Inflatable concrete boat?

[Will Fraser]

Just found this interesting video which immediately set the wheels in my head turning.

It is basically a cement impregnated cloth of some sort which, when soaked with water, sets like the plaster of paris used for fractured limbs. Besides the ease of construction, consistency in thickness and weight control that might benefit a ferro-cement builder, it also made me wonder about the need for steel if a suitable reinforcing "fibre" can be substituted.

As I understand it: the cement and steel mesh in a ferro-cement hull fulfills much the same purpose as the resin and glass fibres in a composite structure, respectively. The difference is that with ferro-cement, it is the steel mesh that is the "weak point" as far as maintenance and longevity of the structure due to rust, while in a GRP structure it is the resin that is the weak point due to UV degradation.

Hence my question: has it been attempted to build a glass-reinforced-cement boat? And would it indeed be as maintenance free as it appears, i.e. no UV or rust protection necessary?

I hope this video embedding works...

https://www.youtube.com/watch?v=Vb1pdvvoVoQ

 

[Russ Kaiser]

Interesting Stuff Indeed. OK, just stream of conscious here:
1.The military's pockets are deep (because they get their hands in your pocket before you do) this stuff is probably not cheap.
2. Is it available in different "gauges"?
3. Seams in a tent do not need to be as strong as seams in a boat. If you were going for a "panel" type of boat construction, would you sew them together and when wetted would the panels naturally stick to each other?
4. What's the longevity? The military may have asked for a product that would provide temporary housing for a couple of years max.
5. Is it waterproof? Just because it can survive a thousand wetting and drying cycles doesn't mean that it can live in the water.

 

[Will Fraser]

I know little enough about the ferro-cement building process and even less about this new cloth, so this is strictly exploratory, speculative, "what-if" brainstorming.

Regarding your questions on guage and seams - if it can be applied in diagonal layers like cold-moulded plywood, then neither of these concerns need be a limitation.

 

[hambamble]

Cement is strong in compression, its why they make buildings out of it. Pull on a piece of cement and it comes apart. Not great in tension.

Steel bars are great in tension, think of rod rigging that takes huge loads. Try and compress it and it buckles easily. Its crappy in compression (in rod form at least)

Ferocement boats use both these materials for their different properties - cement for compression, steel for tension. Both of these forces are active in a hull of a boat. Now, in a building like this tent, there will be a lot more compression than tension, so they can get away with less 'tensile strength' structure

If you reinforced this with a strong rope rather than a cloth, or better yet, a wire, it would probably work quite well. As for why you'd want to do it on the other hand, I have no idea. Might be a good military tool for makeshift docks/jetties.

 

[ondarvr]

I'm not sure where you got idea UV was the big downfall of polyester resin for long a lived hull or deck, but with all its shortcomings UV degradation is not one near the top of the list. It's a non issue.

 

[Rurudyne]

I've seen the video before.

At the time I wondered if the developers thought a quonset hut was somehow too luxurious to bother with the expense.

Granted this tech is still in its early stages.

For marine construction perhaps what might help (some, no confident how much) is to inflate the balloon inside of and against a matching female mold. Alignment of the two is then the issue if it works at all.

Another option might be to dispense with the balloon entirely and apply the panels over a male mold, probably one with developed surfaces.

 

[Will Fraser]

Yeah, the inflating bit is more appropriate to this quick-hut-on-site than boat building.
It was more the material that got me thinking.

 

[Rurudyne]

Also be good for the odd joke. Like turning some guy's jeans into self standing pants.

 

[tom28571]

I'm not sure where you got idea UV was the big downfall of polyester resin for long a lived hull or deck, but with all its shortcomings UV degradation is not one near the top of the list. It's a non issue.

Having seen much degradation of FG structures in the open in southern climates, I can say that UV is definitely an issue with polyester and epoxy resins. Maybe not the greatest issue but an important one nevertheless. Boats are protected by highly pigmented gelcoats and other stuff need a good UV paint. Without some protection, the resin just seem to go away, leaving the glass matrix exposed.

 

[Mr Efficiency]

The problem with glassfibre mixed with concrete might be the alkaline nature of the cement, and the resistance of glass to it, over time. Just guessing here, but I doubt "cheap" glass would do the job, or it would be used in place of the now-banned asbestos in building sheet, instead they now use cellulose fibres, (?) I think. And that certainly is not suitable for immersion.

 

[hambamble]

Why not use the same concept for carbon prepreg? I assume it would only have high end use (thinking military) but if you could pop a fleet of landing craft out in 24 hours... man, that would be a huge tactical advantage. You could even have an engine/prop built in and the boat inflates around it.

 

[Will Fraser]

An interesting entry in Wikipedia:

http://en.wikipedia.org/wiki/Glass_fiber_reinforced_concrete

It seems steel is still the final requirement when real structural strength is required. I suppose it also depends on the type and direction of the load, especially whether the load changes direction completely. For a single direction load, you would have thought that a panel with the bulk of the glass fibres to one side (for tension) and more cement on the other (compression) would have been sufficient for structural purposes.

 

[Skyak]

I know little enough about the ferro-cement building process and even less about this new cloth, so this is strictly exploratory, speculative, "what-if" brainstorming.

Regarding your questions on guage and seams - if it can be applied in diagonal layers like cold-moulded plywood, then neither of these concerns need be a limitation.

I did quite a bit of noodling about the use of high strength concrete in sailboat design. To my calculations it works. My approach was to use high strength concrete to a little above the waterline, then use less dense materials for the superstructure and a modern aluminum or CF rig. For reinforcement I used basalt fiber -stronger, rougher, denser than glass. The only structural steel would be a longitudinal compression rod, keel bolts and the rim bolts to the superstructure. My thought was that the superstructure could be wood over metal frame, the designs could be any of the golden era classics (bolt on overhangs, not concrete) and the result would match the performance of the original, but at much lower cost and far longer life. My original thought was to make a female mold in sand treated with casting chemicals but today 3D printing has come so far you could just print over a crude sand or plywood male mold. The head that dispenses the concrete also applies the fiber reinforcement so it wouldn't be a standard 3 axis Z build -at least 4 DOF likely 5 and the build would add thickness, running in different directions with each layer.

So if the result is so great why doesn't everyone/anyone do it? Because of what I call "Rudolf the red nosed reindeer syndrome". Because it IS better nobody will let it play any reindeer games. Maybe some foggy Christmas eve...

Forget about this inflatable concrete hut -wast of time. Look at concrete canoe racers (most civil eng. schools do them), high strength prefab concrete buildings and foundations, concrete 3D printing and basalt fiber.

 

[Jamie Kennedy]

For sustainability it would be nice to come up with renewable and/or recyclable material for building boats, other than wood of course which is wonderful stuff. Hemp fibre makes a very good replacement for glass, but a renewable and/or recyclable replacement for polyester or epoxy resin hasn't really been found yet. Linoleum boats don't really cut it I'm afraid, but I think we might get there eventually with some sort of natural or synthetic thermosetting polymer that holds up to moisture but can still be recycled somehow.

 

[Mr Efficiency]

For sustainability it would be nice to come up with renewable and/or recyclable material for building boats, other than wood of course which is wonderful stuff. Hemp fibre makes a very good replacement for glass, but a renewable and/or recyclable replacement for polyester or epoxy resin hasn't really been found yet. Linoleum boats don't really cut it I'm afraid, but I think we might get there eventually with some sort of natural or synthetic thermosetting polymer that holds up to moisture but can still be recycled somehow.

Polyethylene would be recyclable, presumably ? Seems to have it's admirers as a small boat building material.