Ok everyone, it's that time of the year again: time to talk about concrete

I work with glass fibers, no steel, and special premixes (no water) for very high strengths. I am not an engineer though, I just judge by how a material feels in my hands or when I step on it.

As to missing the point, I suppose it depends on the person, I would never buy a sailboat that couldn't sail, actually I wouldn't even accept one as a gift
But I guess if it was a charter boat that was just going to motor around with a sail more for show than for propulsion, then it might appeal to some.

 

A material that was in fashion for balcony flooring here was "compressed fibro", which was asbestos reinforced cement, going by the name of it, was subjected to compression which gave it a slick smooth, impermeable surface that would not hold ordinary paints, but needed an epoxy primer. The panels were 1/2" thick. That would have been at least twice the weight of a ply panel that would have done the same duty.

 

The properties of concrete have been documented and understood as posts, beams, slabs and mortar, not as thin laminates. That's sort of the point of the college paper wasn't it, to document a new thing?

I don't think industry is all that conservative about new ideas. It is competitive though, and if you come up with a better idea, industry will steal it and use it PDQ.

 

Well, that's why I chose it, but most of the paper topic were fairly mundane. And yes, it's definitely "new" from a thin laminate perspective. But that's a relative term. "New" in civil engineering terms is 20 years. Thin laminates are actually what it's used for: facades are one of the main uses (it has superior abrasion resistance). But your broader point that it hasn't been used in boats is noted. It just seems to me to be a chicken and egg scenario, and largely overshadowed by what's being done with foils and various carbon fiber type things. Thing is, I don't find those interesting, from an engineering perspective. "Make it out of carbon fiber" may be "new" (I realize there have been race boats made of the stuff since the 80's, but it really has hit the public mindshare in a way it hadn't previously) to boating, but it's not exactly mind blowing. Great, you can make a $100 million boat that can be sailed by a crew of 3 and do 35 knots. That's got as much to do with the average person cruising as Ferrari winning a constructor's championship does with my next minivan: nothing. Even at today's much cheaper prices, it's still the material of the 0.01%. If I can afford the keel of a 40 foot boat in carbon fiber, or a whole 40 foot boat in FGRC, then I'll opt for the one I can actually get a whole boat out of.

As for being conservative: look how many guys still swear that monohulls are safer, despite all evidence to the contrary. It took almost a century to unban a clearly superior design just because it was clearly superior (as opposed to being more expensive).

 

Plywood doesn't have anywhere near the abrasion resistance of granite, which is the closest material analogue for UHPC. And painting it is a somewhat odd choice: you can stain them just about any color you can think of, and then use epoxy to seal it. Or mix the pigment straight into the concrete itself. Then it doesn't really discolor.

 

The member below posted about this stuff and thought it would make a boat...

Concrete Cloth GCCM :: Milliken Infrastructure http://infrastructure.milliken.com/concretecloth/

concrete cloth - Google Search https://www.google.com/search?biw=1366&bih=628&tbm=isch&sa=1&q=concrete+cloth&oq=concrete+cloth&gs_l=psy-ab.3..0l4.24913.30561.0.31323.14.14.0.0.0.0.201.1712.3j10j1.14.0....0...1.1.64.psy-ab..0.14.1705...0i67k1.0.cvi0gfAKdD0

mustafaumu sarac
New Member from Istanbul

 

There's a concept that floats around the startup scene similar to "minimum viable product." It's why smartphones have largely replaced point and shoot cameras and camcorders: they work "well enough" and are readily available. I think it applies here. So my question is: how fast is "fast enough"? Half the apparent windspeed? I'd bet money that's easily within reach (if I had money...). You want to do eight knots in a 40 foot catamaran? Done. Easy. You won't carry as much payload as a 40 foot glass cat, but you'll carry a hell of a lot more than the 30 foot glass cat that's the same price.

 

Weight doesn't matter on a balcony that much, on most boats it is a critical factor.

 

That's fun looking stuff. The only thing I wouldn't know how to do is join it. I suppose in theory it should adhere to itself if you peeled the PVC backing off, but I'd probably want to know more about what the fiber matrix was. Assuming you could figure out a way to join pieces effectively, it would be a really freaking fast build. Like hours for the main shell (still your month of curing though).

 

Well, two points there. First: you can't consider the strength without considering the cost. That kills the top two contenders (foam core and glass), and leaves plywood, which it is also cheaper than by a wide margin. Practically speaking, this means I can make a hull that would be prohibitively expensive in plywood or glass (e.g. a long, slender catamaran) instead of a short, squat monohull for the same price.

Second, the tensile strength of UHCP is about 10% less than mild steel, pound for pound (using 1-2 inch steel fibers as the reinforcement). But the compressive strength, obviously, is much greater.

 

There are other teams that cure for longer. The competition, as you might expect, is as much (or more) about the demonstration of the design process as it is the finished product.

Here's the page with all the papers (well, probably more than anyone has the patience to read, I've only perused a handful of them):
Wisconsin Concrete Canoe - Design Papers http://canoe.slc.engr.wisc.edu/designpapers.html

The biggest difference between the race and what I would expect a boatbuilder to use is that the teams pretty universally seem to use carbon fiber trellises for the frame. On a 20ft canoe, this is a pretty small expense, but on a much larger boat I expect it would be prohibitive.

 

It doesn't need to be on the mold for 16 days. It hardens enough to demold within a few hours to a few days, depending on whether you use nothing, or set retarder or set accelerator. It just continues to gain strength after that. Although, to be fair, it does best if you let it cure the full 28 days in a hot (100C) humid environment. The strongest precast stuff stays in what amounts to a steam room for that time. For us peasants though, as long as you keep it moist and insulated (the reaction is naturally exothermic) you'll get a pretty good result. And in that time you can flip it and put the deck on, etc. As long as you're not taking it off the mold and tossing it in the atlantic, by the time you've got everything else fitted, it should have cured just fine.

 

A 21' canoe weighing 160 lbs compares to how much weight in a typical one that size ?

 

A grumman 19 ft aluminum canoe is 119 lbs. It looks like the polycarbonate canoes don't get made that big, so I don't have anything to compare there. The closest I found was a 15.6 foot that weighs 95 lbs. which gives 126 lbs for a 20 ft. I suspect that number is low though, as extending the hull an extra 5 ft would require significantly more reinforcement. I also found a 13 foot canoe that was 96 lbs which would gives a weight of 155 lbs at 21 ft. In any case, the aluminum hull gives a mass of 34% heavier than aluminum.

MACKINAW https://www.sundolphin.com/mackinaw
Lifetime Kodiak Canoe : Cabela's http://www.cabelas.com/product/boating/canoes-kayaks-small-boats/canoes-kayaks/pc/104794380/c/104710680/sc/104252580/lifetime-kodiak-canoe/2278690.uts?slotId=2

 

You need to get your head around some engineering before wandering into the deep end of the pool. Concrete isn't commonly employed be cause of elongation modulus and weight. Even the new stuff with its much improved modulus, just weighs way too much for the modern sailboat and performance orient power cruiser, let alone anything at the small end (30' or less) of the pleasure boat market. Cost be damned, if the stuff is too heavy. Plywood is considered heavy, so cored structures, which cost 3 and 4 times as much, are employed and you think concrete is a viable answer? Run it past an engineer first and see where you stand after the evaluation. My point is this isn't something new, about once a year, someone comes along and "discovers" ferro or attempts to justify it it. The analise has been done previously and found wanting in several regards.