|Setting up the Jig|
Let’s start by noting that the bottom of a TriloBoat hull (box barge/scow) is not rocket science. It has a couple of curves, yes, but these are easily dealt with. So lets roll up our sleeves and walk through it.
There are two ways to go about building any boat… right-side up or upside down. For TriloBoats, I’m tending these days to right-side up. A couple of steps are harder, this way, but we don’t have to build any temporary structures, and we don’t have to turn the boat… a task that still freaks me out despite many successful roll-overs (no failures, so far). For this post, I’ll stick with right-side up.
For Andy Stoner’s MARY ELIZABETH (T32x12), we spent a week indoors building components. Deadflat sections (the flat portion of the bottom between end curves), side sections, bulkheads and transoms.
At the end of that week, we set up the building jig. This consists of two substantial beams that run about one half the overall boat length. You should set up as low as possible, while still being able to swing a hammer underneath the boat-to-be.
Prop ’em up on solid blocking, and parallel. To check for parallelity, measure between them and adjust until equidistant (parallel in plan view). Then eyeball across opposite edges and adjust one end of one beam until edges align (parallel in profile). Finally , lay a straight edge across their upper faces and adjust until it lies flat across both at all points (coordinate their rotation). Repeat until all satisfy, then block and shim securely into position.
Note that this accounts for square and true, but not plumb. TriloBoats are self-rectifying, so plumb is elective. If you’re type-A, go ahead and adjust for plumb with a level.
|A few terms for our discussion|
|8ft sheets on 12ft beam…
Lots of extra work.
Note jig is not level.
Once the jig is ready, lay out the deadflat components in order. Depending on how you’re going about things, these could range from plain, full sheets of ply to pre-fabbed and finished stacks of ply (layers offset to provide overlap at the butts… minimum 1ft). Glue ’em up and join them, one component at a time.
I prefer at least one of these layers to be 3/4″ ply. This is thick enough to accept ringshank nails, which provide a good lock and clamping pressure until glue dries. Butts may be backed up, later, by fiberglass tape set in resin, straddling the butt seams. Waterproof, and adds a LOT of strength.
Once the deadflat is together, you’ve got a big, flat platform. Join and frame the side panels… let set up overnight. Next day, pull aside, erect bulkheads on your marks, position sides and join to bulkheads and bottom. This day is exciting. Lots of friends help… reward with pizza, beverages and music.
Blah, blah, blah… boatbuilding deets… you may build the rest of the boat before you get to the bottom end curves.
The important thing to know, at this point, is that the side panels are framed along their bottom edge with 2x lumber. Installed, they form the jig for shaping the bottom. Their framing’s lower edge faces provide area for gluing and beef for nailing. All thwartships, bottom planks (sheets of ply) overlap side panel framing and planking, ending up flush with the outboard faces. All sheets full size!
Both ends of the deadflat have offset courses of ply, resulting in a flap at each end. Make sure this is clean and clear of glue (may have to cut some goosh out). End curve courses join this flap, and continue the offsets in the steps below.
Thick or stiff ply doesn’t like to bend. It want’s to stay flat or pretty close. So we coax it along.
One thing that helps, while laying out the curves on the side panels (you will have done this a while back) is to let the outboard ends of the curves – 12 to 18 inches – run free (let your batten spring to its natural lack of curve). Your ply courses will be much easier to bring into line, this way, than if you had made the curve continuous (I may have picked this trick up from Lofting by Alan Vaitses?).
|SLACKTIDE’s kerfed 1st course|
The next thing we’ll do is kerf our ply where it’s curved (make thwartships, partial-depth cuts). This lets it bend similar to a roll-top desk. Experiment, and leave as many plies intact as you can while still being able to bend the sheet. If your wood is stiffer, you will need deeper kerfs and space them more closely. For 3/4 AC Fir, we find that leaving 2-3 plies out of 7, and spacing every 3-4 inches works well. Half inch AC Fir may not need kerfing at all.
