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 abargeinthemaking.blogspot.com), 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.