stringer and transom info - replace transoms with something other than plywood?

Discussion in 'Boat Design' started by jimmy wise, Nov 4, 2013.

  1. jimmy wise
    Joined: Nov 2013
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    Location: reno nv

    jimmy wise Junior Member

    thanks i will just thicken some resin and seal the holes. they are 1 inch and go into an 11/4 hole because of the angles to drill. they are about 6 inches long due to the design of the bildge area. what about through bolts for the out drive? should i drill oversize and fill with glass and re drill holes so the wood dosent crush and move with time?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Yes, this is one way and effective too. Just drill an over size hole, saturate the surrounding wood, pack it full of thickened goo and when dry, redrill the now plastic filled hole to the appropriate size. I usually round over the edges of this hole and at the bottom, where it land on the planking (or whatever) I feather out the fillet to make a clean entrance and exit through the weep hole. All holes in wooden boat parts should be done like this, as it solves so many issues.
     
  3. jimmy wise
    Joined: Nov 2013
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    Location: reno nv

    jimmy wise Junior Member

    i found fibreglass tubing for transom through bolts. im checking on ordering. if its cheap ill drill wood oversized and glass tube in and finish to perfect size
     
  4. Ilan Voyager
    Joined: May 2004
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    Location: Cancun Mexico

    Ilan Voyager Senior Member

    I agree totally. It's simple, cheap and very effective. The same has to be done with foam and honeycomb. For transoms destined to be pierced (for installing outboard engines for example) before glassing I cut the oversized holes, fill them with a goey of silica and cut fiber, do the lamination and make the definite holes when installing the engines. I seal the holes with high temp silicone for engines. That seals really. If the engines are powerful I add aluminum compression tubes sealed with polyurethane or technical silicone so nothing will be crushed when tightening the bolts which are greased with silicone grease for diving gear to minimize electrolytic problems. That last a very long time, easily more than 20 years. the evil is in the details...

    For simple transoms which do not support outboards a simple way to get thickness in a laminate is to use coremat or similar. A well made coremat is only slightly heavier than plywood (about 600 kg/m3), and being sold in rolls 2 feet wide the shipping remains cheap.

    Achtung cobalt is delicate to handle, and never, but never let it be in contact with peroxide, except mixed in resin. Another way to get strong and thick transoms when plywood is not available or not desirable is to use light cedar planks in two layers at 45 degrees. The wood must be prepared; a first coat of polyester resin with 0.5 to 1% cobalt added and diluted with styrene. The total mix is catalyzed with 2 % (in weight) of peroxide.
    The cobalt helps the resin to cure completely even being in contact with wood which has phenols (inhibitors of polyester resin). I wrap the planks with 2 or 3 mm Coremat That gives a rather good base for the further lamination. I prefer this solution over plywood, because good cedars hardly rot, and an eventual rot will only affect one plank.

    It has not the durability and strength of epoxy, but it's acceptable.
     
  5. MassimilianoPorta
    Joined: Apr 2019
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    Location: Italy

    MassimilianoPorta Junior Member

    Hi, very interesting... what is an aluminum compression tube?
    Do you have a picture or a video of your work?
    Thanks
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Old posting, but I think he means a thick-walled tube that is contained by the washers both ends, to prevent over-tightening crushing the panel.
     

  7. MassimilianoPorta
    Joined: Apr 2019
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    Location: Italy

    MassimilianoPorta Junior Member

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