|Why concrete and box barges go together?|
You say to a brick, 'What do you want, brick?' And brick says to you, 'I like an arch.' And you say to brick, 'Look, I want one, too, but arches are expensive and I can use a concrete lintel.' And then you say: 'What do you think of that, brick?' Brick says: 'I like an arch.'
Getting Concrete... Sorta
In the never-ending search for cheap yet robust materials, concrete keeps popping up.
A boom in ferro-cement boats (concrete hulls built around a steel frame and mesh) left a mixed impression. Poorly made boats crumbled from their first days... water infiltrated the concrete and the steel bits rusted expansively, breaking up more concrete... and repeat. Well made vessels from that time can be told at a glance; they look great, structurally (cosmetics can challenge any vessel!).
But I'm more interested in wood-cement composites... the hull substantially wood, with cement or concrete playing supplementary roles.
Once again, I'm short on personal experience, but here are some evocative stories:
- One fella wrote that, in the plank-on-frame boats he'd seen with internal concrete for ballast, he noted that the hull never had any rot issues below the concrete level (alkaline environment). Frames would rot right at the surface where bilge water collected and sat. He suggested fairing the concrete up the sides and, over a number of years, had had no more rot problems in that area.
- Another remarked that in his years working with concrete, wood or tools that had been splashed with cement slurry and not cleaned up were extremely difficult to break free, later. If he did make the effort, the wood was invariably bright and tools invariably shiny under the cement (I can personally attest to this).
- Samson (a leading ferro-cement design and construction firm) developed a method for planking up a hull as a permanent male mold, to the outside of which ferro mesh was stapled and cement sheathed for a fully composite hull.
- George Beuhler was an advocate of ferro-concrete keels for us cheapskate builders. He'd up the density with boiler plate punchings, tire leads and spent sand-blasting shot.
- Greame Kenyon of New Zealand has built and lived aboard small NZ Scows (near-box barges, but with the bottom Veed forward and brought out to a point). He has decades of happy experience sheathing his scows to above the waterline with ferro-cement. His method is a couple of layers of wire mesh affixed to the hull and finished with concrete to from 1/4in to 5/16in (6mm to 9mm-ish). It protects the wood chemically and mechanically, while concentrating its weight low in the hull.
- Some exciting developments involve fiber reinforced concrete in which a whole array of fibers (in random strands or fabrics) are employed.
- Phil Bolger suggested an internal ferro-cement slab (faired up the sides as per the first fella) to stiffen the bottom, provide ballast and a well sealed bilge.
Taking all these snippets together, I wonder if one could:
- Sheath the hull to well above the waterline with ferro- or fiber-cement.
- Thicken the bottom sheathing at will to provide ballast and grounding protection.
- 'Paint' as much of the hull as desired with a fibered cement slurry for rot protection, inside and/or out.