new way to build concret hulls?

http://www.youtube.com/watch?v=Vb1pdvvoVoQ&feature=player_embedded

 

That is very cool.

 

A lot better than I initially assumed.
Now all you need is some steel mesh to take the tensile loads, or do you?

The nice distributed load of holding itself up is a lot different from boat loads.
Who is the first guniea pig?

 

The steel mesh is probable the thing holding it together. And it doesn't need to be steel, Just anything that takes up tensile load, FG would do fine for some applications

 

Interesting for shelters but it lacks the strength needed for making hulls which ask for a strong dense steel mesh and structure. Concrete hulls are a composite of steel wires embedded in cement.
It's unable to take the shape of non developed surfaces. I suspect also that the used cement/aggregate does not meet the requirements for marine ferro cement structures.
As always with ferro cement, it will be too heavy for its strength, and a felt won't help. How to take out the air bubbles for a dense waterproof hull surface?

 

I remember reading about this around 5 years ago and it's not light around 2 pounds a square foot for 1/4" thick material. It also can prove difficult to make water tight joints. Currently they wire tie it, often over a steel armature, glue it (lap joint and epoxy) or grout the seams. Certainly lighter than more conventional concrete systems, but seams would be problematic. The material is available in relatively narrow widths too, so seams are mandatory.

I don't know much about it's dynamic stability (wouldn't expect it to be very good, without an armature), which would be paramount in a boat, but I could see barges and some work vessels being built from this stuff. Lastly, you'll need one tough *** mold for this stuff, which would drape well, but will be 2 to 3 times the dry weight, until fully cured.

Some clever molding, with up turned flanges at the seams, that also form stringers is something to explore.

 

There you go, being all practical and everything. And here I was pontificating about something I know very little about, even though my engineering school was a perennial winner in the concrete canoe competition

 

As always with concrete the behavior with variable loads is rather bad (remember the electrical concrete posts that fail miserably under the buffetings of a strong wind). The main problem with a felt is to get rid of a micro bubbles of air, not a problem on a short lived canoe or a 10 years shelter, but it's a big one on a boat staying permanently in water. It's almost impossible to compact. Besides as I have already said the ratio weight/strength (specially flexural) is really too bad. Ferro cement is just good for barges.

The 28 days delay for a fully hydration is also another problem, unless curing with steam. Plus the delay for drying the stuff. Plus the cost of the epoxy final coats.

If ferro cement was a so good material, we would see thousands of boats (at least cargos and fishing) made in this material; it's not the case. And finally when you make the calculations of cost of the finished product, it appears to be rather expensive compared to polyester or steel at least for work boats.

 

Over the years I have given some thought to high strength cement use in the hulls of sailboats. My case for it's use would be based on two premises, 1 long term the cost of upkeep for cement underwater is good in areas above freezing and well documented and 2 the weight factor of performance in a monohull is about proportional to the square of the height from the waterline. Carbon fiber makes great sense for a mast, lead make great sense far below the waterline.

My thought was to make classic designs with high strength concrete below the waterline to a few inches above, and wood on metal frame above the waterline, with CF mast and a lead bulb to match the righting. The last factor to match is rotational inertia for and aft which might be handled with composite or wood crashbox or overhangs. Classics are still desirable but the cost of new builds in wood and the cost of upkeep are crazy. Most of the difficult expensive woodwork is hidden below the waterline and that is also where most fail and need rebuilding. High strength concrete is displacing steel in skyscrapers and it can be loaded in compression longitudinally.

There are plenty of designers around with large portfolios of classic designs that could benefit from this.

 

Cement is well documented in terms of static load employment, at which it does well. Unfortunately, boats experience dynamic loads, of which concrete is poorly suited. In boats, the only real successes have been ferro builds, which in the USA you couldn't sell if you offered your first born with. In Europe and some other areas, such as Australia, the value of ferro is a bit higher, but still a very low percentage of vessel production figures, again for understandable reasons. There's no need to get into the ferro debate, as it's been hashed repeatedly here, but the numbers clearly show it's value in the market.

