Old Boat Repair- Stress Cracks

[mchristoffersen]

I recently acquired a jon boat and outboard, both from the late 70's. The jon boat is a 14 foot lowe line and the outboard is a 20 hp mercury. Both had apparently been sitting out in the elements for more than a year, and in a barn for a few years before that. The plywood transom was extremely rotten, it had the texture and strength of soaked corrugated cardboard. The boat has two large stress cracks just forward of the transom, and another one in the center (see included pictures). The one in the center appears as though is was JB Welded over a long time ago. My question is, are these cracks just because the outboard has been hanging there for years with a totally rotten transom, or is the 20hp outboard simply too big for the boat? I plan to have the cracks welded and than patched over with more aluminum, and possibly to reinforce the transom with more aluminum, either riveted or welded (Advice?). The transom also is also buckled out a little, which I believe was the cause for the epoxy being broken off crack #3

Addendum: I cannot get the photo of Crack #1 to upload, but it extremely similar to Crack #2.



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[MrTotty]

I would have a plate made for the transom that went all the way across, you can rivet or weld it in several locations. That will also straighten it up. The sides I would just have rewelded. It looks to me that the rotten transom was the cause of all of it. A bouncing motor can wreak havoc on a busted transom.

 

[Ranchero50]

Yep, pretty normal 'damage' from a rotten transom. Cut the corner caps off with a circular saw set to 1/8", bend the top cap up, replace the transom wood and bend the cap back down. Have a welder put the corner caps back on and fix the front cracks.

 

[riverbud55]

Ranchero50 » Tue Aug 27, 2013 7:05 am[/url]"]Yep, pretty normal 'damage' from a rotten transom. Cut the corner caps off with a circular saw set to 1/8", bend the top cap up, replace the transom wood and bend the cap back down. Have a welder put the corner caps back on and fix the front cracks.

Seeing your going to be at the weld shop anyways much easier and cleaner looking is to cut the transom brace out low enough to tilt the old wood transom out from the bottom and put the new one in later,, then reweld the brace,, done 2 boats that way and getting ready for a 3rd,, own a sheet metal weld shop, in most cases wouldn't even consider to do it any other way,, took me less then hour to r&r my transom in my Valco,,, all the lowe(as most budget cookie cutter boats do) boats I have seen have really wimpy transoms

 

[shawnfish]

riverbud55 » Yesterday, 22:49[/url]"]

Ranchero50 » Tue Aug 27, 2013 7:05 am[/url]"]Yep, pretty normal 'damage' from a rotten transom. Cut the corner caps off with a circular saw set to 1/8", bend the top cap up, replace the transom wood and bend the cap back down. Have a welder put the corner caps back on and fix the front cracks.

Seeing your going to be at the weld shop anyways much easier and cleaner looking is to cut the transom brace out low enough to tilt the old wood transom out from the bottom and put the new one in later,, then reweld the brace,, done 2 boats that way and getting ready for a 3rd,, own a sheet metal weld shop, in most cases wouldn't even consider to do it any other way,, took me less then hour to r&r my transom in my Valco,,, all the lowe(as most budget cookie cutter boats do) boats I have seen have really wimpy transoms

you don't even have to cut the transom brace just take a chisel and hammer and the rivet heads knock right off then take a Phillips or something similar and tap it out. all them old lowelines(lowes) transom wood can be removed without cutting corner caps etc,,,, the wood should come down with the brace removed and there may be a strip of 90 aluminum to be removed that holds it up into the transom cap, my jumbo V had it and it comes off easy its just riveted... if you get the cracks welded up id do like the guy above said and make a transom plate. that along with new wood sealed up and it will last forever. I was surprised that my transom was 2 separate sheets that equaled 1 and 3/8 I believe. wasted my time though after I removed it I put each end on a block and jumped up and down on it and had no flex whatsoever....so I put it back in.......

 

[mchristoffersen]

You guys are right about the transom, I just drilled out the rivets holding in the bottom strip of aluminum and could pull the wood out easily. I am going to get the cracks welded the week after next. Is there any easy way to cut aluminum other than with a plasma torch (I do not own)? I have been raised to believe you cannot easily cut it with oxy-acetylene (I do own), but I have never tried.

 

[Ranchero50]

Oxy will melt it but won't cut it clean, Aluminum acts like solder, just without the color shift before it melts to liquid. Use your saw of choice or even a cold chisel will work wonders on aluminum.