Builders' Forum |
|
| ↓ Scroll to Last Comment ↓ | Forum Guidelines | Builders' Forum |  RSS
|
Repairs to Delaminated Plywood in a Skerry
I’m currently renovating a Skerry, and I’ve encountered a badly delaminated section of plywood to each side of the center seat knee on the port side.
I suspect from the heaviness of the fillets and the discoloration there that the previous owner tried to repair the delamination by applying copious amounts of epoxy, without enough varnish afterwards. The plywood around the leading edge of the seat knee is tangibly soft.
My current plan is to detach the section in question from the strake below it, the seat knee, and the gunwale with a heat gun and a chisel, and saw the edges square on each side. I’ll then fit a new length of 6mm Okoume to the section by scarfing it to the solid plywood to each side, and attaching it to the strake below and the gunwale according to the instructions in the build guide.
I don’t have much confidence in my ability to plane or sand a decent bevel in the hull for an ordinary scarf, but I believe I can form a ‘staircase’ scarf as per Jim Trefethan’s book “Wooden Boat Renovation,” where he describes using a router to create interlocking rabbets to scarf the edges of a patch to the area to be repaired.
Does anyone with more experience (that is to say virtually everyone) have a better or more practical approach?
As a neophyte, I’d be happy to hear any advice or suggestions.
Thanks in advance!
2 replies:
RE: Repairs to Delaminated Plywood in a Skerry
H.,
That makes sense: on both sides there was clearly a lot of separation around the 'finger' joints and that seemed to be the epicenter. I mentioned the varnish issue because it looked to me like a lot of (now discolored and cloudy) epoxy was piled onto the area to try and seal off the area after the fact.
As it turns out, I got lucky while cutting out the delaminated portion. My initial cut around the obviously compromised (an area of ~ 5”H x 24”L, with the bottom adjacent to the strake below) needed to be extended out to the sides a bit to reach solid plywood, but it was solid top and bottom, so I’ll only need to patch a section along the bottom. Once I’d cleared all the filleting from the rabbet to the strake below I had a nice clean top surface, including a picture-perfect cross section of the epoxying of the seam. On a closer look, the crack along the top edge turned out to be mostly epoxy and varnish, and probably separated because it was the only solid point where the knee was still attached: once I removed the fillet from the knee, it closed right up.
In other good news, I tested the 6mm Okoume I’ll be using to make the patch, and bending it to match the curve of the area to be patched was a breeze.
So my next step will be to practice the ‘staircase’ scarf on some scrap plywood before scarfing the sides and top of my new window and a corresponding patch.
You're on point as to the fillets, and I'd planned on going over all of them as part of the post-repair epoxying/varnishing/painting.
I was really worried going into this, so appreciate the vote of confidence!
- D.W.
RE: Repairs to Delaminated Plywood in a Skerry
» Submitted by hspira - Sun, 8/6/23 » 12:00 PM
hi dwdeg,
saw your note above and though i could offer some comments.
first, if you have delamination/rotten wood, that is an issue of the wood not be encapsulated in epoxy...and subsequent water intrusion and rot....and not a varnish issue.
the area you describe, when a hull is flexed, has sort of a fulcrum which, overtime breaks/cracks, the joint/fillet between the knee and plank. the crack then become an area for water intrusion, which if not addressed immediately, leads to the situation you have.
your approach sounds reasonable. it might be made simpler if you simply butt jointed it and put a doubler behind your patch. while its not a 'artistic' it would probably not be particularly noticed.
i would also recommend a careful inspection of all your fillets (and every joint) looking for cracks....make this part of your annual getting the boat ready for the season ritual. Also ensure the boat is stored dry. marine ply can get wet and will not immediately fail. so what you are seeing is the result of extended time (probably years) of a minor issue not being addressed, eventually resulting in the problem you are now trying to fix.
h