Lastly, plan ahead to let the bottom run out past the ends. Once done, you’ll trim flush with the transoms, at your leisure.
The first course will be kerfed, if necessary, on it’s outboard face. Don’t need to kerf where the curve runs flat toward its end. When joining, fill kerfs with glue. Plan ahead so that nails are embedded in solid wood (avoid kerfs).
Installing this first course is easy. A cake-walk (that reminds me… don’t start hungry!).
We like polyurethane glue-from-a-caulking-tube for these external hull joins (e.g., 3M5200). It’s moisture activated, slow curing (won’t kick today), gap filling, water-proof, elastomeric, and wicked strong.
Spread glue along flap and framing, a bit further than one sheet will cover. Be generous (want no voids), but don’t over do it (expensive). Look for a bit of glue oozing from between sheet and framing, inside and out, to ensure good contact.
Position sheet, and fasten with nails (we like ring-shanks), working from inboard to outboard. Remember it’s the glue doing the work, the nails are there to clamp and provide moral support. See if one, every other ‘plank’ (space between kerfs), is sufficient; oneevery plank, if not.
Repeat until first course is laid.
|1st layer on ME was 1/2″ (kerfs in 3/4″, 2nd layer, only)
The piecing, shown here, is unnecessary with 12ft sheets (or 8ft beam)…
This has been cobbled from 8fters
The second course is trickier due to time sensitive glue, large area gluing and the need to close gaps between sheets. It’s going to be a much easier job for two than one. Make sure your help knows every step of what’s going to happen before you start. Talk it over and try to spot problem areas in advance.
If the second layer requires kerfing, do so on it’s inboard face (when joined, the kerfs should be hidden between courses). Stagger the kerfs so that they do not match up. Mark guides for nail pattern on the outboard face, avoiding kerfs and first course nail pattern, so you don’t have to guess under pressure.
We like LPU (Liquid PolyUrethane, e.g. Gorilla Glue) for laminating plywood sheets. It’s moisture activated, temperature tolerant, relatively easy clean-up, foams to be gap-filling, and doesn’t take much. Looks and acts like honey. Sets up in about 45 minutes in cold weather, faster when warm. Time a test batch to get the feel. Set up materials near to hand before starting. We get about one sheet per 20oz bottle. Have back-ups… if you run short, you’re in trouble.
Ready? Breath. Note the time and start.
Squeeze glue from the bottle into all kerfs (both layers… use large syringe for overhead kerfs). Squirt a pattern on the second course’s face and spread with long, flat spreaders (paint stir sticks work great). Do this before installing, while it’s lying flat. Move efficiently and without panic. LPU can be spread thin, but you should leave a skim of glue (no areas scraped down to the wood). More won’t hurt, and it’s false economy to use too little.
Position the sheet and start nailing into place, working from inboard toward the ends, forcing gap slack ahead of where you’re fastening. Have persuaders ready to go (props, jacks, screws* with drivers) and use ’em at the first sign of trouble (gaposis). Get it in position and locked down with the effective minimum of fasteners.
Repeat until this section is planked. On this course, try to hit each butt seam between sheets with glue. Once all sheets are in place, go back and fill in your fastener pattern. If in doubt, add more 2x clamps*.
Sit back. Breath. Laugh, dance and hug. Admire your work. Kiss and make up for any harsh and hasty words loosed in the heat of battle. Wipe up excess glue. Assess, address and debrief for the next round.
Job well done!
|Closing up the bow… note blocking, bottle jack and 2×4 clamp,
old clothes, gloves and knee-pads…
and yes, she’s got glue in her hair!
*Screws are very useful for closing up gaps. If there’s no framing to screw into, set up a short section of 2×4 and screw into it, drawing courses together (see photo above). Remove and plug holes after glue sets up. We like high thread count, square-drive screws and a brace or cordless drill. Size screw length for bottom thickness plus 1 1/2+ inches.
Originally posted 2012-02-09 07:15:04.