Cold Cracks
Cold Cracks
... And it sounds like I'll be avoiding a boat with wooden gunnels at all costs...
I wouldn’t necessarily exclude wood gunwales Royalex canoe s from your search. Wood gunwales have both aesthetic and practical values.
All of the cold cracked canoes I have seen 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.
So it isn’t just the cold, and it isn’t every canoe. The actual “why” is more of a mystery.
Back when I had deeper connections to various canoe manufacturers I offered to perform an experiment; I had plenty of wood gunwale scrap in the shop, and access to -20c, -80c and -150c freezer space. And liquid nitrogen. I suggested that if I had some test pieces of RX material I could screw together pieces of inwale and outwale and do some freeze/thaw experiments at different temperatures and different rates of temperature change.
Since no one in the business seems to know exactly why cold cracks occur, aside from the combination of cold temps, RX and (almost always) wood gunwales, I was surprised that no one was interested in trying to find out why.
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 know the cause, or not want to find out?
Cracks in Royalex CAN be fixed. They are not a manufacturing defect, rather as Ted indicated, operator error.
I believe that beyond the RX/wood gunwale combination the root cause may in fact be a 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 10 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. One of my test paddlers famously exclaimed that the canoe “shook more than Katherine Hepburn on an acid trip”. When I reported this to the manufacturer they admitted having had problems with their oven at the time that particular boat was manufactured. (Fortunately it was a vinyl gunwale canoe – it never cold cracked, but it remained inflatable floppy)
My suspicion is that cold cracks are the result of improper temperatures during the manufacturing process. Not hot enough for long enough, or perhaps too hot/too long…who knows.
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 a manufacturing defect at could cause them to cold crack in the right conditions.