Ferro-Cement boat stats and new country projects
May 26, 2008 at 5:09 am #517
At http://portlandyachts.org/portlandyachts/portlandyachts_3.html you can search 57,000 boats for sale. Of these 33 are Ferro-cement. All of the ferro-cement boats were built prior to 2000.
New country projects seem to often like ferro-cement or seacrete. But real boat builders don’t seem to. I advise caution. My own experience with cement is that it cracks. Cement cracks in boats are a much bigger problem than cement cracks in driveways or buildings.
We made a hole in a concrete roof to get a sat-tv wire in. We had trouble making it watertight afterwards. I would not want to have to make a crack in a cement boat watertight. Patching fiberglass or steel is not bad and they both have good tensile strength and don’t crack. Leaks are common in cement dams. Making a watertight patch to a crack in a cement cistern is also a hard problem.
Now a spar buoy is a bit like a submarine. Nobody ever built a cement submarine. Cracks are really bad on submarines. At the higher pressures water comes through cracks faster. In a submarine or spar buoy the extra weight of water coming in is going to have a bigger impact since flotation and weight are sort of in balance. A big ship can easily have different compartments where water going into some would not threaten the whole ship. Not sure this would be so reasonable on a small spar buoy.
I think Iron or steel down below and fiberglass on top would be more in line with established “best practice”. The professionals who design or build boats seem to avoiding cement. I suspect there are good reasons. Has anyone asked some professionals about cement spar buoys?May 26, 2008 at 8:01 am #2412
These are excellent points. I’m also not entirely convinced ferro-cement has the claimed advantage of easy, cheap, construction by a home-builder. With some solid designs, I think a home builder could more easily learn to weld decent seams and work with steel. Cement greatly benefits from being poured all at once. With steel it doesn’t matter when you weld the next piece on, as long as the material itself has not deteriorated.May 26, 2008 at 2:41 pm #2435
The FAQ has a few points on this topic.
The answer is that ferrocement has a poor strength:weight ratio, hence is poorly suited to mobile applications like ships. Most marine structures are mobile and care about weight.
Maybe that is all and maybe there is more to it. If you could build cheap boats that moved slower because they were heavy, you should at least be able to corner the live-aboard market with concrete and nobody has.
However, non-mobile marine structures, like piers and docks, often are made out of concrete. So are some oil rigs, like the mammoth
. So it’s not that ferrocement perfect for everything, just for large, non-mobile marine structures.
It looks like in Troll A the concrete only had to be water tight while they towed it into position. For them a few cracks over the years may not matter at all. Floating concrete piers and docks get flotation from foam. Non-floating ones are not too bothered by cracks either. You can buy re-bar coated in epoxy so that it won’t rust even if there are cracks. So either way cracks don’t matter much for piers and docks. So maybe the problem is not weight, maybe the real rule is, “if your marine structure is ok with cracks, then concrete can work for you”.
PS I can’t seem to get paragraph breaks. Extra blank lines are not working for me. What really works?May 26, 2008 at 3:09 pm #2440
Seasteaders will not make the mistake of counting on an impractical technology to make their vision happen. Our concept is a big enough jump already, and the fewer jumps we make along with it the better. So while necessity has prompted some novelty in our designs, they are firmly rooted in standard engineering techniques.
I think this is very sensible. I am not convinced that concrete for marine structures that need to be watertight over many years when faced with high water pressure is firmly rooted in standard engineering.May 26, 2008 at 7:14 pm #2449
Not sure what you think of the UN, but the FAO speaks to some of the concerns you have listed:
It may well therefore be asked why ferrocement has not been used more widely? This is due mainly to three factors: bad publicity due to poor amateur and professional construction; publication in the early years of outlandish claims for strength and low cost of construction, which in some cases could not be substantiated; the heavy rise in labour costs in industrialised countries which affected what is generally speaking a labour oriented material. Although today with the range of building techniques for ferrocement expanding, the labour cost factor need not play such an important part.
The website might be a good resource in general. For instance, it has info on joints and repairs in ferrocement. BTW, it doesn’t seem that the techniques of ferrocement boatbuilding recommended by the FAO are well-suited to epoxy-coated rebar: the steel they use is mostly a 1mm-diameter welded mesh.
JoelMay 26, 2008 at 9:10 pm #2457
Those are interesting references.
- bad amateur and professional construction
- outlandish claims for strength and low cost construction
- labor costs in industrialized countries
I am not sure we have overcome those things. Still not a lot of ferrocement experts around. Not sure we have the strength right, in particular when under high pressure at the bottom of the spar. I think high pressure water will help grow cracks. Labor costs were an issue in 1995 for ferrocement. Now the shipyards in industrialized countries have robots cutting and welding big plates of steel. This could skew things even more in favor of steel ships. I wonder what a shipyard would charge for a steel http://sio.ucsd.edu/voyager/flip/ Flip Ship today if we ordered 10 of them. Amateur construction and deep ocean seems like a bad combination.May 26, 2008 at 9:37 pm #2458
“Amateur construction and deep ocean seems like a bad combination. “
- While I agree withyour other points, I must say that intelligent amateurs have made a lot of humanity’s progress over the years. Don’t get trapped into thinking that university degrees and traditional experience are the only thing that matters.
