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randii
10-19-2018, 01:30 PM
i started a thread over here: http://forums.sailinganarchy.com/index.php?/topic/203513-cockpit-coaming-repair/
... but in searching the web more to find my own answers, I think there's more wood and less 'glass here, so I'm asking here also, for broader experience.

I have a boat skinned with double-diagonal Okoume ply. Most of the boat is quite solid and rings true when thumped, but the cockpit edge (coaming?) is separated in places, and that's one of the first pieces I'd like to correct. There's delamination in places along the first inch down, and I could cut this away and get down to properly laminated wood, and build back up to level (original construction created an uneven/unlevel arc in the edge, and cutting a slightly larger opening would clean up the lines and cut away most of the delaminated wood -- epoxy and clamps could close any remaining gaps). I will likely laminate an additional rim inside the cockpit to backup/sister support and prevent similar failure in future (handy to have such great access all around both inside and outside of the cockpit; only the outside has to be finished particularly prettily).

My initial pictures turned out crappy, but here's an example of the cracking and delamination at the back of the cockpit:
http://forums.sailinganarchy.com/uploads/monthly_2018_10/20181017_103503.thumb.jpg.e2a6981f2fb63f05e85ba4b5 2e338de2.jpg
The edges (especially where the straps lay) are worse, but still don't extend into the hull much over an inch.

After I get the unlaminated wood relaminated and the underlying shape of the curve cleaned up, I'd like to cover the double-diagonal endgrain. The hull is skinned with 'glass, and finishing with a wrap over that edge seems wise... or perhaps additionally, where crew might choose to sit, a shelf like the pictured gorgeous black-over-mahogany GBE. A few well-placed slots in such a shelf could better-spread the load from travel strapping (I think the straps have been hard on the exposed edges... moreso than sailor shoes or butts). 
http://forums.sailinganarchy.com/uploads/monthly_2018_10/20180729_134253.thumb.jpg.6c3e45093c2837f382fb7ff2 6c8e0fca.jpg

Randii

randii
10-19-2018, 01:36 PM
I'm looking for a little feedback on:
- flowing thin epoxy (CPES?) into the delaminated areas to stabilize where I need to work (boat was originally built with West System)
- cutting back some of the damage to slightly enlarge the cockpit opening; then evaluate/epoxy/replace any significant remaining delam
- sister-ing in an inner back-up frame (there’s been good feedback on SA about laminating in thin ply to build up strength and retain the existing curves)
- putting new wood atop at least the horizontal surfaces to reinforce and cover/protect the cleaned up edge.
All the above assumes I’m working on dry, dry wood. This boat was stored inside for years, and I trailered cross country through one rainstorm. I’m drying/desiccating for a month under clear cover in sunny Northern California.

The first step above is almost unavoidable -- something's gotta be done. The second step will correct a scalloped, uneven cut. This boat has had multiple owners, I almost wonder if it has already been cut back once in its lifetime, because the uneven line is out-of-synch with the rest of the conscientious construction, and there’s no glass rounded over these cockpit edges (even though the rest of the hull is sheathed with it). The third and fourth steps makes sense to me, as reinforcement, but are kinda optional, and adding weight is always a consideration on a catamaran. Still, the thickness of wood added here would compensate for material removed in the second step.

Your thoughts?

Randii

randii
10-19-2018, 07:53 PM
Interesting. Reading through the study plans, "the cabins and decks are built by a technique called french carvel in which quite large sheets of ply are laid from gunwhale to gunwhale."
That's handy, in that if anything goes horribly wrong, deck replacement doesn't cut into the cold-molded double-diagonals, which are a bit more involved to properly repair (separate, scarf, etc.)

Randii