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  How to fix "oil canning"???
  Posted by: waterbug on Jun-05-08 12:38 PM (EST)
   Category: Kayaks 

I looked at a nice plastic Eclipse....about 9 years old...

It was stored on its side (good...) but it has dents in the hull where it was tied into a stacker bar. I have heard this referred to as "oil canning"...

How does one get the dents out? Any ideas would be appreciated....

WaterBug


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Messages in this Topic

 

  Dents are Dents...
  Posted by: grayhawk on Jun-05-08 1:16 PM (EST)
"Oil Canning" is different.
 
 
  Greyak is Right
  Posted by: old_user on Jun-05-08 1:55 PM (EST)
That is not oil canning.

You might want to try using the weight of heavy sand bags placed on the convex side of the "dents" combined with a heat gun to see if you can restore some of the original shape.

HDPE is a viscoelsatic material. It creeps under constant load. Picture a piece of licorice. If you pull it hard it resists hard. If you pull it slowly and gently it will stretch.

The point is that if you try the sandbag trick, you will not see immediate results. You will want to let the load work over time. However, I think heat may accelerate the results.

 
 
  'Binka-Binka'
  Posted by: Jeffrey_Lee on Jun-05-08 2:06 PM (EST)
What grayhawk is so tersely saying is that the term oilcanning is often (mis?)used to mean permanent dents in a boat, which are in fact simply dents.

In canoe and kayaking circles, we typically use oilcanning to describe the active denting inward and outward of areas of the hull while underway, like on an old-time metal oil can that made a distinctive 'binka-binka' sound as you squeezed oil out. This is most often seen on wornout poly kayak hulls, usually just ahead of the seat, and even brand new superlightweight composite canoes.

*Interestingly, the sheet-metal industry makes no such distinction, and considers permanent waviness in large sheets to be 'oilcanning':
http://tinyurl.com/5gka2f

Regardless of such lexigraphic distinctions, you can remove such permanent dents from a poly kayak using a variety of methods of applying heat (hot-water-soaked towels, heat lamps, etc.) and pressure (bricks, wooden clamps or wedges) to gently soften the plastic, reform it, and let it cool in its proper place before removing the forms. I have a pretty comprehensive write-up on it at home, so will try to add it later.

Delphinus
http://www.AquaDynology.com
 
 
  Paddle the dents out.
  Posted by: string on Jun-05-08 2:24 PM (EST)
 
 
  had one with significant dents
  Posted by: Brazilbrasil on Jun-05-08 2:34 PM (EST)
-- Last Updated: Jun-05-08 3:59 PM EST --

right in front of the seat and I got a couple of those clamps that can convert to stretchers and placed two pieces of 2 inch wide and about 18 inches long on either side of the keel line and placed a small board on top of them. another board under the thigh braces and the stretcher in place to push the hull back out into shape.

Next, a propane heater underneath the boat about a foot and a half away and slowly heat the hull to hot to the touch and you can use a heat gun inside to try and match the outside hull temperature. When it heats up stretch the hull out to original shape and let it sit there for about 30 minutes (I never let the plastic get over 190 degrees) Then turn the heat off and come back tomorrow.

Note you might have to do this a couple of times if that plastic has been dented or deformed for a long time.

your mileage may vary



paul

 
 
  Careful with the heat
  Posted by: booztalkin on Jun-05-08 4:20 PM (EST)
My experience trying to reshape a hull with heat was not so successful. It is very difficult to control the heating so that the area you want reshaped heats evenly, and the properties of the material make it sort of all or nothing. If it doesn't get hot enough, no result. Too hot, the material becomes way too stretchy. Also, if there are imperfections in the hull, under heat that area will behave differently than the surrounding areas. The parts of the hull that get hot, and that you don't want to change, may obey the law of gravity and sag.

My experience was with a royalex canoe, so fundamentally different than a plastic kayak. But based on Brazil's 190 degree target temperature, it sounds like there are similarities. I found a source that said the melting point of royalex was 221 degrees. Nothing much happens at 190. Between 200 and 210, things get interesting and you have the ability to change the shape of the hull. But as you approach the melting point, things can get out of hand if you don't have the ability to keep the heat uniform and control the shape you want in all dimensions. I got one area too hot and caused a bubble that is now a permanent feature of the hull.

I'm not saying you can't do it, just that it's not something to casually try, and you can have problems. In my case, I wish I had just accepted the oil-canning and saved myself a lot of time and effort.

Good luck with your dents or oil-cans, as they may be.

~~Chip
 
 
  maybe I am just not aggressive enough
  Posted by: Brazilbrasil on Jun-06-08 12:30 PM (EST)
with the temperature as I have had to do this a couple of times and I find that that area is very easily bent back into its original "memory" of being dented. A quick stretch with that stretching clamp and it is back in shape. Perhaps I shoudl have gone up in temperature just a bit more and then tried cooling it more rapidly (bucket of ice water maybe?) to get it to forget the old memory and stay with the new?

dunno. will agree that it is not a casual fix and that extreme care shoudl be taken.

Paul
 
 
  bricks!
  Posted by: old_user on Jun-06-08 1:45 PM (EST)
I have an older rotomolded sea kayak that occasionally gets dents in it from being on the roof racks. To fix the dents, I put the kayak on the ground, on top of a brick at either end so that the middle is off the ground by an inch or two. Then in the middle, where the dents are, I put bricks inside the kayak, on top of the dents. Then I leave the boat in the sun, after a few warm days the dents are gone. They come back as soon as the boat is left on the roof racks in the hot sun too long, but they come out each time I use the bricks. The engineers and scientists can tell me if I'm doing any sort of weird damage to the boat by doing this every few months, but for me the bottom line is that the dents come out and the boat still floats and that's all I care about. :) :) :)
Susan
www.pennkayaker.com/ladyjustice
 

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