- When such a person (particularly experienced, not just degreed) says something constructive, we should listen. When such a person says something negative and backs it up with facts, and calculations, we should definitely listen.
- When such a person dismisses something because it’s never been done, that’s when we should nod, smile politely, and go do our own thing.
“Amateur” means someone who does something for the love of it. It doesn’t have to mean stupid, incompetent, or even inexperienced. There are plenty of amateur pilots- they do it for the love of it, not for profit. There are many more amateur sailors. It doesn’t mean they don’t know what they are doing. There are amateur racing enthusiasts who build rocket cars and set the world’s land-speed records.May 26, 2008 at 11:35 pm #2460
I meant like the 3rd definition in http://dictionary.reference.com/search?r=2&q=amateur
” a person inexperienced or unskilled in a particular activity”. I have a friend here in Anguilla who decided to build his house using a method that had not been tried before on this island. It involved putting up these foam panels that had a wire mesh on them and then spraying on concrete. http://en.wikipedia.org/wiki/Shotcrete Well, the guys doing it had some training but they did not do it right. The concrete needed to fill in behind the wire mesh so that the wire were totally covered and sometimes they only had it on the front of the wires. In the end it cost a lot of extra money to fix things up. Anyway, I am all for experimentation and new designs. I will be posting about a design I built this past weekend after I try it in the waves this next weekend. But if I ever build a full sized one I would want to hire people who knew the necessary construction methods to build it.May 27, 2008 at 6:35 am #2466
I believe we’re on the same page. I just don’t want people to become discouraged because they have never personally built an aircraft carrier before.May 27, 2008 at 12:19 pm #2474
May 27, 2008 at 12:56 pm #2475
- As a general rule, if something has never been done, there is reason to do it (unless it´s something completely crazy, like reinforcing concrete with boiled spaghetti). Only then will you know whether it works or not.
- I think we can assume that regular reinforced concrete (as used for houses etc) probably won´t do (because of cracks). I think fiber reinforcement (plus rebar) is the way to go.
… for projects with a shorter designed lifespan.
May 27, 2008 at 4:58 pm #2494
- The Maunsell Forts were designed to be scuttled in a controlled fashion.
- It’s quite possible that a Seastead could be designed of ferro-cement to be towed to a place and moored for a period of time, perhaps while other preparatory activities were taking place and infrastructure was being built, and then, when their integrity was nearing failure or suspect, scuttled or dismantled to be used as part of a growing infrastructure.
- Perhaps a ferro-cement barge (not necessarily a spar) would be a staging platform to work on building and installing spar platforms, and then used as a breakwater.
- Such a barge could well be designed with such an end in mind that would enhance its efficiency in final phase even it it somewhat reduced its lifespan or efficiency in it’s first incarnation. Everything has its trade-offs.
November 25, 2008 at 5:07 am #4327
- I did a lot of research into boat construction materials a while back. The reason there aren’t many ferrocement boats is that it is unsuitable for boat construction. The reasons it’s unsuitable vary with the size of vessel. It IS suitable for large floating platforms as the oil industry has shown. (it’s usually poured reinforced construction not ferro cement though).
- The suitability of any material depends on the application. Develop the application (specs) first, then choose a suitable construction method/material.
- “Prosperity is only an instrument to be used, not a deity to be worshiped.”
As to the original poster’s claim that “nobody ever built a cement submarine”, the first google result for “cement submarine” returns http://www.popularmechanics.com/technology/military_law/1281166.html
If memory serves, the british once built a submarine out of ferrocrete as well. As previously mentioned, it’s not an ideal material for such uses, but I’d hesitate to write it off for all purposes based on your claims.November 25, 2008 at 9:13 am #4329
A few random points:
Pictures of a cement submarine:
One reason that ferrocement boats have not caught on, from what I’ve read, is due to the difficulty of evaluating the integrity of the hulls, which makes it difficult to get insurance.
FYI, new carbon fiber rebar and reinforcement meshes are becoming available.
Carbon fiber/concrete structures should be impervious indefinitely to salt water corrosion, without much maintenance, unlike steel or fiberglass.
Keim mineral paint jobs have endured for over 100 years, and have been adapted for marine use:
—February 2, 2009 at 12:10 am #4798
Actually,guys,most of you are wrong,…Ferrocement or ferro(as we sailors reffer to it)are DAMN good boats,….YES, if they are built right. As a sailor for 20 yrs. now I would buy a ferro anytime against any other boat. Why?Simple:wood will rot,fiberglass will blister,stell will rust and aluminum,oh well,its too expensive.None of the above w/ferro.Now for seasteading we are talking about structurelly reeinforced concrete,and its THE ONLY WAY TO GO.Why?Simple:its as strong as steel;no,wont crack that easy;its easy and cheap to built;wont deteriorate in time;its maintanance free;and,above all,IT WILL LAST FOR EVER.Dig.
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