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Need ideas on replacing club's jon boat transom

May 4, 2005
4,062
Macgregor 26d Ft Lauderdale, Fl
HELP!
our sailing clubs large jon boat transom was rotted, and I removed the wood last weekend.
Now I need ideas on how to replace the transom!

*We don't think this boat can be welded, due to age, and aluminum corrosion. -so we have not removed any of the rivets, as we don't think they can be reattached (support brackets).
20160618_115145.jpg


we are thinking of doing some kind of 3 piece transom and a long brace to hold it together, and some through bolts, (above waterline). -(This is the race committee boat for dingy racing, & max hp will be 8. )

suggestions appreciated!

20160618_115314.jpg
 
Mar 23, 2009
139
Rafiki 35 North East, MD
I'm not sure I understand your question but I would do two plywood panels, one on either side of the transom, and then a piece of solid wood across both panels to join them together above the bracket attaching the transom to the floor, making sure the solid wood piece won't interfere with the mounting clamps for your outboard. I would probably use pressure-treated wood rather than marine grade ply given the utilitarian nature of the boat, though I would give the wood pieces a good coat on all sides with an alkyd enamel or similar paint after cutting them to size but before installing them. Then I'd hold it together with some through-bolts to acorn nuts above the water line.

We did something similar when replacing the rotten transom and seats in a 10' aluminum row boat we bought off of Craigslist on the cheap. It has been in my back yard for 7 years since then and seen occasional use with a 5hp outboard along the waterway behind my property and it has held up just fine. If you find the boat leaks along the seams due to expansion or corrosion around the rivets, you may want to try the gutter sealing products they now sell at home centers. Not the most elegant of fixes but very effective.
 

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
Replace the wooden transom with marine ply, glassed and epoxied. Drill out the rivets on the side angles and bottom brace, insert the transom panel, and rivet the angles and brace back in position. Through-bolt were required. Get yourself a tube of 3M 5200, wire brush, and solvent wipe anything that looks like a leak and lay on the the 5200. Make sure you source marine-grade all-aluminum rivets of the proper diameter and length.
 
Sep 8, 2014
2,551
Catalina 22 Swing Keel San Diego
Go with what Gunni said, but before you do any of that... Go to a welding supply store (Google AirGas or Praxair). Get a spray bottle of Aluminum cleaner, its a mild acid specifically made for cleaning aluminum prior to welding. Spray and let sit for 3 minutes, spray again and scrub with a scotch brite pad, spray again and let sit... repeat till clean. The acid is not strong enough to burn your skin, but gloves aren't a bad idea and eye protection is a must; like most cleaners it would burn in your eyes. Flush with fresh water when done. With any aluminum repair, even if you don't weld anything, you want it as clean as possible.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
ive replaced thr wood in the transoms on several aluminum fishing boats... its an easy task, and using marine plywood, you dont need the thick stuff becaus you can laminate 3 or 4 pieces of 1/2" together to get the thickness desired...
and in that type of boat it doesnt need to be enclosed with epoxy, as its open to the weather and it should last many years before it rots again, depending how its taken care of...

the rivets can be removed as desired, and new ones installed very easily and quickly with a rivet set in an air chisle tool, with a buck bar to back it up.

after removing the corrosion, if the aluminum is still strong enough to use, its thick enough to weld... if the welder has a clue what hes doing.

im on my phone so i cant see the photos too good, but it looks like the basic old fishing boat transom, where the aluminum shell of the boat holds the water out, and the wood transom is attached inside the aluminum skin to give support for the motor to hang on...
repair the skin as needed, and bolt the wood in like the old one was attached... the boat is probably 40+ years old and none of us will know or care if it ever rots out again...
 
Mar 23, 2009
139
Rafiki 35 North East, MD
I did not understand from the picture that the bracket is no longer attached to the transom and was thinking the wood was just providing a place to mount the motor. Since it is structural, I agree with the suggestion to use marine grade plywood but also agree with Centerline that encasing the plywood in epoxy is more than is necessary for this application.
 

Gunni

.
Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
The purpose of epoxy glassing marine plywood extends far beyond waterproofing, it greatly strengthens against bending and torsional force. It is the difference between flat plate and an I-beam. You create a web.
 
