Royalex is susceptible to shrinkage when exposed to freezing temperatures. A sheering fracture (cold cracking) is a potential hazard if you live in area with rapid fluctuation or freezing temperatures, particularly canoes with wooden gunwales.
Royalex is much more resistant to heat deformation than canoes made of polyethylene. Cold temperatures can pose a bigger threat. Royalex canoes can be susceptible to cold cracks due to hull contraction and expansion. Wooden railed canoes are more prone to this than those with synthetic gunwales. Most canoe manufacturers have taken steps to minimize the possibility of cold cracks and include tips on how to store your boat for the winter season in their owner's manuals. More information on cold cracks and repair can be found below.
Mad Frost Crack
Download: https://cinurl.com/2vF1Bf
Repair of dents and deep scratches involves filling with Royalex repair resin. Repair resin is a puttylike 2-part resin that cures to a hard finish. Some sanding will be required as well. Repairing tears or cracks requires multiple layers of Kevlar cloth laid in and covered by the repair resin. Fiberglass cloth can also be used but the inherent flexibility of Kevlar better matches that of Royalex. Structural repair is generally done on the interior of the hull.
Paddlers living in colder regions or in areas subject to rapid temperature fluctuations have learned that Royalex canoes can be subject to what are called cold cracks. Cold cracks occurred when temperatures reached the teens or lower and/or there was a rapid temperature swing of 20-30 degrees in a few hours. Royalex is an elastic material and will shrink or expand slightly due to temperature changes.
At colder temps, the material has a tendency to contract. When that contraction occurs at a different rate than that experienced by the gunwales, the hull could crack at the screws or rivets used to attach the gunwales. These cracks would often extend up to 8-10" down into the hull of the canoe. Contrary to most damage incurred by paddling, cold cracks can be identified by their vertical orientation. In severe cases, one could encounter a series of 6 to 8 or more cracks originating at a succession of attachment points. Royalex canoes with wooden gunwales were somewhat more susceptible to this problem than those with synthetic rails. As canoe manufacturers became aware of this problem, they took steps to reduce its occurrence.
Steps recommended for the user to take included backing out the screws in the ends of the boat as cold cracks tended to occur more frequently in these areas. Steps were also taken in the production of the boats to make this problem less likely and these precautions have appeared to have had an impact as incidents of cold cracks have diminished. Still, its possible to experience the problem or to find a canoe for sale with the problem. Indeed, if you are fortunate to find such a boat, you will often find a bargain as the damage looks worse than it is.
As cold cracks are found up near the gunwale, they're located in a less critical area than if they were found below the waterline. Repair consists of removing the gunwale, aligning the hull parts and reinforcing the interior hull with Royalex repair resin and cloth. Cosmetic repair of the hull exterior is accomplished by slightly widening the crack and filling with repair resin.
You may need to build a "jig" to reshape the canoe to its original form. This can be done with duct tape, cardboard, and wood as well as any other materials that come to mind if they'll do the trick. Be creative. If the damage is confined to one side of the boat, you can force out (or in) the damaged side by bracing temporary cross-members off the sound side of the boat. Run a line of rope or cord down the center of the boat from end to end and sight down the line to assist in making the boat as symmetrical side to side as possible. Gettinag the two sides of the crack to align can be trickier.
Any bracing or jig should be applied to the hull exterior since you'll be doing the repair primarily on the inside of the hull. Taping lengths of cardboard or thin bendable wood strips will often help the hull take its original "fair" curves or close to it. It can be challenging to conform the crack should it extend through the chines (where hull side transitions to bottom). Again, be creative. You can force a hull "out" by running a down brace from a thwart or yoke ending with a plywood or foam pad against the hull. If a thwart or yoke is not in proper position, make a temporary cross member and wedge it under the gunwale to anchor your down brace.
