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CJ
08-25-2014, 11:49 PM
This is my first strip built boat, the Ocean Pointer, and I'm a bit frightened by something that I noticed the other day. First a little background:



Cedar bead & cove strips 3/4" x 1-1/4" with 3/4" meranti ply frames.
Strips are edge nailed to the previous strip with SiBr ring nails every 10" - 12"
Strips are also glued to the previous strip with PL Premium
Strips are also each nailed to each station frame (plywood) which are spaced about 18" apart also using SiBr ring nails which were set well below the surface of the strips >1/8"
Each nail head was then filled with West System epoxy / fairing compound and the entire hull sanded smooth
Then the whole hull was fiberglassed with 10 oz cloth set in epoxy, followed by multiple successive coats of epoxy to fill the weave
Painstakingly faired the hull
Two coats of Interlux epoxykote primer
So far only one coat of Interlux Brightsides black has been applied


Very happy at this point; hull looks great. Now, due to a relocation including a house gut job, the boat has sat for about 1 1/2 years witout any further work. It's been covered, outside, with a heavy, plastic, flame-resistant tarp tied tightly to the trailer in a tent-like fashion so air could move through fore & aft.

Finally have time to start working on it again, lift up the tarp and find that the ring nails which were nailed perpendicularly through the strips into the frames and subsequently filled & faired, have somehow caused a small bump to appear at every nail location (nails in question circled in red below). The bumps are small, but certainly noticeable, but I couldn't capture them in a picture. They almost look like tiny rivet heads pushing outward on the 'glass.

What is causing this, and will it continue? I can't imagine the ring nails are somehow moving outward. The epoxy I used to fill the set nail heads wouldn't swell up or anything, so ????

Also, what do I do now? I can probably sand all these bumps smooth again without cutting into the fiberglass since they're not that pronounced (yet), but I want to make sure that there isn't something else going on here that I should be aware of before I try to fix the problem.

Picture showing the location of all the nails that now have raised bumps over them and one picture just after applying the first coat of black when all was good.

http://i255.photobucket.com/albums/hh147/cjg0601/OP_zps0d10c335.jpg


http://i255.photobucket.com/albums/hh147/cjg0601/OP2_zpsde53dbd5.jpg

MN Dave
08-26-2014, 01:00 AM
Nice looking boat.

Your problem may be the combination of black paint, sunlight, tarps, time and heat. West System 410 Microlight filler by any chance? The acrylic microspheres in 410 tend to expand with heat. The filler can swell when it gets hot. The thickest filler is right over the heads of the nails, so the lumps are probably swollen filler, not rising nails. Will it stop? It has to slow down eventually, and 1 1/2 years is a long time. Shiny dark colors visually accentuate tiny defects. I have a friend who worked for Chrysler and Toyota on the paint lines. The first cars off the line were white because white hides the defects.


Another vote for "live with it and pick a different color for the next paintjob".
Launch the boat. half the problem is under water, and you can't see any of it from where you sit. :>)

Gib Etheridge
08-26-2014, 01:19 AM
My guess is that the vertical grain strips shrunk in thickness. Odd though that it didn't affect the entire hull, but that could be because only that particular area of the hull got hot enough.

If that's the cause you can just set the nails a bit deeper and refill the holes.

Another possibility is that the unfinished/not sealed inside of the hull absorbed atmospheric moisture and swelled and pulled the nails out a bit then shrunk again and the nails popped. Quite possible since nails don't hold very well in plywood edges.

That's a very nice looking hull CJ.

CJ
08-26-2014, 02:26 AM
Dave's theory might be a valid one. Yes, I did use 410 over the nail heads, and although both sides of the boat have the same issue, the side of the boat which is exposed to the sun is worse. There are other areas of the hull where I used 410 to fair some spots, but they aren't a problem; just those with nails under them.

Gib - not sure how I'd reset the nails without digging out each one (through the fiberglass, dig out the fairing compound and work my way back out, but then I'd have penetrations all over the 'glass sheathing, ugh. I always thought that ring nails into the edge of plywood was the preferred way to go. In addition to the perpendicular nails being driven into the frames, there's also an epoxy fillet on the inside, along both sides of each frame which also holds the strips to the frames. You think they could still move? Thanks for the compliment; I love the look of this hull.

CJ

Peerie Maa
08-26-2014, 06:08 AM
My guess is that the vertical grain strips shrunk in thickness. Odd though that it didn't affect the entire hull, but that could be because only that particular area of the hull got hot enough.If that's the cause you can just set the nails a bit deeper and refill the holes.Another possibility is that the unfinished/not sealed inside of the hull absorbed atmospheric moisture and swelled and pulled the nails out a bit then shrunk again and the nails popped. Quite possible since nails don't hold very well in plywood edges.That's a very nice looking hull CJ.It is most likely caused by changing humifity causing the filler to move towards the surface as the wood comes and goes. I expect the movement ws too small to pop the nails. As you have glued the strips to the frames that is both unlikely and irrelevant.I think that all you can do is let the hulls humidity stabilise after finish coating the inside, then fair down the blebs and finish painting. Once the wood is stable the problem should not recur.

wizbang 13
08-26-2014, 06:52 AM
All of the above.
Black,not just black but SHINY black!!
Nails set too lightly and set into end grain of ply .
410 used as putty .It is only recommended for under an eighth of an inch fairing.
I would have (easy to say)used laminated timber frames,and still only nailed the the hull to every third or fourth plank.
That said, epoxy putty over fastenings WILL tend to telegraph through . Through paint, resin, even fairly heavy cloth.
For a perfect job , wood bungs ARE the cats jammies. This is why I never seek perfection.
I think you only have a problem if you NEED to make it perfect. As you say , resanding will only make the sheathing thinner ,then you have a catch 22.
The boat is over the top good looking , you may be the only person who notices after the other bits go on .
I recommend at the very least to give her time .
bruce

sdowney717
08-26-2014, 09:11 AM
Resanding will only make the sheathing thinner, yes.

I would not go digging out the nail heads. How about punching the nails back down without any sanding, right on top of the glass, then fair sand and paint. Experiment with a few to see how it goes.

Or drill a little hole on top of each nail head and set the nails deep then fair and paint.

Or just live with it, it can always be fixed later. This boat is going to eventually someday need a new paint job

The wood has moved, expanded and shrunk cycling over time and the nails are telegraphing through because the wood has moved and maybe the filler was too weak to prevent that wood from working and showing.

Figment
08-26-2014, 02:20 PM
Another vote for "live with it and pick a different color for the next paintjob".