How long should ash gunnels and trim last on a new high grade canoe (such as a Hemlock) if it is stored inside and properly oiled on a regular basis?
or maybe two or three lifetimes.
of the possible areas of hidden rot. Every time you invert the canoe after getting water in it, water trickles down between the hull and the ends of the thwarts and also pools under the tips of the deck plates at the stems. If the inwales and outwales do not fit tightly against the hull, water can also get between the gunwale rails and the hull.
Water also follows along the machine screws that attach the thwarts and suspend the seats and can enter into the wood that way. Even good makers do not always seal the wood at the ends of the cut thwarts or after drilling holes for the seat and thwart hardware. I would bet that virtually none do anything to seal the wood that the gunwale screws penetrate.
For all its excellent properties, ash has a very open grain which unfortunately can allow moisture to soak in. Over time, the exposure to water causes the grain to open further exposing more and more wood to water and potential rot. The open end grain at the ends of the inwales, outwales, and thwarts is particularly susceptible to this type of progressive damage.
Although with proper care and storage the ash trim should last a very long time, with frequent use these areas of relatively unprotected wood can eventually sustain damage that is easy to overlook.
If your deck plates do not already have them, I would consider drilling holes at the tips of them as close to the hull as possible, to allow drainage of water that tends to collect there. Even with drainage holes, some moisture will remain, so you may want to take a dry towel to the undersides of the deck after use before you put the boat up. If you buy a new boat, I would suggest removing the thwarts and seats, then drilling the holes in the thwarts, seat hangers, and inwales slightly larger so that the hardware goes through without any friction. Then oil the cut ends of the thwarts, and the machine screw holes well. A pipe cleaner works fairly well to get oil into the screw holes.
I probably wouldn't remove the thwarts and seat(s) every time you oil the rails, but I would certainly consider doing so and reapplying oil to these areas once or twice a year, depending on use.
Unfortunately, penetrating oil finish is not that durable. Nowadays if I rerail a boat or have occasion to remove the gunwales for some reason, I will sand the inner faces of the outwales and outer faces of the inwales and seal the wood with a low viscosity penetrating epoxy, even if I plan to oil the visible faces.
Owned Curtis & Hemlock
For decades with no trouble by doing just as you stated.(Curtis was Hemlock forerunner). Unless your rails are CONTINUOUSLY wet you should have no problems.
Pblanc’s advice is sound though. If you are buying a new boat I would suggest removing thwarts and seats if you cannot reach the ends and put some oil on the ends as often they are not covered. If you are having Dave build one for you ask him to do it while constructing.