May 4, 2005
4,062
Macgregor 26d Ft Lauderdale, Fl
Thanks for the tips, I'll look for the aluminum cleaner.

this boat has a middle support bracket that was bolted to the wood. from inside the boat. I didn't want to remove it, since it seems to be working, although two rivits have pulled thru on the bottom of the boat. I figured we'd fill it with lifecalk.

-I was thinking of cutting the top of the aluminum transom, so I could slip some marine ply in the middle.


I'm nervous to try installing rivets on a boat, since I've never done it before



-we have inflatables, but this one holds 4 people and has a bimini, so it would be good to get it back in service.
 

Gunni

.
Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
That aluminum square-section on the top of the transom is structural, leave it in place. Rivets are easy to master. 316 stainless steel, with washer's as needed and lanocote, or nylon for galvanic isolation. You are carrying passengers, do it right or abandon the boat for new..
 
May 4, 2005
4,062
Macgregor 26d Ft Lauderdale, Fl
Gunni, where would I find the tools and parts to do a proper rivet?

I have done hundreds of pop rivets, but no real rivets like I see on this boat. -looks like I'd need air tools or hydraulic for this size/strength.

-note: this boat is used on a 5 acre 'lake' that has max dept of 12' and is off the icw. (no wake zone)
its not going to see much use beyond dropping marks and ferrying passengers and no wake speed.


https://www.google.com/maps/place/G...83330d29acfaf3!8m2!3d26.0166235!4d-80.1234294

it just needs to support a HP 8hp 4stroke and be dry.

I found this video..
is this the way to go?
also found some repair kits.
 
Last edited:

Gunni

.
Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
A 316 stainless pop rivet of the same diameter as the solid aluminum aircraft rivets will do the job. You will need to seal them to make them waterproof. Just use a quality rivet tool.
 
Apr 27, 2010
1,157
Hunter 23 Lake Wallenpaupack
I did some small repairs on an old $80 jon boat similar to yours. I tried the aluminum welding rods you can buy at a big box, to repair a small seam crack. Sort of worked - I could not really get the surrounding metal hot enough with my propane torch, but the rod did melt and provided some degree of structure over the cracked area. I then sprayed on the black gooey "rubber" paint (Rustoleum branded) I got at HD on the inside. That may work (though you should not need the rod) for any loose rivets. I have tried Bondo and filled epoxy in the past - works, but the temp changes tend to eventually cause it to crack. But so what - just redo it.
Those hefty stainless rivet tools can be pretty pricey, I think, so consider that tradeoff before removing the existing good rivets. I think I might put it a center wood piece behind the upright, but about 1/3 the width of the transom (that is, not a narrow vertical), then a pair of pieces on the sides. It looks like you should be able to slide them in after the center is in (or if the transom flexes enough, maybe do the center last - especially if built up from thinner panels). You will probably need a horizontal up top in any case, to create enough thickness for the motor clamps (like mine), say about 3/4 thick. If you epoxy and bolt that, I'd think it's be strong enough for an 80 lb or so outboard. I don't even have a vertical support like yours, though maybe mine is 5hp rated.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
I Agree with Gunni about leaving the structual in place, as you can do anything except disrupt what has been working fine for a few years... get the brace out of the way and cut the wood to fit.
and I also agree with the assessment of epoxy over wood, BUT... for the jonboat transom its overkill and only adds extra work to an otherwise 3-4 hour project... and it will probably cause premature problems because if the holes arent sealed so water cant leak in, the wood WILL rot very quickly in its encasement because of the sun shining directly on the part and so it will be moist and warm inside... and as fine as this may seem for some "wood";), its not good for transoms.

I would also do everything possible to stick with aluminum rivets in the aluminum hull.... the rivets can be found at any truck/trailer repair center, because its the same type of rivets that they use to hold the roof and side skins on truck trailers with.....
and if you were to take the boat there with you, you could probably have a few rivets set for free while you watched... it would take about 5 minutes to set the 4 rivets in the transom brace to the bottom of the boat.
and there is no sealer necessary because the rivets mushroom out in the hole so tightly water cannot find a way thru.... even in oversized holes...

but I would not consider going thru the work you are and just filling the holes with sealer and calling it good.
 
May 4, 2005
4,062
Macgregor 26d Ft Lauderdale, Fl
Thank you ALL!
I'll take these ideas back to the club... see what the consensus says.

I'd hate to make it too nice, someone would steal it!
 

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