Another strip canoe delamination

[RickR]

Stripperguy’s saying that “every scar tells a story” is true for us and we now have a story that requires repair. We enjoyed a leisurely, lovely Moose River Bow Trip out of Jackman, ME 5/21-26/24. We almost cleared the ledge drop at Mosquito Rips unscathed, but the stern stem hit HARD as we exited. Hull inspection that night at camp showed nothing noteworthy on the exterior. The exterior layup is 6 oz E glass, and 5 inch waterline football plus 4 inch and 2 inch wide bias cut stem strips of 6 oz S glass. Back home, washing the canoe to put away, I noticed the interior glass around the stern stem was bubbled up. Remarkably, there was no water intrusion or wetting of the wood core. I suspected that I’d done a poor job of squeegeeing at wet out and that caused the failure. But all removed fiberglass (6 oz S glass) was covered with wood fiber, sometimes deeply.

I’m surprised that the damage is only to the interior, particularly considering that the location is probably the strongest, stiffest part of the hull. I guess I don’t need to understand it, just fix it.

 

[Alan Gage]

That must have been a heck of a hit.

I'm no expert but I think it's fairly common for damage to be worse on the interior in such situations. The exterior will be in compression and the interior in tension; and tension often fails first.

On my current build I'm a little worried how much the bottom might flex due to a pretty flat bottom design. For that reason my football layer will go on the inside for extra tension strength.

Glad it didn't affect the trip at all. Looks like you have it well in hand.

Alan

 

[memaquay]

As Alan mentioned, the interior layers often show the most damage. I had it happen on a large 18 1/2 foot canoe I built, the hull flexed upward on a very strong hit, and the interior glass split for about 18 inches. It was a worrisome paddle for the rest of the day, watching the split flex and gape, wondering if the exterior glass was about to split as well, but it held together until we hit the emergency extraction point. Same thing happened on the first Raven I built, although the damage was much smaller.

 

[Gamma1214]

As mentioned above, for max impact strength, the extra layer goes inside, for max abrasion resistance, it goes outside.

Still, it looks like it took a pretty good whack to do that and I'm glad the boat held up to it. Also looks like you've got the repairs well in hand and it's probably somewhat reassuring to see the wood fibers still adhered to the glass.

Will you attempt to fill the area with thickened epoxy before re-glassing it?

 

[RickR]

Will you attempt to fill the area with thickened epoxy before re-glassing it?

Yes. My thoughts are to level the rough wood surface with thickened epoxy, wet out a piece of 6 oz S glass slightly smaller than the raw wood margin to get back to height, and then apply another larger, overlapping layer of S glass to bond everything together.

I'd appreciate hearing other techniques/approaches though!

Rick

 

[Cruiser]

If that flap will lay back down, I think I would be tempted to use unthickened epoxy to saturate the area, tape it down and use something like a sand bag to add some pressure and leave that to set.

Scrape flat and then look at adding the patch, just my 2 cents

 

[RickR]

If that flap will lay back down, I think I would be tempted to use unthickened epoxy to saturate the area, tape it down and use something like a sand bag to add some pressure and leave that to set.

By the time I worked the bubbled glass back to a solid margin most of the pieces removed were quite small. It was a tight area to work in. The delamination in some areas extended beyond the bubbled glass. I'd cut at the edge of the bubble and sometimes find the adjacent area to be flat, tight, but free. That's where a lot of the small pieces came from. This condition was not obvious visually, but sound was a dead giveaway. Lightly tapping the hull told me when I'd gone far enough.