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Posted by DonTyson 
July 28, 2019 01:51PM
Reading and tinkering over the years I discovered the term and concept of oil-canning as it pertains to flat bottom boats. Is this a problem with a plywood drift-boat? While the cure is easy, I’m wondering if it is ever an issue?

Easton, Pa
Re: Oil-canning
July 28, 2019 06:23PM
Oil-canning can be a problem. Honky Dories built with 3/8" plywood bottoms will oil can a little, if you don't use enough glass. At which point you realize you could have used 1/2" plywood and a bit less glass. Is one better than the other? That's not clear.

Molded fiberglass boats that oil can a lot are total pain in the butt. Oil canning creates drag and slows the boat down. Most of those boats also tend to flex at the gunwale some, when you pull hard on the oars. That's lost effort. You have to work hard to bend the boat BEFORE it starts to move.

Severe oil canning, usually in molded fiberglass boats, often makes a low-frequency boom each time the bottom pops up or down. That's got to be bad for fishing.
Re: Oil-canning
July 28, 2019 09:33PM
Well one of the famous designers/authors, Bolger, Payson, Hankinson or Reule Parker wrote about this. I tried their solution on one of my small boats. It was as follows; when bending your bottom panels onto the chine add a quarter or so inch to the centerline of your station frames and bend the panel on. Apparently a small thickness sheet of ply can be coaxed to bend both ways ( in a cupped way) just enough to tension it against oil-caning.It seemed to work for me on a very small boat and I wondered if it has been tried by any of you on this site.
Re: Oil-canning
July 29, 2019 12:08AM
Interesting. I've wondered about warping the bottom some for years, not because of oil canning but because a slightly pooched down centerline, down the middle of the bottom panel, might make the boat track better. It might not. It's just something I've wondered about.

My last few boats have had 3/4" Plascore bottoms and have not oil canned at all. Most wood fiberglass bottoms don't either. The only case I know of is the HD (with its 56" inch bottom) when and only when it's built with 3/8" inch plywood for the bottom. Which you can fix in a variety of ways.
Re: Oil-canning
July 29, 2019 12:12AM
You have a captive audience if you can find the time to relay how you might fix it on the HD.
Re: Oil-canning
July 29, 2019 12:09PM
The HD doesn't need fixing if you use 1/2" plywood instead of 3/8" or if you use (this is the preferred method) 3/4" or 1" Plascore.

If you do build and HD with a 3/8" plywood bottom added glass will stiffen it up, perhaps 4 or 5 layers 10oz outside and 3 layers inside. That's expensive and it doesn't really make sense. But it works.

For a Plascore layup (that's expensive too) I use something like 4 layers 3.5oz outside and two layers inside. That's a minimal layup for Plascore but it works for me. I use 3.5oz only because it was on sale as a 'discontinued fabric and I bought a whole roll for approximately half the normal price. i've been using it for everything ever since.

I like to build (boats for me, not boats for sale to customers, which I haven't done in approximately 800 years) with a minimal layup because I tend to turn the boat over and add a new layer every four or five years. So a minimal layup is a good place to start.

That's the way to buy fabric. Call RAKA. Tell them what you are building. Ask them if anything is on sale.
Re: Oil-canning
July 29, 2019 12:22PM
I understand. But is that the only way you have to fix it? I was looking for a 'fix' for boats that do have an oil-canning as a problem. Perhaps this is so little of a problem in drift boats due to the excessive fore and aft rocker. Well, if it ain't broke don't fix it. I am pretty sure that I first read about this phenomenon in Small Boat Journal in regards to Phil Bolgers Sneakeasy, a very different boat. Once again "if it ain't broke don't fix it".
Re: Oil-canning
July 29, 2019 12:23PM
I built the first HD in 1986 as an experiment with end grain balsa wood.

End grain balsa turned out to be fine for anything above the water line but not for the bottom panel. After ten years that bottom was saturated with moisture. A complete disaster.

