Plywood bending question, replacing skiff bottom panels

Discussion in 'Wooden Boat Building and Restoration' started by Paul_A, Aug 20, 2013.

  1. Grady300
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    Grady300 Junior Member

    paul
    If you do go with the double layer be sure to use thickened epoxy along with a through pre-wet process with straight epoxy. It will use more epoxy but you will never have to worry about it coming apart.
     
  2. rasorinc
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    rasorinc Senior Member

    Bending 1/2" plywood is not an easy job. It takes time, weights and large clamps and you bend it down in stages. Two layers of 1/4" plwood epoxied together is stronger than
    plain 1/2". Stagger your joints and cover joints with 6" of bi-ax tape epoxied over.
     
  3. Grady300
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    Grady300 Junior Member

    Well said, sometimes short cuts cost you big time in the end. I am vary familiar with this design of boat and hoping 1/2" will stay put in this part of the hull could cause issues when you don't want them out in the salt.
     
  4. Paul_A
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    Paul_A Junior Member

    Like this?

    [​IMG]

    Around 45-50 pounds needed to get it flush. Think the epoxied scarf joint will hold?
     
  5. michael pierzga
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    michael pierzga Senior Member

    Sure..it will hold.
     
  6. rwatson
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    rwatson Senior Member


    Whoa - thats not a great way to hold down plywood. Weights fall off - onto feet etc

    Look up 'spanish windlass' - two layers of rope around the chines with a bit of wood twisting the two layers tight. http://www.finehomebuilding.com/how-to/tips/the-spanish-windlass.aspx



    Put them on both sides of the hull and tighten alternately - like torquing down an engine head. Put longtitudinal ( same as stringer direction ) bits of wood underneath them too.

    I once tried building a skate ramp out of construction ply, but found it starting cracking when the bend was forced.

    I put some 6 0z f'glass and epoxy on the outside of the curve, but only on the knot holes that were giving way, and was then able to force the bend in without it snapping.
     

    Attached Files:

  7. PAR
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    PAR Yacht Designer/Builder

    Plywood will take a "set" once you "talk" it into a shape. This is the easiest way to approach bending a reluctant hunk of plywood into position. Don't get greedy, just bend it around until you've gotten fairly close and wait. The following day the panel will have taken a set and you can continue bending. You can also wet the outside of the curve to help the process. Heat works good too, as does, laying bath towels over the area and pouring boiling water over them.
     
  8. Paul_A
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    Paul_A Junior Member

    [​IMG]

    Letting it set this way for a couple days prior to trimming to fit.

    Thanks rwatson for the link and everyone else for their advice.

    I'll post a pic when I have it installed and glassed.
     
  9. rwatson
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    rwatson Senior Member

    That looks a lot better. It should do the job by the looks of it.
     
  10. Grady300
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    Grady300 Junior Member

    Great idea looks good.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Convincing plywood to do what you want requires some inventiveness, as you've demonstrated. I use sand bags a lot, mostly because my yard is all sand. There are countless other methods, from ratchet straps to Spanish windlasses. You'll get 'er done, just hang tough.
     
  12. Paul_A
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    Paul_A Junior Member

    Bottom is glassed.

    [​IMG]

    [​IMG]
     
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  13. PAR
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    PAR Yacht Designer/Builder

    Way to go - see all the cussing does help . . .
     
  14. Paul_A
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    Paul_A Junior Member

    Thanks!

    This boat has spray rails that extend 10' back from the bow.

    Some guys run them all the way to the transom to give the boat a reverse chine of sorts.

    Worth the trouble or more trouble than it's worth?
     

  15. PAR
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    PAR Yacht Designer/Builder

    Well it depends on what you want, spray control or lift. If you carry the "strakes" aft, the angle can affect how the boat handles and can introduce issues, before these would normally come along. The Tolman doesn't have a lot of deadrise, so lift shouldn't be an issue, though with the strakes dragged aft, you'll gain a few MPH lower full plane speed. The difference between being on plane at 14 or 16 MPH is really meaningless IMO.

    A lot of Tolman builders use a lower rub rail which will also help control spray, so the choice is yours, but I don't think you'll gain much from the added effort of making the strakes full length.
     
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