Replacement gunnels out of 3" square housing pvc pipe?

Discussion in 'Boat Design' started by valvebounce, Apr 20, 2020.

  1. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    I have a fibreglass rowing boat,10ft long.with a 6ft beam.The boat is very stable in the water.
    The Gunnels are soaked with water,which makes the boat a lot heavier,and hard to handle out of the water.The bow,middle and stern seats have been constructed with 3"X 3" timber and are fibreglassed down to the deck.These are also water soaked.The weight of the boat must be nearly double what it should be.I plan to cut the fibreglass off the gunnels and remove the timber,then replace the gunnels with square pvc pipe,then fibreglass them in.I will need to heat the pvc pipe to follow the curvature of the boat.I have customized some aluminium oars and the boats rows really well.
    I will need to make some substantial rowlock supports in the pvc gunnels.
    The boat goes very well with a 6hp Evinrude on it.
    I intend to make new seats that are simply flat board to cut down on the weight.
    Anybody attempted a similar project,and got any suggestions?
     
  2. kapnD
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    kapnD Senior Member

    I can’t imagine 3”x3” lumber anywhere on a 10’ boat. Severe overbuild?
    Got pictures?
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    I haven't even got 3x3 holding the roof up ! If you use something as a former to glass around, it will go a lot easier if the corners have a good radius, otherwise it will be like when you were a kid, and had annoying bits of hair sticking out of your hairdo, and you needed some Brylcreem ( V will know what that is) :D
     
  4. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    How about using PVC tube instead - maybe about 2" diameter at the most?
    Tube will easily bend around your gunwhale.
    And you can fill the 'gaps' on the inside with low density filler, prior to glassing over the whole lot.
    The fibreglass should 'wrap around' a hollow tube much more easily than a square tube?
     
  5. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I heated some PVC pipe in oven at 300deg for about 5 minutes to make sheath for 1.5" chisel. Stuff gets soft enough, but is also springy and wants to return to original shape. So for second attempt I filled the sink with water and using some oven mitts and towels, pressed the hot pipe around the tool and dunked everything in the water to instantly cool, and it worked great and held its shape, and doesn't seem brittle or anything.

    Heating a long pipe evenly might be tricky. I guess you could attach a metal conduit pipe to a heat gun or propane torch, with a few big wires around the metal pipe to keep it from direct contact inside the PVC, and play it in and out of the PVC for a bit until it begins to soften. Maybe put the PVC in a bigger pipe with cap on one end in addition so the heat can penetrate from both sides, and use additional external heat on outer pipe.

    I consider PVC to be the Poor Man's kydex.
     
  6. valvebounce
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    valvebounce Senior Member

    The present timber on the gunnels is about 2"x 2" glassed over.The 3"x 3" would be square section downpipe.
    I'd prefer oblong section say 3"x 2" if I could source it.
     
  7. valvebounce
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    valvebounce Senior Member

    Gooday Mr E,hope you are well.
    I used silvercrin,not Brycreem. You could only wear a shirt once because the collar greased up.My curly hair and my Tony Curtis Teddy haircut took some taming.(Teddy boys--Bodgie boys) Haha
     
  8. valvebounce
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    valvebounce Senior Member

    I won't mind the bulk of 3"x 3" square section,it will act as a buffer.Some of the places I intend using the boat and docking it are a bit rough.
    The problem with round pipe would be filling round it before it is fibreglassed.I would have to fill it from the top,and flip it over to fill the underside.
    I intend clamping the pvc square section pipe and heating and clamping as I go.I've replaced wooden gunnels using a similar method,but using steam.
     
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  9. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    Thanks for your input,I intend clamping the square section pvc pipe as I go,and heating it with a heat gun.
    If I leave it to cool and set with it clamped in position,I can fibreglass it in sections and then fibreglass the sections where the clamps were when I remove them.(Hopefully)
     
  10. Blueknarr
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    Blueknarr Senior Member

    I Don't like raining on parades, but...

    Fiberglass over square corners is a real PIA. And no amount of brilcream will help.

    I'm not sure why round stock would be harder to fill than square.

    Clamping heat softened PVC will leave serious marks.

    I have put PVC tube gunalls on a dingy by
    Slicing one wall wall with a table saw. Remove slightly less material that the dink's FG thickness.

    Pry it apart to insert the dingy. It's own clamping pressure will hold it in place while it is glassed over


    Good luck
     
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  11. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    PVC pipe is frequently used as a shape to glass over.

    As mentioned, square corners would be slow and difficult to laminate around. Round pipe is cheap and easy to buy.

    There are several ways to warm it to shape it. You can get heating blankets to wrap around the pipe, this let's you make nice bends. Hot water, heating ovens and other things can work too.

    You may be able to rent a heating blanket.
     
  12. kapnD
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    kapnD Senior Member

  13. kapnD
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    kapnD Senior Member

    PVC heaters are common in the electrical trades work, can probably be rented.
    A propane torch works, but take care not to singe material!
    When correct bend is achieved, it can be rapidly set by wiping with a wet rag.

    I like to wrap high wear areas like dingy gunnels with some old fire hose, it’s very tough stuff.
     
  14. bajansailor
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    bajansailor Marine Surveyor

    Apologies for a bit of Fred Drift, but a question for Kapn D - what type of dinghy are you building in the photo above?
    I presume that she will have a longitudinal seat giving buoyancy and flexibility for the rowing position, depending on if you have a passenger or not?
    VB, you could also consider inner and outer gunwhales as per Kapn D's photo - I am guessing that they cannot be more than approx 1.5" x 3/4"?
     

  15. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    I wouldn't have any trouble finding round pipe,what I meant was,I would prefer rectangular section,rather than square,but It's harder to source.
    What do you think of putting cuts on the inner bends to allow for the curvature?The whole thing would end up waterproof after it was f/glassed.
     
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