I find it difficult to believe that the authors of "classic" designs would even consider a hodge podged concrete, wood, CF composite build. The mere mentioning of concrete in the same sentence with CF, is a obvious oxymoron. Lets take big Ti and make her lower hull of concrete (of course with the obligatory lower hull x-rays for her annual surveys), her upper works of wood and cap with a CF ketch rig - really? How about big Ti with a carbon/spectra hull and deck, foam or honeycomb core interior partitions and furniture and a CF rig? We can use spent uranium rods (epoxy coated of course) in her keel to further lower her CG . . .

 

concrete boats

The Gulf Coast is littered with broken up concrete boats, but I have seen some that were reinforced with an outer skin of epoxy and fiberglass that were being used as house boats and small tankers. Hydraulic concrete was usually what was used by most experimenters because it was not as porous as other mixtures. But I think the worst culprit was the sea salts that migrated into the concrete over time from either the interior surfaces or just because of prolonged use in sea water.:idea:

 

I really like skyark's idea of using a lead keel, a steel reinforced concrete lower hull, wood superstructure and deck, and carbon spars. It makes good sense, it puts the weight were it is most useful, and used durable materials below the water line, and the lightweight (and costly) materials where it is most important to have it.

Modern ferrocement with high tech ad-mixtures can be made very thin compared to conventional concrete. With a number of epoxy coatings and layers of bottom paint, the hull might hold up quite well. You could even put heavy coats of sealants on the inside as well.

 

I disagree. There's just way too many new issues and several old ones that come to the table with an approach like this.

For weight to be effectively utilized, it needs to be at the end of the keel, not in the hull shell. Then there's the above the LWL joint between wood and concrete, which is always going to be problematic. Lastly, to take this to a logical conclusion, you would have a lead ballast (or uranium), CF and spectra hull and deck with CF spars. This places the weight where it belongs and is most effective, offers a continuous, seam free, monolithic hull shell and deck cap and the lightest spars. Of course this is being done, but is costly, though considerably less so than having a concrete crew, wooden element crew and composite crew on stand by, waiting for their turn at the project after the ballast is cast. Even an all wooden hull, with composite spars and lead ballast, is a better choice as the ballast ratio can be higher. At some point (size) wood becomes less viable in this regard, but there are other options that easily outshine concrete hulls.

 

I agree heartily with you Par exactly for the reasons you gave. It's "false" logic (I do not even mention the issues of joining concrete with wood and keep the joint waterproof. The typical example of a solution of continuity; joining dissimilar materials is generally a source of problems) and visibly it can be imagined only by persons without real experience of boat building. I won't mention also the dynamic problems (polar inertia and the resultant pounding for example) induced by a heavy bottom with the weight going all along a sailboat. Ballasts must be as near as possible of the center of gravity.

 

Correction: To 'contribute' to righting, weight only needs to be below the transverse metacenter which is above deck on a well designed sailboat. To be 'effective' it needs to be below the center of gravity which tends to be above the waterline on classic yachts. The wood joint at the top of the concrete is a problem that is tiny compared to the ~10x greater length wood to wood joints common in classic yachts.

The rest of your post is countering an assertion I never made -that my proposed construction method is the best way to make modern performance sailboats. It's obviously not a winner for all out performance, but how much does that mater when almost all sailboat racing is to handicap?

My assertion IS that my proposed construction would be a highly effective means of making replicas of historic designs -one offs that match the ORIGINAL CHARACTERISTICS for mass, hydrodynamics, and moments of inertia. Golden eras reconstructed at low cost and requiring far less maintenance than exact originals. The keel boat equivalent of stitch & glue 'instant boats'. My favorite is 'stormy weather' or maybe 'Dorade'.

About the reputation of concrete hulls -much is based on ferocement method which is far from kosher engineering. Bare steel in the concrete will fail. More is based on barges that are not built for the long term and not cared for. BTW Skyscrapers are dynamically loaded.

PETRO,
Thanks! I am glad you like it. Your opinion means a lot to me. There is more to it and I am realizing that I will not have time to pursue every concept I have. I will PM more when I get the chance.