In I think 1998 I taped Visqueen to the inside bottom. Put carefully cut and fitted large chunks of 2" inch foundation foam on top of the visqueen. Put side to side 2x4s flat on top of the foam and then screwed through the side of the boat into the ends of the 2x4s to hold the visqueen in place.

Then I turned the boat over and rented the smallest water feed concrete saw they had and cut the wet balsa-core bottom off and replaced it with 3/8" plywood, which was also an experiment. It oil canned some. Not a lot. So I fixed that by adding glass and dry storage lockers. I never used 3/8" plywood for a bottom panel again. Then Plascore came along.

I've built one all Plascore boat and friends (Larry Hedrick) has too. Larry built an all Plascore HD he has taken down the Grand Canyon several times. I'm not sure all Plascore does or adds much. It is great for the bottom panel. 1/4" Meranti Hydrotech glassed on both sides is fine for side panels and dry storage lockers. 3/8" Meranti Hydrotech is fine for a deck.

I try never to build the same way twice. I'm a design shark. I have to keep swimming forward with new ideas or I asphyxiate and die.

I've made a zillion mistakes and failed experiments. They always lead to more better in the long run.
Re: Oil-canning
July 29, 2019 12:40PM
You're a designer at heart. And you get 100 "at-a-boys", remembering that it takes a thousand "at-a-boys" to erase one Oh-shi_!

The spirit of the oil canning comments I read were along the line that it would take allot of weight in fiberglass and resin to get rid of the problem and that simple tweaking could have solved it with no additional weight added.
When I tried it I played out the station frames as directed, layed the bottom panel over it and traced the outline 1/4" over sized. Before I fastened it down I put a little block of wood in the middle of each station. I think they were 1x1" x 1/4 luan. anyway the bottom still fastened up nicely but the bottom was tweaked a bit. Seemed stiffer to me. It was a 10' flat bottom rowboat with 1/4" bottom.
Re: Oil-canning
July 29, 2019 12:48PM
I'd like to see you play around with round boat hulls to be used as one-man drift boats for small fast streams. There have recently been some round one man electric-powered boats featured on youtube but they're not drift boats.
Re: Oil-canning
July 29, 2019 12:49PM
RE> plywood vs Plascore bottom panels

On tailwater rivers like Montana's Big Horn or Missouri below Helena or the Delaware 1/2" plywood is fine.

Rivers more like the Yellowstone or Madison are different. Rowing the Madison all summer is a bit like turning your boat upside down and practicing drums with a sledge hammer. For those rivers Plascore pays for itself. The fiberglass skin will get dinged cut and split. With plywood you have to patch it immediately. With Plascore you can wait until January.
Re: Oil-canning
July 29, 2019 12:55PM
When Lewis and Clark headed West they used loooooong skinny dugout canoes they called Pirogues. They tipped over a lot.

On the trip back East the next year two guys got separated from the group on the Yellowstone and the Crows stole their horses in the middle of the night. So they shot two big bull bison and made Buffalo Boats, which were round wet skins lashed onto green willow branches. And then dried in the sun.

They couldn't believe how much better the Buffalo Boats were. They never tipped and you could go left or right as well hold steady. Long and skinny goes forward quickly but it's dangerously unstable. Wide and rounder is still nimble. And way more stable.

Post a link to your round boats. I'd like to see one.
Re: Oil-canning
July 29, 2019 01:05PM
Re: Oil-canning
July 29, 2019 01:34PM
Yes that is one of them. But for whitewater( something I know nothing about) you would need to lower the center of gravity allot. Many of the Native Americans used round boats for all-purpose work.
There are allot of small streams where these might work well where the longer boats might have issues with nimbleness. My my, these would certainly have oil-canning issues.
Anyway, since you’re retired and have absolutely nothing going on, lol, I thought you might work on it.
Its Monday morning, think you could have something by the weekend?

Re: Oil-canning
July 29, 2019 01:55PM

For white water you need a kayak. Or a dayak.
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