Fixing Cold Cracks

[dougd]

I am once again dealing with fixing cold cracks in a free boat, Mad River ME and I have a Mad River Explorer, free, coming to me with cold cracks. I have fixed these in the past and know how to do it the way I do it but would like to hear from others of the steps they went through to bond the edges up. I do know the way I did it to fix the boat (I sold it and know the owner) with the cracks is still going strong today. Just looking for what other ways folks fix these.

dougd

 

[dogbrain]

Hi Doug. I start by drilling a hole at the end of the crack. Then I drill 2 holes up where the gunwales were on either side of the crack and put in a cable tie to hold the crack together. Below the cable tie I use a sharp chisel and make a “v” on the inside following the crack all the way. . I go through the foam layer until I see gray. After flame treatment I fill the crack with the thickened g flex. After it cures I do the same to the outside and the area on the inside where the cable tie was, filling those holes too.

For added strength I put a strip of 4oz glass over the repaired crack inside and out using regular gflex, or I may have used regularcwest systems or raka epoxy. Then I just try to match and paint over the top.

Mark

 

[Canotrouge]

I do similar as Mark, but I do both side of the crack at the same time.. Just G=Flex for plastic boat and done, no glass or anything else! I'fixe lots of them, one is our caption and that boat sees a lot fo hard use and never had a crack open or fail!!

I have a MadRiver guide that I got for free that have some of the longest cold cracks I ever seen.... I'll try and get to it over the winter. I bought Gflex by the pail for that job!

 

[recped]

Not a cold crack but I rammed my Explorer into a giant boulder and cracked both gunnels, besides the expected creases there was about a 6" (clean) crack running down from where the gunnel cracked the worst. I had the gunnels replaced, the guy who did it just filled the crack with some unknown type of epoxy, no patches. While I haven't used the boat much since it seemed fine for the few trips I did.

 

[Robin]

I went to see a MR Explorer for sale once, the owner didn't even know about the cold crack we found and I got it for dirt cheap, maybe what it would cost to drop it at the local dump. I did the G Flex thing and added some new beefy ash gunnels. Nothing fancy, actually pretty rough, but I sold it dirt cheap to a young couple. They where happy, I had some fun and covered my expenses and an old canoe got a new lease on life. G Flex, it held up to a rubber hammer test.

 

[pblanc]

I do something similar to what dogbrain described with a few important differences. I have never found it necessary to try to pull the edges of the crack together. If the gunwales are still on, they will hold the edges of the crack in the correct position. You do not want the edges of the crack tightly opposed to each other. You want a small gap between the edges of the crack that the rather viscous G Flex epoxy can get into.

Rather than gutter out just the inside of the crack, I gutter out both the inside and the outside at roughly a 45 degree bevel half way through the thickness of the hull on both sides. This leaves a large bonding surface for the epoxy on both sides of the crack. In order to be sure there is a little space between the edges of the crack, I will usually drill a few closely-spaced small holes to allow a bare hacksaw blade to be introduced into the crack and run up and down its length to make a narrow gap. A Dremel tool with an appropriately sized and shaped diamond bit works well for beveling out the crack.

For bonding cracks, I thicken the G Flex epoxy moderately with colloidal silica powder (cab-o-sil) to create an "epoxy glue". I cover the crack on the outside with clear plastic packing tape to contain the epoxy, then prop the boat on its side and fill the inside of the crack. This often requires multiple applications as the epoxy works its way into the interstices of the exposed foam core. I then repeat the process on the outside of the crack. Any epoxy overfill can be sanded off flush before painting.

Although flame oxidation preparation does enhance the bond strength of G Flex to ABS according the West System's tests, a pretty good bond can be achieved without pre-oxidation treatment. This is contrary to polyethylene, to which G Flex bonds very poorly without pre-treatment. If one is going to use flame oxidation on cold cracks, extreme caution is necessary because any exposed foam core can melt very quickly even with very transient exposure to a propane torch flame.

