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August 1, 2001 Issue


August 15, 2001 Issue




August 1, 2001

Bolger on Design

Design #304 - Fiberglass Workboat

This boat was designed for yard use in the U.S. Virgin Islands, with good rough water ability to go outside shelter in bad condi-tions. She was designed to go faster than displacement speed (which would be less than seven knots on this length) but not much faster. Her shape would be capable of 10 knots, even 12 with enough power, but with quickly diminishing returns of speed for added power. The Lunenburg-built Atlantic engine developed its power at about 400 rpm and could turn a 26" diameter prop. It was make-and-break ignition, direct reversing. In the end it was decided to install a more mod-ern engine, a Ford diesel, somewhat of a pity as direct reversing engines are fascinating to listen to in maneuvering as their resonant "choom" slows down and stops with what seems like an interminable pause before they start up again in reverse. They can still be heard, for instance, in European river barges, but those are diesels and they have compressed air starting. The Atlantic was hand starting, and while the massive flywheel makes the action reliable, it did seem that dealing with it might be an unhealthy distraction in some intricate maneuver.

The hull was built by the C-Flex method, very rugged but hard to get really fair and smooth. It was intended to use the first one as a mold plug to build more of them but, as the photos show, her finish and fairing are not good enough for that and the apparent market did not justify a dedicated plug. We understand that the single one built came well up to expectations, dry in a head sea, steady in a following sea, and good to maneuver. The only criticism of her was that she didn't hold on against a beam wind as well as would have been desirable. This may have been corrected by adding sonic keel area amidships and forward. There was a generous amount of foam buoyancy in the bilge spaces and all around the sides to float her level and upright with all possible flooding.

The fiberglass construction encouraged making her very curvy, although except for the compound curved round stern and the soft nose stein, there's nothing that would irritate a boat builder used to conventional wood con-structions, and skilled old-time yacht builders would have dealt with those. It's noticeable in the photos that the C-Flex one-off method ended up with a ridge instead of the intended ellipse at the stem head. The round stem is really an extreme case of a curved transom as all the buttock lines run straight back as they would with a conventional motorboat transom. Rounding it off removes the vulnerable comer of the transom when maneuver-ing in tight places.



August 15, 2001

How To Keep Epoxy From Getting All Over You and Everything Else

By Robb White

Despite the initial impression of casual observers, I am a very neat person ... in my own way. I do not like nastiness, and I especially don't like to get epoxy on me or my tools or smeared all over my shop. But I believe that by using epoxy to glue good wood together and seal it, it is possible to build the best small boats ever in this world. You have to know what you are doing, though, or you are liable to wind up with such a mess that the cure is sort of like what the old farmer told me when I asked what was the best thing to do to get nut grass out of my garden. "Move," he said.

I am not about to accept any liability for any mess you may make when you strike out on your own after reading this. As soon as I get it in the mail, I am going to move ... to Monrovia, Liberia, or Colon, Panama, just like an oil company so I will be beyond the reach of the law. Like I said, you have to know what you are doing to get this to work right. But if you do, it is possible to put a whole boat together, completely coat and even sheathe it with fiberglass and epoxy without ever putting on a rubber glove and without a single drip of epoxy on the floor or a smear on your clothes or tools.

Here is how it works. You use the natural ability of the wood to attract epoxy by molecular attraction ... you put the epoxy on the outside of the joinery and let it soak in. First you put the boat together dry with some kind of other fastening. I use all sorts of steel square-drive mobile home screws, cyanoacrylate glue, clamps, tape, string, wire, staples ... anything. It is sort of fun building a boat like that, The only tricky part is that all the parts must fit close enough that all the cracks are tight enough to act as a capillary so that the natural physical attraction between the molecules of the epoxy and those of the wood is stronger than the force exerted by gravity on the mass of the epoxy. What that means is that the scams have to be little enough so the damned stuff won't run out. That's a good thing ... things just have to fit ... ain't nothing wrong with that.

Here is what I did to decide to do it this way a long time ago, and I suggest that you do these same experiments using your wood and epoxy in your shop so you can see what you can get away with. I made up a bunch of testjoints ... things like joints with end grain to face grain, end-to-end, face-to-face, multiple laminations, joints with a fiberglass screed between the two wood surfaces, joints where both surfaces were planed or sanded or where one surface was planed and the other sanded.

I did it under different conditions of temperature and humidity and even falling and rising barometric pressure. I did it when the wood was hot or cold or the epoxy hot or cold and every which-a-way between those. I like to do that kind of thing. I would heap rather do that than watch the TV.

