Newbie Aluminum Transom Repair

Discussion in 'Metal Boat Building' started by jhendery, Jun 6, 2012.

  1. jhendery
    Joined: Jun 2012
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    jhendery New Member

    Newbie Aluminum Transom Repair - PLEASE HELP!

    Hi Folks,

    I have a Mackenzie Runabout probably mid or late 70's.

    On the interior the transom has been refabricated and reinforced with an aluminum support brace.

    On the exterior you will notice red spots marking holes that need to be patched.

    The remaining holes are for the engine mounts and bolts that fasten the marine plywood to the aluminum transom fastened in the interior. You will notice the marine plywood template has been removed to get at the holes.

    My best guess is to have the holes welded closed. Following that reinstall the marine plywood and apply a commercial grade adhisive and water resistant caulking to the plywood that backs against the aluminum transom.

    My understanding this is not the correct way to build a transom.

    Although I am keenly interested in suggestions on what materials or process can be used to make this right.

    Thanks.

    Jeff
     

    Attached Files:

  2. jhendery
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    jhendery New Member

    Hey Folks,

    Anyone have any suggestions? I really need some help with this. Thanks in advance.

    Jeff
     
  3. Ike
    Joined: Apr 2006
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    Ike Senior Member

    Sounds like you have a handle on this. On many aluminum boats the aluminum transom is backed with marine plywood to add strength and thickness. I would use epoxy resin rather than adhesive and caulking but that's just my personal preference.
     
  4. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    JH,

    Best way is to replace the whole transom plate.

    Without knowing the extend, and cause of the holes, simply filling in with weld shall just delay the inevitable.

    If you really can't stomach the cost/time of doing that, best to make small circular discs which are some 20mm in diameter larger than the hole you wish to fill. Make sure the area is cleaned and ground out of any crap. Then use the disc as a backing plate to "fill" the hole. Weld must be good quality on both sides. That is on the transom to disc, from the outside and from the disc to the transom on the inside. Avoid stop-starts, so make it one simple action.

    This is often a good quick remedy. But looking at your transom you have so many, the better option is to replace the transom, that way you'll know what the thickness is and it shall last longer than any temp repair which you're attempting now.
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I see a number of issues with this transom, first is she looks to have had her cutout raised, likely to accommodate a 20" shaft engine, yet the transom skin wasn't raised, just a length of angle stock, possably over the plywood core, added. A pretty Mickey Mouse arrangement, to say the least.

    I agree with John in that the transom skin has enough damage to warrant replacement. If this is too much, you could consider more plywood (2 layers of 3/4" minimum), well bonded (epoxy) to the inside of the transom skin, with bonded holes to either plug of isolate the penetrations. Considering all the holes and the cutout, a lot of work, but something that can be done in your driveway.

    The "Cliff's Notes" version would be to to sand the inside skin clean with 80 to 100 grit, then immediately clean and coat with straight laminating resin. Before the resin cures, mix up a thickened batch of milled fibers and silica, to a peanut butter constancy and using a 1/4" notched, trowel skim coat the whole inside skin. Position the plywood core in place and clamp lightly, insuring good adhesive contact. Run some drywall screws through blocks of wood (protect with packaging tape) in all the holes from the outside, to help "suck down" the skin to the plywood. On the inside use your gloved finger, around the edges of the plywood and make a small fillet of the epoxy ooze out. Let this whole thing cure a day or two.

    Remove the temporary fasteners and blocks, then drill out each hole with a slightly bigger bit, all the way through the skin and new core. Apply tape over the back of the holes, then wet out inside them with neat epoxy. Let this dry, until just barely tacky, then fill each hole with more of the thickened mixture. Sand smooth and coat the raw plywood with at least 2 coats, preferably 3 of neat epoxy. You now have sealed and bonded the holes and a new core in place. This will accept up to about a 60 HP engine without issue. When you drill new holes for the engine mounts, bond them just like you did the other ones, making them at least 30% larger in diameter then the actual bolt shank clearance hole needs to be. This will guarantee water can't get back into the core and rot things out. In fact, any and all penetrations into the transom core should be bonded in this fashion.

    Log onto westsystem.com and systemthree.com and download their users guides, which will explain these techniques. You'll still have a transom full of holes, but they'll be sealed reasonably well, you can do it in your driveway and if you don't drop a 150 HP engine on it, you'll likely be fine for a decade with minimum care and a few decades with reasonable care. Under putty and paint, know one will know a thing.
     
  6. jhendery
    Joined: Jun 2012
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    jhendery New Member

    I appreicate everyone's feedback - thank you.

    I am really a novice DIY person without many of the skills required to repair the transom including welding.

    I should also mention the interior portion of the transom has been fabricated with an aluminum support brace welded to the aluminum runners along the floor length of the boat and vertically up the interior transom skin. There is no possibility to install plywood to the interior transom skin since the fabricated support brace is in the way. I will post an interior pic to visually aid my description.

    Agreed the best option would be to replace the exterior transom skin with a new piece of aluminum. I think this is major work that I'd like to avoid.

    That being said I 'think' my best option is to repair the holes from the outside transom skin. As far as I can tell that leaves me with two choices.

    1. Weld plates to the existing holes. This will leave a non smooth finish making it difficult to seal the marine plywood to the transom.

    2. Epoxy or fibreglass the exterior transom skin. Then reinstall the marine plywood using a comercial grade caulking.

    Are epoxy or fibreglass even options to seal holes on an aluminum transom?

    Thanks in advance for the suggestions. Keep them coming.

    I will post a picture of the interior transom tonight.

    Jeff
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A single thin skin of aluminum isn't going to support your engine, even with braces. Remove the braces, install the core, then reinstall the braces.
     
  8. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    Can't really see much to form opinion. Do you have more pictures, what size engine your going to put on it?
     
  9. jhendery
    Joined: Jun 2012
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    jhendery New Member

    Here are more pics.

    The first three show the interior with aluminum support brace. And two more of the left and right side showing exterior transom.

    I run a 70 horsepower outboard. The engine was mounted on the boat and ran well. The issue is the leaking.

    How should the exterior holes be patched? Would epoxy work to seal the holes? What about fibreglass?

    I will post another pic showing the marine plywood in the morning.
     

    Attached Files:


  10. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Wow, some really serious Mickey Mouse work going on there. If you think this transom is just in need of some holes being patched, I've got nothing more I can tell you.
     
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