princecraft aluminum boat transom repair

I have a 16 foot aluminum princecraft, After I bought it I found some electrolysis on the transom, holes through the aluminum to the plywood core. Friends told me this was from it being kept in the water with no zinc. So I covered the holes with caulking and got a zinc this was last year. I keep the boat in my yard out of the water when not in use and was surprised to recently notice new signs of electrolysis on the transom, there are no signs of corrosion anywhere besides the the transom but, it is both inside and out. I'm thinking the plywood core must be wet to be causing this. I've been told I could cut a piece of aluminum checkerplate and attach it to the outside with sikaflex and screws or get it welded on, does this sound like a good idea? I'm thinking I should do something to fix it before next boating season and it's supposedly a 1996 hull so it's not worth spending too much money on. Anyone have any experience with this? Thanks.

Re: princecraft aluminum boat transom repair

Hi floatmiboat. I believe what is actually happening is that someone replaced/repaired the transom with pressure treated lumber over the years. This is a major no-no on an aluminum boat. Treated lumber uses Arsenic and/or Copper as a preservative. These dissimilar metals then react with the aluminum in the hull to produce electrolysis. You'll need to remove and replace the transom with one made from non-treated plywood, sealed with epoxy or polyester resin and fiberglass. You can do it yourself for a couple hundred bucks. I would also remove any silicone you may have used and fill the holes with JB weld, if they're smaller than the size of a dime. There are tons of threads here in the forums that can walk you through the job.

Re: princecraft aluminum boat transom repair

I'd replace the wet transom and re-skin the aluminum from the inside with the new aluminum (old street sign or something). I've also seen it done from the outside http://forums.iboats.com/showthread.php?t=472217&page=5

Re: princecraft aluminum boat transom repair

ezmobee said:

I'd replace the wet transom and re-skin the aluminum from the inside with the new aluminum (old street sign or something). I've also seen it done from the outside http://forums.iboats.com/showthread.php?t=472217&page=5

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That's what I did on my 14' Grumman which had a pressure treated plywood transom core and caused the skin to look like Swiss cheese. I replaced the core with two sheets of exterior ply glued together with PL and sealed with epoxy. I purchased a sheet of .062 thick 5052 aluminum and then cut a piece to match the exterior profile of the transom. After killing all the corrosion, I had the exterior skin MIG welded on over the existing skin. I then sealed all the holes with Marine Tex from the inside. Using the inner skin as a guide, I piloted the fastener holes into the new transom core through the new skin. I then removed the core, drilled the holes oversized, potted them with a mixture of epoxy and carbosil and reinstalled it. Then, I back drilled from the new exterior skin through the potted holes in the core and installed rivets and bolts. Since the holes in the wooden transom were potted with epoxy, I don't have to worry about the new core getting wet. I sealed the inside of the rivets, bolts and old weld seam with Gluvit and will apply Steelflex to the outside. Now it's as good as new if not better since the skin on the transom is .125 thick (double what it was) and the core is at least twice as strong as the original. That 635 epoxy is some great stuff to work with and is very strong. The trick is to make doggone sure that you kill all the corrosion before applying new skin over the old which is easier said than done. It requires a lot more sweat equity than actual money.

Re: princecraft aluminum boat transom repair

Thanks for the tips guys, it's possible that a previous owner has replaced the core with pressure treated ply, but, it seems doubtfull based on the other maintenance done on the boat. There are definitly signs that someone was repairing the transom exterior, there is a long piece of stainless sheet metal on the inside of the transom which was hiding some of the corrosion. The worst holes are about 1/4'' in diameter and there are none in the lower area of the transom which is just aluminum sheet. The upper part of the transom is a sandwich of aluminum and ply with a cap. I also noted some corrosion around some of the added stainless steel screws. Mojo^ I have been told that the metal on these boats is too thin to weld is that incorrect? I'm unsure of the gauge but it looks to be 3/32 or so. I like the idea of getting a new skin welded on as the interior of this one could be compromised.

Re: princecraft aluminum boat transom repair

Not true. The guy that welded mine gave me an example of his skill by MIG welding two beer cans together with no burn through. I was completely overwhelmed as I never thought anyone could do such a thing. Most places will probably want to TIG weld using a wire spool gun. This is much faster and therefore will cost less but it is inferior to MIG welding which actually fuses the metal rather than just shooting a bead of molten metal on top of a seam. You just need to call around and find the right welder. The guy I used is retired and runs a small shop in his backyard. I found his card posted in a local hardware store.