If the crack is very extensive I will back up the repair with an interior strip of fiberglass or aramid, bonded with G Flex, but I have repaired cold cracks without reinforcement using this method and they have held up very well.

Here is an article from West Systems that some might find helpful:

http://www.epoxyworks.com/index.php/repairing-a-royalex-canoe-with-gflex-epoxy/

 

[Guest]

I believe that DougD is now the king of cold crack repair. Once the ME and Explorer have been repaired how many cold cracked canoes will that be?

Interesting that the Explorer had always been stored inside a (unheated) shed or garage. That busts the possible explanation that sunlight, rapidly warming the night frozen hull, causes expansion resulting in cold cracks.

TLDR: I have been curious about cold crack causes for 20 years, missed my chance to experimentally induce RX cold cracks, and still hold with the same theory; I believe that cold cracks result from an invisible manufacturing defect.

(Reprised & edited from a long ago post)
The actual “why” of cold cracks is a mystery. All of the cold cracked canoes I have seen in person or worked on have been residents of the mid-Atlantic region. It gets cold here, but nothing like further north, so the actual degree of cold may not be that much of a factor. And plenty of folks in the northcountry store their wood gunwale RX boats outside or in unheated areas, without backing out the screws and without problems.

I have seen an old local vinyl gunwale Explorer cold crack from each and every drilled hole for float bag lacing. Seen photos of a newer, aluminum gunwaled R-lite Nova Craft that cold cracked at the rivets for several years in a row. Royalex Light/R-84/R-lite canoes may be particularly over-represented, in numbers beyond their share of the ABS market, at least in northern storage.

The “cold” part is correct; I have never heard of a Florida RX canoe cold cracking, and there are a lot of Mohawk R-84 boats down that way. But it isn’t just intense cold or rapid temperature changes; I have stored at least 20 different Royalex canoes on an outside racks over the years and live in a weird micro-climate that may see the teens F at night, bright sunny and 50 the next day. Never had a cold crack (knocks wood).

So it’s a crapshoot; it isn’t every canoe, and it isn’t just wood gunwales & screws. Nor, apparently, warm sun on icy hull rapid expansion.

Why would some few RX canoes cold crack and many others, same make and model, stored in the same conditions, endure cold winters without any problem? And why would the manufacturers not have identified and eliminated the cause with a material used for 40 years by dozens of companies to produce tens of thousands of Royalex canoes? (I wonder if there is an estimate for the total number of RX canoes made?)

I am convinced that cold cracks are the result of an invisible manufacturing defect.

“Royalex® sheets are custom-made in a process that combines sheets of vinyl, ABS, and foam and then vulcanizes them together. The Royalex® sheet starts out as a flat sheet, which is then thermo-formed. During heating, the core expands, forming closed-cell flotation within the hull. At the proper temperature, the sheet is removed and placed on a platform, the mold is lowered on top of it, and the sheet is vacuum-drawn into the hull shape.”

I think the important phrases are “during heating, the core expands” and “at proper temperature”. I had a Royalex canoe in the shop years ago in which “at proper temperature” was not achieved; I suspect that the foam core never expanded sufficiently, and the hull bottom had all the rigidity of an inflatable.

I had paddled that same make/model RX before, and the two hulls were nothing alike. When I reported this to the manufacturer they admitted that, subsequent to a move they were having had problems with their oven at the time that particular boat was manufactured. That was possibly revealing.

My suspicion is that cold cracks are the result of improper time/temperatures during the manufacturing process. Not hot enough for long enough, or perhaps too hot/too long…who knows. Once it pops formed from the oven who the hell knows how the inside sandwich set up?

If that’s the case I can understand why Royalex canoe manufacturers would prefer not to know, or at least not admit that they know the cause. It’s easier to CYA by suggesting backing out or removing gunwale screws than to admit that a certain small percentage of RX hulls might have an invisible manufacturing defect at could cause them to cold crack, some even at lacing holes or pop rivets, under the right conditions.

