Project 2 from DaveO: aluminum canoe refit

[DaveO]

Sorry I don’t have “before” pictures for this one: I picked up this Grumman canoe from a neighbor for $20, its approximate scrap value. While he was having some yard work done a backhoe grazed the canoe. (Note for future reference: in a fistfight with a canoe, the backhoe ALWAYS wins.) It was dented pretty badly and the “spine” that joins the two halves of the canoe at the end was crushed and bent, but seemed fixable.

These canoes sell used for $400 - $500 so my goal is to repair the canoe into useable shape without spending $500 in time or materials. I removed the seat and the “bulkhead” inside the canoe to access the dented areas, then evicted a nest of mice that had colonized the floatation foam in the dented end.

Before I disassembled it I had hammered out the dents as best I could, but the spine was still badly bent and no amount of hammering would fix it. Grumman stopped making replacement parts for this canoe (according to the very friendly and informative tech support guy I spoke with) so I decided to repair it. I used a small dremel grinding disk then a hammer and punch to remove the original Grumman rivets. I welded up a steel form and hammered the spine against it to remove the bends.

McMaster Carr had aluminum pop rivets of sufficient strength for the replacement rivets. The original rubber strip in between the riveted surfaces was too FUBARred to reuse, so I replaced it with 3M Marine Caulk. I riveted a few inches at a time, applying caulk and clamping as I proceeded. The photo shows a bolt and nut I used to “index” the holes and to draw the surfaces together for riveting.

The photo below shows 6 or 8 inches of rivets, maybe 25% done- this project is turning out to be more of a scrape than I’d anticipated, and may start to bump up against the “too much grief for not enough payoff” threshold.

Next steps after riveting will be to replace the internal flotation foam, then re-install the seat and the inside bulkhead.

Photos
~ the form
~ "before" riveting
~ intermediate riveting phase

[Wrenchtamer]

Glad to see you are finally tackling this project!! Keep us updated.

[DaveO]

I will- for this start at riveting I was disappointed with the way the smaller rivets turned out: they'll need a lot of cleanup, and they leave a hole where the mandrel popped off. Probably going to be a collection point for mud and mildew. The first 6 big rivets snapped off flush with the outside surface. Also, I need to "tune" my riveter, or something, because I wound up having to disassemble it after every pop to remove the mandrel.

[jakeru]

I hope you can get it out and paddling successfully. That dolly looks serious!

If you are having problems with the rivet not "popping" during installation, you might try adding some backing washers (available in aluminum, really cheap) to your pop rivets. They help the pop rivet fasten thin, weaker material, or where holes are drilled out slightly oversize much better. They are installed on the opposite side from where you insert the pop rivet from. Another tip that may be helpful is, try to compress the "material sandwich" together during installation, if possible. You can press down with the riveting tool but might need something behind to press against the material. (Perhaps a "rivet relief" hole drilled into your dolly might be "just the ticket".)

Edit: I took another look at your picture, and have another idea about what could be going on with your smaller rivets. You might need a different piece that screws into the nose of your pop riveting tool, with a smaller ID, for the smaller rivets. See if you can find a piece that screws into your pop riveting tool that has an ID that matches the OD of the "stem" coming out of your pop rivets.

[DaveO]

Thanks, Jakeru- I'll take a close look at the rivets from underneath to see if they're within spec. Fortunately I do have access to the blind side- the rivets are the right size for this application according to the McMaster Carr catalog, but they might be a touch undersize for the hole. The backing washer tip may be just the thing.

[jakeru]

Dave - this picture might help explain the different pop rivet tool inserts:


You can see on this particular tool, there are four of the inserts (one in the head of the tool, and three stored in the handle/frame of the tool.) If your tool is like the one pictured, just make sure to put the right insert in the head, to fit snugly around the pop-rivets you are using. (The inserts just screw in.)

[DaveO]

Yup, I'm with ya: I was using the smallest diameter nosepiece I have. The problem I had was that the mandrel was itself deforming: after the rivet popped the mandrel remained with a ball shape on the end, and wouldn't fall through the jaws after popping. I wound up removing the outer shroud, clipping the mandrel end, re-assembling, and then letting the mandrel drop out.

Do you know if that balled end on the mandrel means something? I'm starting to get a bad feeling...

[jakeru]

Proper pop rivet installation should leave the bulbous part of the mandrel stuck inside the rivet body, immediately behind (and drawn up tight against) the back side of the material sandwich.

If the bulbous part of the mandrel is getting pulled through your material sandwich, you've only got a limited amount of friction (applied to the ID of the hole) holding the pieces together.

I've had the bulbous part get drawn through relatively weak plastic sheet, which I was pop riveting to an aluminum sheet. The holes in the plastic sheet were just expanding and the rivet had very little holding power. Adding a backing washer during pop rivet installation was the cure.

[DaveO]

"I'm so glad we had this little chat." Off to get backing washers!

Thanks, Jakeru~