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Anke and I live aboard WAYWARD, and wrote about it's design and construction at

Access to the net comes and goes, so I'll be writing in fits and spurts.Please feel free to browse the archives, leave comments where you will and write... I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirly gmail daughter com

Saturday, March 1, 2014

Piecing the Bottom Together: A New Approach

First layer of aft End Curve built on its Nailers

NOTE: This post is an alternative to methods presented in  Barge/Scow Bottom Planking: Making it So, which introduces terminology. Since this writing, we've completed the bottom of our new boat using the methods presented here. Went off without a hitch!

Any order is a balancing act of extreme precariousness.
- From Illuminations: Essays and Reflections by Walter Benjamin

Piecing the Bottom Together: A New Approach

The one thing in boatbuilding that scares me is turning a hull.

Building upside-down has a lot of advantages. Gravity works with you, rather than against you. Especially when it comes to sheathing - which can be floppy or limp - it helps to have Mother Earth pulling for you. When it comes to painting, it helps to be on the upside of the gravity well.

We've turned two of our boats, now; ZOON and SLACKTIDE.

ZOON is a twenty footer, barely more than a skiff, so wasn't bad, weighing about 500lbs at the point we turned her. A bunch of friends and a stack of tires (to catch her fall) did the trick.

SLACKTIDE was another matter. She was well past a ton, and copper plated. Anke and I did it alone, using a hydraulic jack, a lot of blocking and tires again. Went smoothly, but it left me cotton-mouthed and wobbly in the knees. It's something to see your baby towering above your head, balanced precariously on one chine, kitty-corner and cock-eyed. 

And then to drop her on to tires... well... it's quicker than lowering, but dramatic.

For LUNA (our Bolgeresque Advanced Sharpie at 31x8 feet), we built the bottom upside-down, turned that, then built upwards from there. Alas, this sensible, sharpie approach wasn't matched by cash flow. We bought copper plate at a later date and installed it on a grid between tides. Don't recommend it.

So now we're planning our latest, a T32x8 LUNA (blogging the process at, and have been waffling over which way should be up.

And then... a brainstorm!

The basic idea is to build the bottom planking as components - two layers of plywood, a 'gasket' of some sort, and copper plate - and then assemble them into the finished bottom.

Build and finish components upside down, then flip upright.

Join components into continuous 'skin'

So far, this approach isn't new to us. We used a similar method to piece together the deadflat of Andy Stoner's MARY ELISABETH (top photo). But a barge's high rising bottom curves at the ends discourage a partial build of the inverted lower hull. It seemed all-or-nothing: a big, scary boat to turn, or suffer through overhead work at the ends (our final choice).

So what to do about the end curves? 

A huge, box barge/scow advantage is that the boat itself is it's own jig. No molds or frames apart from its own structure. But aha! A strategic exception can help, here!

Use the nailers - sawn chine timbers that join the end curves to the sides - to build a jig before installing them (separate from the hull proper)!  This lets us build curved components at ground level, just like we did with the flat ones. 

Simply laminate the ply layers in position on the jig, remove once glue sets, and finish with gasket and copper (or any sheathing of choice). Set aside and proceed as normal for an upright build, installing once the hull structure is established, using the same joining methods as if they were flat.

Typical End Curve Jig
End bracing optional... the curved ply overlay provides 3D rigidity
once (correctly) placed and fastened

Note that the fore and aft curves are typically different, so two jigs will be necessary where the ends are not symmetrical. The middle piece (made from scrap) may not be necessary, in narrow hulls, or you may want more in wider ones.

So there ya have it. 

There's a lot more finnicky detail that goes into executing this plan. Resin/Fabric bottoms will require a modified approach, and may need touch up at seams and fasteners. Plate fasteners need special treatment. Bottom to bulkhead, side and stringer fasteners need to be longer (more expensive) than if building a sheet at a time.

But I'd rather be scratching my head than tossing over turning!

NOTE: Andy Stoner's MARY ELIZABETH was built upright, with the ends built in place, overhead as documented in Barge/Scow Bottom Planking: Making it So. She relied on skegs for grounding protection, and was neither sheathed, nor copper plated.


  1. [Response to an eMail from JOHN]

    Hi John,

    Good questions all! I called them the 'finnicky details' in the post. My answers, here, are just one way among many that others have figured out.

    John: I was thinking about how you might pre-shape the curved pieces for the ends of the hull using the final curved side pieces as a template. I'm thinking that even though the inner and outer pieces of plywood will be glued together, they most likely will spring to a flatter arc when released from the "mold". If that happens, will that be a problem for whatever method you use to attach the copper?

    Dave: I'm guessing that there will be a little play... meaning that the copper (screwed, in our case) will allow a little flex-to-fit.

    Still, we'll 'overbend' the ply, slightly to stay as close to true shape as possible. As I recall, we added about an eight of an inch every 4ft, using shims above the true curve at mid-span. I'm going to research this further, but as I recall, it's what we've used before for laminating arcs.

    (See below... this answer has been superseded).

    John: I'm also thinking that the two layers of plywood, at least 8'x8', plus the copper, could result in a pretty heavy piece. How will you move and position that heavy of a component.

    Dave: Yep. Depending on our set-up options, we may just do 4ft x 4ft sections, plus overlaps, to keep weight low. But even if it's 8ft x 8ft, flipping them is easy compared to a hull!

    Two layers of 3/4in ply weigh about 150lbs, and a 4ft x 8ft x 1/8in plate of copper weigh about 185lbs, for a total of about 235lbs. The end curves, joined, would come to about 375lbs... not too bad.

    We'll build the deadflat components on the two-beam jig, flipping each (around one edge, so half the weight to lift), and joining.

