View topic - defn: Oil Canning

Can someone please define this for me... I've seen it in a number of posts and even manufacturer's sites but haven't found a definition yet.

Thanks.

It's the effect where a large, flat sheet of material tends to wow and buckle because it's not very rigid. I believe the origin is from the old style oil cans where the bottom was an 'almost flat' convex dome shape. You would push on the bottom and pop it in to force the oil out.

From a canoeing viewpoint, it refers to the (undesireable) property of a flat bottomed canoe to be too flexible, and ripple and wow in and out as the canoe passes over waves. Obviously not a problem in a loaded canoe, since the packs hold the bottom down. In theory, it makes the boat less streamlined or hydrodynamic because of this movement in the bottom.

Frankly, I think it's overrated as a problem, unless you're in a real performance boat, and paddling it unloaded. Even in an unloaded boat, I find the effect has an almost unnoticeable effect on speed. Perhaps I'm not a very sophisticated paddler.

It can be a little disconcerting visually, though.

I asked John Winters about this and he said he performed some experiments (on models) with radically deformed hulls (similar to an oilcanned canoe). He said he did not detect any changes in drag; most drag comes from the accumulation of scratches.

It definitely is disconcerting and I ended up fixing my ultra-light Quetico with West System and some glass to stiffen the hull.

Great summary. I would just that, in my experience, "oil canning" is most noticeable in an unloaded ABS (or similar) canoe with no keel-type structure.

To see it in spades, try an old ABS Blue Hole or Old Town Tripper canoe. With packs and gear, it all but disappears.

To see how it can be minimized, try a Mad River with a V-bottom.

Never heard of it in an aluminum, cedar strip, or fiberglass canoe. They are too rigid for any wobbling or flexing.

- James

Penny et al

Try pushing on the side of your washing machine or dryer or maybe the fridge door. Notice the way the thin metal sheet flexes or pops in? That is kind of what they mean by oil canning of the bottom of the canoe hull. A thicker or more rigid metal on your washing machine wouldn't do that - maybe yours doesn't. The same with a canoe, a more rigid hull maintains its shape. It is more common on flat bottom hulls as opposed to round bottomed hulls.

Thanks, folks, for your info.

I am fascinated at the comment that the changing shape of the hull has little or no effect on overall drag, though, whereas scratches do. I assume it has to do with the disruption in the linear flow caused by the scratches? Yuri_k, do you know how great an impact on the drag the scratches made? i.e., would it be a noticeable difference? We have a very beat up old Scott Tripper Kevlar (used to be a rental, it's filling a gap until we figure out exactly what type of canoeing we'll be concentrating on). SHould I seriously look at the outside hull smoothness?

Penny:

See this thread

Thanks all, for the insight!

I wouldn't freak out too much about scratches on your boat. In principle scratches add turbulence so increase drag. In practice the effect isn't huge and as the article on the link says turbulence is hard to avoid. The effect may be 5%...I'm guessing... but it's not a night and day difference. Probably worthwhile if you race long distance. Another tech article points out that the first three feet of the boat is most important since that's the only part where you might avoid turbulence. Oil canning occurs mid-boat. Fish change their hull shape and there is research around flexible skins for submarines. I just spent a lot of time polishing up my oldest scratched up boat and I really can't tell if it helped but it made me feel better for giving it some love.

https://www.fsc.com.au/wp-content/uploa ... bottom.pdf

Oil canning: In past times, Oil that you would want to squirt out of a narrow nozzle onto something would be put into a squat low and wide bottom metal can with a thin flexible pipe coming out of the top. the bottom of the can was thin and flexible. so when you gently pushed on the bottom it wold pop inward and make a clicking sound as it pushes a drop of two of oil out from the nozzle, then the bottom would pop back down to the original position. That flexible bottom motion up and down is "oil canning". Generally thought to be an undesirable characteristic of a cheaply made canoe hull.

First, I assume "oilcanned" means a canoe with a 'hogged' hull:
https://en.wikipedia.org/wiki/Hogging_and_sagging

While there may be no noticeable difference in drag with some oil-canning, it can have a negative effect on performance and the longevity of the hull material when extreme.

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My Nova Craft P16 in Royalex definitely oil cans when empty. No big deal as far as I'm concerned.