242.JPG IMG_0243.JPG

    17/08 biaxle stitch mat is 0.044 inches thick. Your boat is about 20 feet LOA? Beam about 8 feet? If so the fiberglass laminate should probably be about 0.20 inches thick or about 4 to 5 layers of that mat. You'll need to learn how to do the layup, tab the layers into the hull and fair the transitions so that you get a nice strong structure. System Three and West Systems have both produced nice downloadable books that will help you through this process.

    Take a breath and try to be patient with yourself and your boat.

    Oh, and good luck and welcome to the forum!

    MIA
     
    Last edited: Oct 8, 2020
  3. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Depends where you are on the weather.

    For example, no way would I start that anywhere north of Chicago unless you are by the sea.
     
  4. alyons05
    Joined: Jul 2010
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    Location: USA

    alyons05 Junior Member

    The original stringer has inconsistent thickness of the glass on it so I can’t figure out how many layers of 1708 cloth to use to re glass the stringers. Without going over board what would a safe layup be? The stringers are only 5 1/4” high at their max point. I was planning to use 6” cloth. Placing the first layer about 4” on the hull and 2” on the stringer, second layer half and half, third layer 4” on the stringer 2” on the hull then a cap to cover the top.
     
  5. alyons05
    Joined: Jul 2010
    Posts: 12
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    Location: USA

    alyons05 Junior Member

    I am actually in a suburb of Chicago. If I waited till spring would it be bad to transport the boat 425 miles one way till spring with a stringer removed and then transport it 425 miles back home? I am worried that a 850 trip with a missing stringer would or could cause damage.
     

  6. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Damage from transport depends on how much of the stringer was removed and the support from the trailer.

    As for spacing the stringers off the hull.

    Most smaller boats don't have stringers spaced off the hull, the stringer grid is assembled and dropped in placed, then glassed over. There's no bedding compound or putty used to form a radius.

    While spacing is better, few smaller boats are built that way.
     
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