Coaming boards - Is epoxy flexible enough to conform to the bend?

[chrisncate]

A coaming needs to bend in towards the cockpit part that it bolts to, inward (about a five inch deflection on a 10' piece).

Would epoxy crack?

[CalebD]

One word: NO.
Another non-word: Cetol (Natural Teak of course)

My experience was that for the work I put into epoxying various bits of exterior teak and then trying to varnish over them for UV protection was not at all encouraging. Unless you are willing to stand up to the hard mistress the Varnish is then you will never keep up with the recommended # of coats and the epoxy undercoating WILL start to fail after 2 - 3 years. It will pull up from the surface of your expensive teak or whatever wood is on your boat and you will need to take it all off again in order to finish it properly.
Some urethane varnishes (2 part varnishes that smell like nail polish) promise more long lasting results but I am in no way convinced that the time and effort is worth the expense.
I've tried Interlux Shooner varnish, Bristol Finish (BF) and Cetol and guess which is my running favorite right now? I'll give you a hint: it's not BF or varnish.
The reasons are simple. Cetol is easy to use by even a lobster, it only requires maintenance about once a year and it does not smell like a nail polish factory.
Your mileage will vary.

[dacap06]

Regular epoxy doesn't flex enough for your purpose. The rather expensive G/Flex 650 might, but I'm with Caleb on this one. I think your best bet is Cetol.

[JimsCAL]

Sounds like the epoxy may be part of the attachment, not the coating. If so, G/Flex may be the way to go. I've used the thickened stuff that comes in a pair of tubes and it works well. Does cure pretty slowly however.

[PorFin]

Originally Posted by chrisncate

The coaming needs to bend in towards the cockpit part that it bolts to, inward (about a five inch deflection on a 10' piece).

I need to install it with cured epoxy where it bolts up, and bed it. Will the epoxy crack you think? I plan on varnish over the rest of the epoxied coaming upon install.

West system epoxy.

Thanks in advance for any insight offered.

CnC,

I'm not quite sure what you have in mind, so I'm not going to discount the suitability of epoxy out of hand.

Could you explain your tentative plan in a little more detail? Are you laminating a new coaming using epoxy?

[Faster]

Chris... are you planning on fabricating new 'boards' in place of the original teak? Not real clear from your description. Sounds like everyone else assumes you're treating original teak boards.

[emoney]

Is the epoxy only going where the two pieces meet, in the "bolt up area"? If so, how much of a bend is there?

[hellosailor]

If you want to put a 5" curve in a ten foot board, you don't want to do it that simply.

Traditionally you would steam the board, and you could use a 10-12' long piece of venitlation duct as an improvised steam chamber for this board. Once it is nice and soggy, you take it out, set it in a jig, and let it dry. it will take on the curved shape and hold it.

Or, you don't use a solid board. You use 1/4" or thinner plies, set them in a jig and glue them up and clamp them. When the glue dries (epoxy or a water-proof alternate) again you'll have a curved board.

But to just force a board into that kind of curve? That's brute force, and the board will forever after be fighting whatever you do, trying to get straight again.

[PorFin]

Originally Posted by chrisncate

I described it poorly, a pic will probably do better explaining than I:

Old pic of old coamings, the new ones are already made, dry fitted up and ready to go on. They are Sapelee mahogany, not teak. See the slight bend? Notice how it also connects to the boat - that's the area I need to figure out how to get a finish on before the install, so it's sealed and protected where it bolts up. Where it connects is about a 3" area along the lower part of the board where it seats into the impression molded into the boat..

CnC,

I'm still a little unsure of what you have in mind, but does this sound right?

You've cut replacement coamings out of Sapele. These are made out of flat stock. You are trying to figure out how to secure them to the boat while accomodating the bend in the cockpit.

I think you're facing a choice of either doing a) what works; and b) what's best.

At this stage in your project, I'm going to side with HS and recommend steam bending the pieces before installation. While you can likely muscle them into place using the through bolts and epoxy, the coamings will always be trying to return to their original flat shape. The combination of these pressures and UV degradation pose a risk of failure. If you steam bend the pieces, you won't need the adhesive proerties of epoxy -- a combo of mechanical fasteners and a decent bedding compound will be sufficient. This will also make it practical to remove them for refinishing in the future; if you epoxy them, that's probably going to entail partial destruction.

[CalebD]

So let's see if I finally understand the question here.
There is a 3" deep channel that your coaming boards will fit into? before being bolted through the deck and this is the part of the board you are wondering how to finish?
If the exposed parts of the coaming boards are going to be done in varnish then why not use a few coats of varnish for the 'buried' ends? A coat or two of epoxy would also likely work but ... any finish on this part of the board could simply act to hold moisture in the board. I would think that the important aspect of this joint would be to bed the coamings really well with something like Butyl tape to help keep moisture out of there in the first place. Seems to me that Butyl would be an ideal bedding compound for this application.
As far as the slight bend in the coamings I'll only ask how thick is the Mahogany stock you are using? When replacing sections of our teak toe rail we just screw it and bend it but that is more like 1/2" stock. Maybe a little steam bending as HS suggests if it is 3/4" or thicker stock?
Any pics of the channel the new coaming boards fit into?