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randii

Cockpit Coaming Repair

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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 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.

The attached picture shows some of the existing damage. My other pictures didn't turn out very well.

20181017_103503.jpg

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After I get the underlying curve cleaned up and the unlaminated wood relaminated, I'd like to cover the endgrain. The hull is skinned with 'glass, and finishing with a wrap over the coaming 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).

Randii

20180729_134253.jpg

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I'm looking for a little feedback on:
- cutting back some of the damage, cleaning up what's left, and flowing epoxy into the few delaminated areas that remain (this last bit will be the messiest and hardest).
- sister-ing in an inner back-up frame
- putting new wood atop at least the horizontal surfaces to reinforce and cover/protect the cleaned up edge.

The first step is almost unavoidable -- something's gotta be done. The second step makes sense to me, as reinforcement. The third step is kinda optional, but the thicness of wood restored here would compensate for material removed in the first step.

Thoughts?

Randii

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Cutting back, as you suggest, will be easy.  Making a symetrical cut (removing even sound wood if necessary) will make the repair symmetrical as well, which may make it easier to do; if you laminate thin strips into place, they will bend evenly into the space and clamping them while the epoxy sets would be the same all along the face, so the pieces will have less tendency to slide around. 

Though it may help, adding stringers or an inner back-up frame may not be necessary. The existing coaming lasted a decent bit already, no?  You probably plan to cut away the damaged portion and then fill in with thin strips that "overfill" the coaming area, then pare back the "overfill" to the line you want it to have and 'glass over that. The strips would cover the plywood end-grain you mentioned wanting to keep dry. This is similar to building the oak-strip stem on an otherwise cedar- strip kayak.  

Adding a wooden end piece would be a good reinforcement.  Something with some nice grain could be left varnished to really set it off.  

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I will be drawing on the slightly larger cockpit opening in consideration to symmetry, lines of the boat relative and relative waterline. At risk of stating the obvious... it is much easier to cut more later than to add back when too much is cut away.

Good point on laminating narrower strips sequentially for better fit/bending.

The existing rounded edge (maybe I'm rounding up in calling it a coaming?) has indeed lasted a while... I'll google some cedar strip builds to see what you're referencing in context to oak-strip sterns.

but I'd definitely like to reinforce it a bit. That'll help with any straps that may run across it in the future (though I'm looking for better routing) and should also help with sitting.

Thanks for the feedback.

Randii

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Found a couple of videos that might be informative.  The first has what looks like a neat way for clamping laminates in place for making a rib in a carvel-planked sailboat.  The finished-off rib looks quite nice.

https://www.youtube.com/watch?v=F--pdqwImcM

 

This video shows making canoe stems, which is similar to what I did with my kayaks.  You should be able to use this technique to build up & fill in whatever you cut away in the coaming, and then shape it to your liking.  My kayaks don't have inner stems; I did an "end pour" of epoxy into the bow & stern to hold everything together.  

https://www.youtube.com/watch?v=e7wTGmbxHFM

 

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Thanks for the video links -- much appreciated!

After I get the exposed delamination fully dried, my thoughts are to saturate it with something thin/runny like CPES, then cut it back. I think I'll add reinforcing laminates to the inboard skin (handy to have such great access all around both inside and outside of the cockpit; only the outside has to be finished particularly prettily). I’d love to top-cap with a U section, but the cockpit edge follows a fairly multidimension-ed twist at each end that might not allow it). At minimum, I’ll wrap some glass over the exposed endgrain – I was surprised not to see any glass,  ince the hulls are generally skinned with it.

That second video is brilliant for simultaneously laminating multiple layers in a 2D curve. I’m envisioning applying single layers of laminates, but that video and also the first one (forming laminates against an existing skin) will be great if I decide to add a subframe inside the cockpit opening, especially if I run it down to the floor to brace against loads from transport straps.

Randii

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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

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