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Sorry about the typo in the title. Today truly is January 21. We finally found the plank we were looking for on the starboard face of the bottom. By the time we leave the shop tonight, the final six port “bow section” planks will be sealed and screwed down, and the first coat of 3M Premium Marine epoxy filler will have been applied to the fastener countersinks. A second application will follow tomorrow morning, at which time we will allow the 3M 5200 to cure for a week before we sand the countersinks and finish fairing the bottom with Premium Marine filler.
Yes, we use Acetone as our go-to solvent throughout the shop. In this application, and unlike Interlux 202, 333 or 216, the Acetone flashes immediately and in our experience and in the literature actually accelerates the curing process. (We tested the other solvents on 5200, only to find that they actually retarded, and in some cases seriously so, the curing process.)
We will begin applying five coats of Interlux 2000E two-part epoxy barrier coat next week, followed by three coats of Pettit Copper Bronze antifouling bottom paint.
Soon Minnow will be equipped with what in Danenberg’s world constitutes a true 5200 bottom.
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Installing the Minnow’s True 5200 Bottom is progressing nicely. Three-quarters of the bottom planks have been fabricated, which has turned into a near-Herculean task. Why? None of the planks has parallel sides, and the degree to which each plank tapers from chine to keel differs from board to board.
And using the boards from one side as patterns for the other? Well, they are close, but close does not deliver perfect mating with the two boards on either side of the one being fabricated.
John has patiently sanded every plank in using our 36” horizontal, stationary belt sander.
As you see, we lay all the planks out, placing one positioning fastener in each, and then laying out a grid for all the fasteners, and drilling all of the countersink holes, so that the planks end up screwed down where we want them to be.
We test as we go, choosing between #6 and #8 silicon bronze, Frierson wood screws ranging from ¾” to 1-1/2” long.
Why not stainless? Read Danenberg’s article in the Sept-Oct 2014 issue of Classic Boating magazine to find the clearest, science-based, and most objective explanation I have read yet.
Each plank is literally buttered with a 1/8” thick layer of white 3M 5200. Why not mahogany? It costs about 50% more because of the color alone. Since it will end up hidden by five coats of Interlux 2000E Epoxy Barrier Coat Primer, selecting mahogany just wastes money.
As you see, John drives the screws in with an impact gun, and then pounds and pounds the edge of the plank with a large rubber hammer. Doing so drives the 5200 all the way out and beyond the plank’s edge.
What we did not show was the next, not-so-fun step, cleaning the excess 5200 from the plank’s face, edge and surrounding area. Pay special attention to cleaning the trailing edge so that the next plank fits snuggly in place.
Interlux will happily sell you 202 or 216, or some other more exotic solvent. Acetone is our go-to solvent throughout the shop. Unlike the expensive thinners, it flashes off almost immediately, and leaves no residue behind, oily or otherwise.
As John remarks in the clip, “There is nothing clean about installing planks as part of a true 5200 bottom!
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We have been so busy making progress elsewhere that we have been unable to get back to the 1930 Dodge Runabout 5200 bottom project until yesterday.
As of this mid-afternoon yesterday, John, RJ and I have finished re-sawing and milling FAS grade mahogany planks – 6/4×18”x16.5’ – into a collection of 1/4×6-1/2”x48” bottom planking blanks.
John then began fabricating new bottom planks, one-by-one, since ever one is different from all the others. We find John now having fabricated all of the starboard planks, and, as the clip closes, beginning to seal each of them on all four sides with CPES.
We hope to begin screwing them down, heavily bedded in 3M 5200. In his recent article, “What is a True 5200 Bottom?” (Classic Boating, September/October, 2014), Don Danenberg is blunt about how skimping on 5200 simply translates into fool’s errand now, and troubles lurking on the horizon:
In communication with the two 3M scientists who invented and developed the 5200 product, I was told that one of their first, largest customers was Chris-Craft, who used it to replace the two-part Thiokol they were currently using in the plywood Cavalier and Sea-Skiff divisions. It was apparently tried in the main division of planked boats but added far too much in construction costs to be cost-effective. Higher-end boat builders, like Trumpy
Yacht Company, used it as their standard construction procedure after 1966.
The biggest problem I’ve seen here is inadequate amounts being used. Where I recommend 40 to 60 tubes just for the bottom plank installation, these troubled guys reported they had been billed for 24 tubes. This is simply not enough product to fill all voids. Okay, so you saved a few hundred bucks, but compromised the entire operation?” (p. 24.)
Also following Danenberg, five coats of Interlux 2000E Barrier Coat Primer will be applied once the bottom has been installed and the 5200 has cured, a process that takes 7 days.
Quoting Danenberg again from the same article:
“One of the biggest problems I have seen with short-cut 5200 bottoms is either a total lack of, or inadequate amounts of, Interlux 2000E Barrier Coat Primer. This two-part (thus epoxy) paint is a water barrier coats meant to keep the water from soaking into the bottom planks. It does that with minute platelets in the makeup that vastly slow the movement of water. Unlike hard epoxy laminating glues, it is flexible enough to move with the bottom.” (p. 25.)
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