About “Not want to know”; back when I had manufacturer connections I had daily access to a laboratory freezer farm with -80C and -20C freezers. And liquid nitrogen, and ovens and incubators and autoclaves. I offered a couple of manufacturers to run test pieces of RX, after screwing on lengths of ash inwale/outwale, through the gauntlet to see what it took to induce cold cracks.

Zero manufacturer interest. I shoulda bought a $50 RX derelict, cut it up and performed that experiment on my own when I had access to torture test equipment. I still want to know why cold cracks occur, and still think it is a solvable mystery.

 

[PaddlingPitt]

A little story for your consideration Our Mad River Explorer canoe had wooden gunwales, and a Royalex, plastic hull. My understanding is that plastic and wood expand and contract at different rates during times of warming and cooling. That didn’t make much difference when Kathleen and I lived on the west coast, where temperatures didn’t get all that cold. In Preeceville, however, winter temperatures usually fall at least on some of the days, to -40 degrees. That’s cold. One has to be aware of differential expansion and contraction rates.

I had read that to prepare for cold winters, one is supposed to loosen the screws that attach the wooden gunwales to the plastic hull. That way, the hull and gunwales can expand and contract at their own rates. Otherwise, severe cracks in the hull will almost certainly greet the once-proud canoe owner in the spring.

We moved to Preeceville in the fall of 2008. I loosened the gunwale screws at the beginning of winter in 2008. I loosened the gunwale screws at the beginning of winter in 2009. In the fall of 2010, I put the Mad River Explorer in the storage shed, and said to myself that I would loosen the screws later. I don’t know why I said that. It only takes about five minutes. But I would have had to walk a couple hundred metres (yards) each way to get my portable drill. I didn’t want to take the time right then. I would do it later.

Well, later never came. I got busy doing something else. I didn’t loosen the gunwale screws. In the spring of 2011, I slid back the door to the canoe storage shed, and literally staggered from the horrific sight. I started counting. Thirty-seven cracks all the way through the hull of my beloved Mad River Explorer.

 

[Black_Fly]

These cracks occur simply from the cold?

 

[goonstroke]

These cracks occur simply from the cold?

Yes. The coefficient of thermal expansion of wood is "not much" and that of ABS plastic is "a lot". I think most Mad River boats with royalex hulls and wooden rails have a warning sticker, but still, it's always seemed like madness to me. Like selling a car with plain water in the radiator and saying "oh, around Thanksgiving you might want to do something, if you remember..."

 

[PaddlingPitt]

I wish I had joined this CT site before I had the problem with cold cracks in the hull of my canoe. I didn't know what to do. I went on the internet a found a video where two guys were paddling a tandem Mad River with cold cracks in the hull. They had repaired them with Kevlar cloth. So, I sent away for a bunch of Kevlar cloth and Cold Cure, a two-part epoxy. I spent most of a day affixing the Kevlar cloth, inside and out, to all 37 cracks in the hull. In my opinion, the Mad River Explorer, although not as good as new, was just as seaworthy, lake-worthy or river-worthy as before. The boat didn't look as nice as it did before, though.

Anyway, after the job was completed, I returned to the house to boast of my success to Kathleen, knowing that she would be very impressed. “I can’t trust that boat anymore Michael. You say it had thirty-seven cracks all the way through the hull. What if it breaks while we’re on a wilderness canoe trip?”

“But it won’t break. It’s just as strong as before. Maybe even stronger. I put Kevlar cloth on the inside and the outside of every crack.”

“I don’t like it. I don’t want to take a chance.”

There you have it. Kathleen wasn’t happy. I had no choice. I had to buy another canoe. I called up the primary canoe store in Saskatchewan, Fresh Air Experience, with outlets in both Saskatoon and Regina. “I’d like to buy a sixteen foot Royalex Mad River Explorer, with wooden gunwales.”

“We don’t carry Mad River canoes anymore.”

“Well, I need a sixteen foot canoe. What do you have?”

