Structural Failures

[BWB]

An interesting discussion of relative strength of materials in another thread has me curious. Has anyone experienced structural failure of the strip/epoxy/glass structure in service? Let's leave aside simple impact punctures for the moment. I'm curious about stress failures and how they occurred. Along the planking seams? Where in the boat? That sort of thing.

[Rick in Pender Harbour]

I have two cosine wherries entering their fourth year as rental boats, stored outside and used by all types of groups. My experience has been that they are more vulnerable when they are being transferred or unattended at the dock than they are in service. Total damage is a stress crack along the bilge of one boat, and a hole and damage to the keel as a result of the boat flying through the air and hitting the dock in a severe windstorm. The clients have managed to break the pins off two sets of bronze oarlocks, but nobody has damaged a boat out in the harbour. I am refinishing the boats and repairing the hole for another season.

rgds

Rick

[Tom in MN]

I have built 7-8 strip canoes and currently own three that have been in service for some time. I use them in many different environments, but not that much whitewater, which is the real test of any canoe. I have never had a structural failure of any kind in the hull, gunnels, etc. I have had a seat break but that is a different story. I did hit a rock one time in my 16' Whitewater that nearly threw me and my two sons out of the canoe. I was suprised that water did not come rushing through a hole in the canoe, but since it didn't, I just figured we would end the trip and I would cringe at the damage when I flipped it over. To my suprise, I could hardly even tell where we hit the rock, except for a small white mark "ding" in the epoxy. I build all my boats with a single layer of 6 Oz. cloth in and out. I would say the biggest issues are rock "gouges" that take a chunk out of the hull but are easily filled and patched over. Woodstip canoes are incredibly durable if you ask me, and when you do have an issue, fairly easily repaired as well.

[AlanWS]

Back when people used polyester resin rather than epoxy, the most common failure was delamination of the glass from the wood surface in spots. It's more common on the inside of the hull where flexing can tend to pull the glass away from the wood. This severely weakens the hull, and if it's not repaired, serious damage can result on impact. If repaired, it's plenty strong. Such delamination is rarer with epoxy, but deserves prompt attention.

I saw a canoe that had been damaged by flagrant misuse. While being pulled by a motorboat using a rope tied to the gunwale it capsized. With the boat full of about a ton of water (literally), it was pulled at high speed until the walnut gunwale was broken and torn off. The hull was undamaged: with new gunwales it's in good shape now.