I have an old Mad River Teton that has seen many trips into the BWCA over 20+ years. She's a tank, built for stability and able to haul a heavy load. I got it as a blem at REI all those years ago. My question is that I believe as part of the blem the middle of the floor will flex upwards when there is not a pack or gear on both the front and back of the middle yoke bar. Not a huge issue but this makes an already tough canoe to paddle even tougher. Any ideas?

We call that oil canning.
Not much you can do about it. The bottom is not strong enough to prevent it from flexing.
Time to let her go and buy a new canoe. It's hard enough to propel ourselves with a paddle let alone a bathtub caoe making it harder.
Tom

I have the same problem with an old canoe. I don't take it on trips but like to have it for the lakes around me if we have visitors. I tried to prop the canoe by both the bow and stern end and put weights inside the middle. I left it like this in warm weather for a day and it worked, but the indent bounced back once I put it upside-down on a storage rack. One thought I had was trying to adhere some sort of rigid rib or "U-shaped" material to the outside of the canoe to support and keep the dent from reforming?

If you are thinking something on the outside of the canoe
How about a keel?

Another idea is to add a thwart
Then a support up from the bottom of the inside of the canoe to the additional thwart.

Just thinking

IdealTarHeel

We are at the point where we use a tow service, portage once, and basecamp for a week fishing the same lake. The old tub has got it done this long, may just keep on plugging along. I was hoping there was some easy fix but it doesn't seem like that is the case. Thank you.

Polyethylene boats don't have much rigidity, less than Royalex and composites, hence the oil canning. Many years ago Wenonah added a foam center rib on the inside of their whitewater canoes to stiffen things up which still allowed flex for rock impact, but these were primarily racing canoes. Additionally, for their tandem canoes they had spring loaded shock absorbers running from the center rib to the thwarts to further stiffen the added span of the longer tandem boats. If the oil canning is really bothering you, you might try just adding some type of strut (even a 1x1) between the hull and the center thwart for use when needed (e.g. an empty boat?). For long term use, you might see some additional wear on the outside hull opposite the strut. You could duck tape the strut(s) in as a test just to see if it might work--Wenonah showed that the principal is sound.

The local nature center has a large fleet of rental boats, mostly all Old Town products. Since Johnson Outdoors (subsidiary of SC Johnson) is headquartered here we get really good deals on their canoes and kayaks. Probably half the Discovery canoes and some of the kayaks have distorted bottoms. They are all stored outdoors year-round so that may contribute to the problem. They are all rentals so no one complains.

MReid: " If the oil canning is really bothering you, you might try just adding some type of strut (even a 1x1) between the hull and the center thwart for use when needed (e.g. an empty boat?).
"

Probably the cheapest quality canoes I have ever seen are the 1980’s Colman’s canoes. You know the ones, cheap plastic with a flat bottom. Their canoes were so cheap that they put an aluminum pole down the center of the bottom. To keep it from imploding. I think they even had that strut you mention going from the bottom up to the center thwart to keep the bottom from buckling. A real bad canoe.

Tom

tumblehome:Probably the cheapest quality canoes I have ever seen are the 1980’s Colman’s canoes. You know the ones, cheap plastic with a flat bottom. Their canoes were so cheap that they put an aluminum pole down the center of the bottom. To keep it from imploding. I think they even had that strut you mention going from the bottom up to the center thwart to keep the bottom from buckling. A real bad canoe.
Tom
"

True but Wenonahs were pretty much state of the art at the time, and were winning a lot of races. Since then they just added additional layers of fabric for stiffening, and got out of the downriver racing market.

MReid: "

tumblehome:Probably the cheapest quality canoes I have ever seen are the 1980’s Colman’s canoes. You know the ones, cheap plastic with a flat bottom. Their canoes were so cheap that they put an aluminum pole down the center of the bottom. To keep it from imploding. I think they even had that strut you mention going from the bottom up to the center thwart to keep the bottom from buckling. A real bad canoe.
Tom
"

True but Wenonahs were pretty much state of the art at the time, and were winning a lot of races. Since then they just added additional layers of fabric for stiffening, and got out of the downriver racing market. "

I’m just having fun. Wenonah went on to improve their canoes. Coleman canoes were just cheap junk and they knew that. They were not trying to make any sort of improvement to their canoes. It was all about cost and comfort on a calm lake and a buyer with no knowledge of canoes and a flat pocket book. A little wave action and you flipped right out of it.

I had one of those coleman's. Somehow managed to take it from Lake One all the way to Alice Lake and back without flipping. Was a very nerve-wracking trip with that piece of junk. Sold it within weeks of returning home.