“We have a sixteen foot Royalex Wenonah Prospector with vinyl gunwales in stock. Would you like that?”

I hemmed and hawed for a moment. I loved Mad River Explorers. I’ve owned two in my life. I couldn’t be changing brands now. But I needed a canoe, and soon. We were planning to paddle to Grey Owl’s cabin, in Prince Albert National Park in July, to celebrate our 30th wedding anniversary. I needed a canoe. I drove three hours to Regina the next day and picked up the Wenonah, with
vinyl gunwales. In the seven winters since then, we have suffered no cold cracks in the Wenonah. When we moved to Preeceville, we also brought our Dagger Rival and our Mohawk XL13. Both of these boats had vinyl gunwales. They never suffered any cold cracks. I like the look of wooden gunwales, but they are more work to maintain. And you gotta remember to loosen the gunwale screws.

 

[Guest]

Mad River FAQ on Cold Cracks

https://www.madrivercanoe.com/us/experience/faq/content/cold-cracks

Some interesting stuff there, including:

Cold cracked hulls are actually quite rare (well less than ½ of 1% of Royalex hulls in existence) contrary to the amount of concern the problem receives amongst the paddling community. There are literally thousands of Royalex canoes that successfully winter over year after year in the northern United States and Canada without any problem.

There's no such thing as a predictable threshold of 10o or 15o that will result in a cold crack. Nor can we specify that “X” temperature for “X” number of days will result in a cold crack.
We've had seasons when we've received reports of hulls cracking as far south as North Carolina while at the same time not hearing of any problems in Ontario or Maine. We've also heard of one person finding his boat cold-cracked while his neighbor, who stored his identical boat in a very similar manner did not have the problem. We've run into boats that cold crack the first winter out and others who haven't cold cracked in 25 years.

Synthetic gunwales are less prone than wood but it is certainly not unheard of for a canoe with synthetic gunwales to cold crack. Aluminum gunwales are probably a bit more susceptible to contributing to a cold crack than vinyl, particularly if a rapid drop in temperatures occurs. In such a scenario, the temperature impact on the hull causes the hull to shrink faster than the aluminum responds and the speed of the shrink can result in a cold crack. Cold cracks are least frequent in canoes with vinyl gunwales as the shrinkage coefficient of the gunwale is consistent with that of Royalex

I notice that MRC now recommends actually removing (not just backing out) all of the screws except for a few in the center:

We recommend removing all screws from each gunwale except the 3 centered over the portage yoke. This is also a great opportunity to freshen up the oil on your gunwales, particularly on the side of the gunwale that rests against the hull.

After a few winters of that it seems to me that repeatedly reinstalled screws would start to produce loosy-goosey screw holes.

I still believe that all evidence (see above reports) point to a hidden manufacturing defect, likely incorrect oven time/temps and improper foam core expansion.

 

[PaddlingPitt]

Interesting information, Mike. You might remember my Trip Reports when Kathleen and I wintered north of the Arctic Circle, and then paddled four weeks down the Anderson River after break up in mid-June. We took our MR Explorer to the cabin with us, and I completely removed all the screws from the gunwales. The canoe sat outside, and didn’t suffer any cold cracks.

Our first two winters in Preeceville, there were no cold cracks, which occurred in the third winter, when I forgot to loosen the screws. In all subsequent seven winters I have loosened the screws, and have had no more cold cracking. This sequence suggests to me that my particular wood gunwale/RX combination, with intact screws, caused the problem.

It does seem from your data above, though, that manufacturing defects could account for some cold cracking.

I wish I hadn’t forgotten to remove those screws. We don’t use the MR much anymore. With all those Kevlar patches it’s somewhat ugly. It’s also heavier and unbalanced because of the asymmetrical distribution of the patches. Every once in a while I trundle up to the barn to visit, and to grieve. I could tell myself that it was a manufacturing defect, and that it wasn’t my fault. I would like to believe that. But.......