Transom Outboard Mount Question

Discussion in 'Boating' started by Spider, Apr 23, 2009.

  1. Spider

    Spider New Member

    Messages:
    610
    State:
    Hamburg, PA
    I have a question on the spot on the transom where the outboard clamps to. On my boat there was a piece of plywood that the clamps tightened against. That is pretty much shot and needs to be replaced. It is just screwed to the transom and actually not well because all the screws looked to have been standard drywall style and all were rusted that they broke and needed to be ground flush. My question is, could I just 3/8" aluminum plate for a new piece here or do i need to stay with wood? The only advantage I see to wood is that the clamps can dig in a bit.
     
  2. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    Although it may seem silly to say it, the type of boat and its' construction would be nice to know. May not make a difference, but then again, it may make a whole lot. Also, the size of motor.
     

  3. Spider

    Spider New Member

    Messages:
    610
    State:
    Hamburg, PA
    It's a 14' Alum. V Hull and 9.9 HP
     
  4. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    Just about all of the aluminum boats I have came in contact with has a wood transom, normally about 1 1/8 or 1 1/4 inch thick. If your boat is like this, I'd take a pocket knife and try to push the tip into the wood (be careful so the knife don't close on your fingers - bad news). If the tip goes in easily, you have some dry rot in that wood and all of it needs to be replaced. If not, the wood is sound and probably the previous owner just put that plywood on there for strength or to make it a little thicker for mounting his motor. Probably nothing wrong with using some aluminum plate on the transom, as long as the motor don't wiggle around and possibly come off the boat. Be careful of what you use on an aluminum boat, as there are only several metals which are compatible with the aluminum, stainless steel being one. Don't use iron or steel fasteners.
     
  5. Spider

    Spider New Member

    Messages:
    610
    State:
    Hamburg, PA
    Well, I pulled the end caps and aluminum transom cover strip and found one side of the transom rotted. I drilled out the capacity plate and hull ID rivets, removed the transom mounting and brace bolts, then pulled the old wood out. My boat has an inner and outer aluminum wall with the wood sandwiched in-between the two.
    Now, the thickness needed measures 1.3125 (1-5/16") thick. The only thing I can find locally to replace this with is OSB Plywood. Will this type of chunked style plywood be alright to use once glued to together for thickness and sealed all the way around? From what I've been able to find, this plywood stamped "Exposure 1" is waterproof with the exception of and cut edges. I'd have to check if this stuff is stamped for that first. I have Olympic Maximum Waterproofing to cover everything.
    Appreciate any help here, this was something I hadn't planned on....
     
  6. 1sporticus

    1sporticus Active Member

    Messages:
    1,006
    State:
    Iowa
    I wouldn't use OSB. I would find exterior plywood, although you may not find the exact thickness, it is possible to glue 2 sheets together with exterior glue. I went to th elocal sawmill, and had a piece of oak sawed out. While this might be overkill, and heavy, it'll last way beyond my lifetime. Once you get whatever you use treated with some weather proofing of some sort reinstall, and use a good 3M caulking to line all of the mounting holes. Hope this helps. Later Andy
     
  7. DANZIG

    DANZIG New Member

    Messages:
    6,672
    State:
    West Virginia
  8. screamnreels

    screamnreels Member

    Messages:
    599
    State:
    Halifax county
    You could always have solid wood like oak and have it planed.I think the spelling is wrong but you know what I mean.Me I would use some composit plastic like in the sea ark transoms.
     
  9. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    OSB will swell then come apart in a wet enviroment.
    If it were mine I would get a nice piece of white oak.
    Put several coats of spar varnish on it.

    I build my canoes on an OSB topped table. Nice and slick when its new but sitting under a shelter out of the rain the surface is starting to look ragged and rough. Just from moisture in the air and the dampness when it rains.

    I don't know the exact ratio and it's probally a trade secret from manufacturer to manufacturer but OSB is a high glue content wood product.
    To thicken the glue they use sand. That is why it's so hard on saw blades.
    The glue isn't a water proof glue whereas a good bit of regular exterior plywood uses the same glue as marine grade plywood.
    The difference between the two plywoods is quality. Marine grade plywood is made to alot higher standards with few to no voids and more laminations making it stronger.
    A marine plywood would have all layers being the same wood or like type of wood whereas exterior plywood usually has junk interior layers and they aren't solid layers. You wind up with alot of voids which moisture will migrate to and introduce wet rot.