Manufacturers suggest that you loosen the gunwales at the ends of your wood-trimmed Royalex canoe before you store it for the winter. This is supposed to prevent the Royalex from cold-cracking when the temperature drops. No one knows exactly why these cracks occur, but most believe that wood and Royalex contract at different rates–when temperatures drop, something has to give. Usually, it’s the Royalex.
Over the years, I’ve owned six wood-trimmed Royalex canoes, and until recently, I never had a problem. Then, last spring, disaster! A five-year-old solo canoe and a 10-year-old tandem model both developed serious cracks. What gives?
I store my wood-trimmed Royalex canoes in an unheated garage where winter temperatures sometimes reach 30 below zero. The last two Wisconsin winters have been fairly mild–temperatures have rarely gone much below zero. Why, after so many years of “bad winters and no problems,” did those canoes suddenly crack? I have some theories, but first, some observations:
I have never loosened the rails on any of my canoes, as advised by manufacturers. Instead, I keep the woodwork heavily oiled (Watco or Djeks Olay). I have long believed that ice is the culprit. For example, you put the boat away wet and water penetrates the dry wood, where it freezes and causes the wood to expand. Cracking follows. My policy has been to dry my boat, oil the woodwork, and uniformly tighten all screws before I store it away. Until recently, this practice has worked for me.
I’ve seen a lot of cracked Royalex canoes over the years. The cracks almost always develop near the ends, and in line with screw holes. Hmmm.
A canoeing friend who lives in Mountain Iron, Minnesota–where winters are bitterly cold!–owns an ancient (like 20 years old!) Royalex Mad River canoe. Herb stores the canoe in a shed and seldom tightens screws or oils the trim. Two years ago, he became concerned about cold-cracks, so–for the first time–he released the ends of the canoe. That winter the Mad River cracked just behind the released rails. Hmmm, again.
I have two 10-year-old canoes with fiberglass deck-plates that are screwed to the top of the rails. No problems.
THEORY When I repaired my damaged boats, I observed that the gunwale screws were very difficult to remove, which suggests that the wood (gunwales and fitted decks) had swelled. One theory is that the wood absorbs moisture (more so if the canoe is used in transitional weather, then put away wet) and expands. Expansion continues as the temperature drops and ice forms. Pressure on the screws causes cracks to develop in the surrounding Royalex. Or perhaps the Royalex simply contracts more than the screws. How else can one explain why the cracks almost always occur in line with screw holes?
This fall, I plan to remove the gunwale screws near the ends, then enlarge (with a bigger drill bit) the screw holes in the Royalex. Hopefully, this will eliminate future problems.
REPAIR THOSE CRACKS Fortunately, cold-cracks are easy to repair. Do it right and the fix may be stronger than the surrounding hull. Cosmetically, you won’t notice a thing.
Remove the rails near the break. Force open the crack with a thin-bladed putty knife and flow boatbuilding epoxy (not the five-minute type) into the tear. Remove the putty knife and wipe off the drips. That’s it, project complete.
For deep cracks: Same as above, but cover the crack with fiberglass on both sides. Be sure to sand off the outer vinyl layer of the ABS substrate so the glass will stick. For extra strength, use a layer of Kevlar inside the hull. Cover the Kevlar with fiberglass so you can later sand the edges. Sand, polish, and paint to match. Now you’re ready for an expedition!
Finally, it’s no secret that plastics age-harden and crack. You’ll add years to the life of your Royalex canoe if you religiously apply 303(tm) Protectant to the hull–inside and out.