What I found out is (and I am going to condense this ... ain't no point trying to lead somebody by the hand into sucfi risky business) that hot, cooling wood with freshly sanded 40 grit surfaces is most attractive to epoxy molecules. I found that under my circumstances, I can count on 5/8" penetration into a capillary sizedJoint from one side and 1- 1/8" if I can apply the epoxy to both sides. That means that I can do something like laminate up a stem using a few drops of cyanoacrylate to hold the plies together, and just heat the assembly and paint the edges and continue to paint the edges while the hot wood cools and the contraction of the gasses in the cracks (and indeed within the interstices of the wood) draws that epoxy in. The wood has to be hot all the way through and wood is an excellent insulator so it takes a long time with the heat lamp to do such a thing.

I'll leave the ingenuity up to you, but the way I do it is to heat my tiny shop with the old wood heater that came out of the railroad station in town back when there was such a thing. It don't take long before the spiders are all out hunting them a new home. I keep it hot like that (130oF works for me) for several hours and then cool the air in there with a big AC and then put the first coat (takes three for me) on the whole boat at one time. Then I stand around and watch all the cracks to make sure I keep them fed as the cooling draws in the epoxy.

You have to really pay attention to any joint involving end-grain. I use a heat gun to thin the epoxy and expedite the soaking. The heat thinned epoxy acts almost like it has an evaporating solvent in it and doesn't want to run quite as bad initially and hardens up pretty quick too. It works well. I never apply epoxy to anything that I haven't heated, and I never fail to sweep it with the heat gun after it is on there either. Sheathing hot wood with fiberglass and a heat gun is a revelation.

The best thing to spread epoxy on large, smooth surfaces is a plastic squeegee. If the surface is not suitable for that, then the next best thing is a special epoxy roller. Tipping behind the roller with a brush will help smooth the job and tipping behind the roller with a brush and heat gun will do even better. That squeegee and roller will do it the easiest but I don't have many places on my boats, particularly inside, where I can do it that easy way. I have to use a little brush and, boy, until I learned how, that was an infuriating business.

First, I like a 1-1/2" brush. I used to think that the best thing to do was just to splurge and go ahead and use a pretty good brush, but I found that a pretty good brush holds too much epoxy and not only results in a runny job but gets hot up by the shank sooner. A regular "chip" brush is best but they'll shed bristles and are too limp to spread out epoxy in a thin enough coat, even with the reduced viscosity induced by the heat gun, overcome the molecular attraction, Here is how to fix a chip brush so that gravity can't to keep it from running.

First, cut the bristles off about halfway up with the shaving sharp knife from right out of your pocket. I I ike to cut from both sides so I wind up with a blunt taper to the ends. When you get it trimmed to suit you, trim five or six more. Half-cured epoxy in a brush makes a messy mess. Then sand the bristles on a high-speed sander. I used to use a disc sander with 40 grit paper, but now I have a big, stationary edge-sander standing by ... also with 40 grit so I use it. Sand the ends of the bristles from all directions, even backwards like you ain't supposed to rub a cat. You'll see the loose ones flying the whole time and the ones that stay with you will get fuzzy and uniformly shaped by the sanding.

After you no longer notice any loose bristles being removed (some chip brushes never stop until all you have is the handle and the ferrule), proceed to the next step, which is to wire brush the bristles with a bench grinder. That'll separate the wheat from the chaff and the men from the boys and ... dirty the brush if the wire brush was rusty or contaminated in some other way. A brush that makes it through that treatment will (which reminds me of a friend who checked out used cars by driving them from Moultrie to Funston, 20 miles, wide open ... in first gear) when accompanied by a heat gun, do a good job of applying epoxy.

Most of my boats are built lapstrake with the planks already warped to fit and pre-sheathed with epoxy and fiberglass on the bench under heat lamps before being screwed to the boat. I have to put one more coat of ep-oxy on the sheathing to fill the weave of the cloth, but I like to do it very carefully so as not to have to scrape off any runs. If I have to feed the capillary-sized laps at the same time that I apply the final coat, the result is not as neat as if I first feed the laps with a plastic syringe. It is sort of like welding. I just walk along the heated boat and apply a little bead of naked epoxy to the inside comer of each lap and sweep it with the heat gun. It is easy to see a tiny emiscus of epoxy appear on the other side almost immediately as I walk along.

The two fiberglassed surfaces within the lap are very attractive to the new epoxy, and the epoxified and sheathed wood does not soak epoxy out of the joint so it is a one-pass business ... most satisfying when I remember the bitch of a time I used to have building a glued-lap boat back in the old days when I had to put the glue on the laps and then fight the board into place ... with my rubber gloves trying to stick to the drill. To hell with that kind of thing.

I'll repeat the caveats:




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