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What are cold cracks?
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.
How common are cold cracks?
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. 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.
This is not to downplay the impact when it is your boat that cold cracks, but to provide perspective as to the frequency of occurrence.
At what temperature do cold cracks occur?
We know why the problem occurs, the bigger issue is there is no absolute way to predict when a hull will crack. 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. This is one of the most frustrating aspects of this issue, there's seemingly no rhyme or reason to it.
We also have sufficient data to indicate that a sudden and severe drop in temperatures such as might accompany the onset of a strong cold front can also be a significant cause of cold cracks. However, similar to the above, we have no set formula that specifies a drop of “X” degrees with an “X” amount of time will create cold cracks.
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.
Are certain types of gunwales more prone to cold cracking than others?
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.
One thing that is key to successfully wintering over a wood gunwaled royalex canoe is properly maintaining the gunwales with Gunwale Guard. Gunwale Guard seals against moisture penetration and retention and increases the elasticity of the wood. Dry (un-oiled) gunwales readily absorb and retain moisture which will then be subject to expanding when freezing.
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.
How can I prevent cold cracks?
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.
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.
Royalex Canoes with riveted Aluminum or vinyl Gunwales
With canoes with gunwales attached with rivets, there's not much to be done. If a strong cold front is predicted with significant and rapid temperature drop anticipated, you might be wise to throw some type of insulation over the canoe to slow down the impact of a severe temperature decrease. Quilted mover's blanket pads, old blankets, etc. all will help.
Royalex Canoes with square drive fasteners (such as Vinyl or IQ2 Gunwale systems)
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:
Royalex Canoes with IQ aluminum gunwales
The IQ gunwale is secured via square drive fasteners. Decks are secured by Phillips head screws.
Are cold cracks covered under warranty?
No. Cold cracks are caused by subjecting the hull material to stress beyond its design limitations and are thus excluded from warranty coverage.
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.
The facts that no correlations have been uncovered,that occurrences seem to be overwhelmingly random in nature, and that diligence in preparing a canoe for winter storage do reduce the incidence of cold cracks all give credence to the position that this is an endemic limitation in the material's ability to respond to temperature changes.
It is rare that a canoe will suffer cold cracks sufficient to render it unsafe to operate after repair. For this to be the case, there has to be a high number of cracks on each side and for opposing cracks to come within close proximity to one another. In the vast majority of cases, cold cracks are fully repairable and there is no compromise on the integrity of the hull.
Mad River Canoe's response to cold cracks has long been to assist the owner to get the boat back on the water. We don't think it fair that the owner should be left holding the nasty end of the stick all by themselves and will usually work with owners to provide necessary repair materials at a reduced cost, providing that photographic evidence indicates that the gunwales have been properly maintained. If the gunwales look to have been ignored from experience we know that this is definitely a major contributing factor to cold crack occurrence. This is also something that is obviously beyond Mad River's control and it follows that we will not take responsibility for correcting that circumstance or any results thereof.
How are cold cracks repaired?
In short, kevlar or fiberglass patches are placed on the inside of the canoe and embedded in epoxy adhesive. It is not a particularly complex process but can be a bit messy.