    Now we've got a big, flat workspace. Build the nailer jigs, then each panel. Flip, and scoot to their ends where the wait until the sides are up. Position with glue and lift the outboard end while fastening from inboard.

    The tricky ones, if we do 4ft components, will be the very ends, since their inboard ends are above the deadflat (supported) level. Thus we'd need a tricky scaffolding-like arrangement. Argues for 8ft x 8ft and taking our medicine in a heavy but straightforward flip job.

    [Continued, next comment...]

    1. [...Continued]

      John: Finally, how will you assemble, then remove the plywood from the curved templates? If you screw (my assumption) the inner layer to the template pieces, then glue outer plywood to the inner plywood, how will then unscrew the inner plywood? I'm sure you've got some clever idea worked out, but those curved ends will definitely be trickier than the deadflat portion.

      Dave: Well, not too tricky... a very few, smooth nails (easily pulled) to tack down the kerfed piece, then longer, temporary screws through both layers and into the nailers. We'll be using some heavy lag screws, later in the project, which would make good candidates.

      Finish up by prying the assembled section off the nailers, nip the nail ends and grind flush. Plug and glue holes with red cedar, of which we have plenty of off-cuts, to make good stopwaters.

      One point to note, one lap will extend proud... it can be strongly fastened with screws and leverage applied against those... the nails only have to keep the gains long enough to get the second layer in position.

      *** NEWS FLASH ***

      Anke just came by (with pie) and read what I just wrote. She asks, "Why remove them from the nailers?"

      "Well," I pontificate, "you can't do that because... ah... um... why, indeed?"

      So simpler answer: leave them on. No spring-back, no temporary fasteners or holes. Just flip the whole shebang, and when the time comes, position and fasten the nailers (inset by side panel thickness) to the sides!

      Need I say, she's the brains of our operation?

      BTW, the mid-curves of the jig don't need fasteners... they're just there to keep the ply honest (prevent saddling).


      So there's our latest evolution. Stay tuned for results!

      Dave Z

  2. You may find, Dave, that the curved fore and aft laminated sections, once taken off the molds for them (if I understand your plan aright) will want to "spring out" somewhat from the curve you've set in the jigs (in other words form less of a curve than they did when on the jigs). This may not matter, of course, for several reasons, but it's good to know stubborn wood sometimes does this sort of thing.

  3. Whoops! I just noticed somebody said that. For some reason the make-a-comment box loaded before the existing comments.

    1. That, or my run-on answers buried it in all the blah-be-dah! 8)


  4. This is pretty much how I built the bottom panels on my boat. Two layers of 3/4" marine ply glued and screwed together. Used stainless screws. I used gorilla glue. Maybe not the strongest of glue, nevertheless I consider strong enough because there is a huge glueing area and little stress. The panels, are 10" x 4" , 1 1/2" thick. The screws are 30mm long, slightly counter sank. I drew a grid on the sheets 6" apart, a and put a screw at each intersection. Also drilled screws holes along the edges where the panels were going g to be glued and screwed to the sides of the hull, also to be able to screw and glue panels to each other....a bit more to follow in a moment...

    1. Hi Joel,

      Question for your follow-up... How many ounces of Gorilla Glue are you using per sheet? I seem to recall an 18oz bottle with a little left over... that close?

      Dave Z

  5. The computer has benn playing up last few days...My glue comes in litre bottles, I think it was working out at about 400ml ish, per panels.
    The curved panels at the front end did straighten up a bit, but i had givrn thrm a bit more curve to start with, I think it was an extra 3/4"inch on the 8' lengths. I glued them up on top of the athwarship beams, (the beams are parallel sided) and added the 3/4" at one end to give the extra curve to account for the straightening up. I just got another 3 panels to make soon to finish the bottom of the boat...groan!

    1. Hey Joel,

      Thanks for the info on Gorilla Glue usage! That squares with my memory.

      We get GG in 36oz and 18oz (or less, but not cost effective). 400ml comes out to about 14oz.

      So, a bit less than half a liter or 36oz per panel of ply laminat.

      Good info on the overbending, too.

      And it does get tedious, dunnit?


    2. Yes it does get tedious. I'd quite like to get to enjoy this boat before I start having to shuffle around with a zimmer frame!

    3. Luckily, DIY is therapy, of sorts... may help stave off that walker!


      Dave Z

  6. [Posted on behalf of JOHN]:

    Hello Dave,

    What is the purpose of the "underlayment (for Copper)" that you have listed in your bill of materials?


    1. Hi John,

      I've wondered that myself.

      Traditionally a wood hull was finished with 'black varnish' (recipe seems to have been lost... today, some use mix of turpentine, pine tar and Japan drier... I might throw in some tung oil), and covered with Irish felt (heavy wool or flax felt saturated in tar). Some slather tar before and/or after the felt. Then copper.

      My guess is that this waterproofs the hull and gaskets the fasteners for the copper. Certainly the MIMI (100+ year old schooner we saw recoppered) looked dry and bright when her old copper/felt came off (no sign of either black varnish or tar, other than a bit from the felt).

      We've used gluey polyurethane paint, before, which seemed to work out okay. But it's expensive, and takes a lot to make the gasket.

      While shopping for Irish felt (which has become rare and expensive) a boatwright friend suggested self-adhesive roofing underlayment, which is apparently the current, professional gasketing material between timbers, for mounting hardware and such.

      A scrap was lying around, so we tried it... it's in its third week hanging in the drink, still with good adhesion. Seemed nice and easy to apply and relatively cheap.

      The brand we're ordering is Grace Ice and Heat Shield.

      Here's hoping!

      Dave Z