If you're faced with bringing in part of the hull to conform, it's a bit more challenging. It may sound counterproductive but you can drill two small holes close to the crack and run a line through them and up around a thwart or yoke and tension the line to conform the hull. In most cases the drilled holes will ultimately be covered by repair material so no further damage has really been done.
Royalex is sensitive to temperature. Simply put, Royalex will contract when exposed to cold temperatures. This material property is the cause of what are termed "cold cracks." Cold cracks are fractures of the material usually running perpendicular to the keel line of the canoe and terminating at a fastener along the gunwale line. A canoe can experience a single cold crack or show a series of roughly parallel cracks over a portion of the hull. The majority of cold cracks occur towards the ends of the canoe.
Cold cracks result when the hull contracts in opposition to the gunwales remaining stable or actually expanding (wooden gunwales with entrapped moisture). As the hull contracts in opposition to the gunwales, stress eventually builds up that results in a sheer tear in the hull material at the point of junction between gunwale and hull.
Cold cracked hulls are actually quite rare (well less than 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. Some years the numbers are worse than others but a "bad" year, still only results in reports of 20-25 canoes suffering cold cracks. Most years we get reports of no more than 10.
Another contributing factor to cold cracks is canoes being bumped or dropped in freezing temperatures and fracturing upon impact. It is best not to handle or move your canoes in such conditions. Wait for a better day.
Wood gunwaled canoes are the most prone to cold cracking. This is primarily due to the absorption of moisture in the wood rail which will then expand as it freezes, resulting in a gunwale that is actually growing while the hull is contracting. As you might expect have forces moving in opposition to one another is usually a good formula for failure.
We know properly oiled wood gunwales are effective in minimizing cold cracks simply because Mad River stored hundreds of Royalex canoes with wood rails throughout an awful lot of Vermont winters in an unheated warehouse with very, very few losses. Those canoes benefitted from a fresh and thorough coating of oil. As noted above, merely slapping on a coat of oil when putting your boat up is unlikely to do the trick and may actually increase the likelihood of a problem. Gunwales that have not been properly maintained need to be thoroughly dried before being re-oiled.
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. However, most vinyl gunwales have an aluminum insert to provide the necessary stiffness for paddling and in most cases, the gunwale is affixed to the hull via screws or rivets driven through the aluminum insert. Thus, it's certainly not impossible to find a vinyl railed canoe with a cold crack.
Almost 40 years of experience and a lot of hours and intelligence dedicated to the problem, not only by Mad River but also the manufacturer of Royalex as well as other canoe manufacturers, and no one has yet come up with a guaranteed way to prevent cold cracks, short of storing your canoe in a heated area. Fortunately, there are ways you can minimize the likelihood of cold cracks. These range from storing your boat in a heated space to removing or loosening some of the fasteners in the gunwale. The recommended process has been adopted from long experience of a Mad River dealer in northern Canada. He exclusively uses Royalex canoes with wood rails in his tripping business as the royalex provides the durability he needs and the wood gunwales are the only kind that can be repaired in the field. In 20+ years of experience the only hulls he has lost to cold cracks have been due to a rack collapsing and dropping canoes to the ground or a canoe being bumped in severe conditions.
Though less likely to suffer cold cracks than wood gunwales, if you live in regions that suffer prolonged severe cold or are prone to swift onset of cold fronts, it may be to your advantage to reduce stress on your hull by:
The manufacturer of Royalex does not warranty the material to the canoe molders for this issue. It is their position that it is a material limitation, not a material defect, that makes the material prone to cold cracks. Given all the studies and effort that has been dedicated over the year to solving this issue, that position is justified.
Mad River has logged and studied years of cold crack reports looking for any patterns that could be clues to potential solutions for this issue. We have analyzed reports to see if any specific Royalex sheet design has shown to be more prone to cold cracking than another and have never found any correlation in that regard. Nor have we found that Royalex produced during a specific time period was more prone to cracking than that from another time frame. 2ff7e9595c
Kommentare