Building a hull using Ferro-Cement

Nope, you have to use prebends, wich means you deliver a form to the factory, they lay the coated but uncured fibers on (or in) it, then it gets in the oven. Out comes the entire web frame as a unit, keeping its shape.

That beeing said, stringer-frame isn't the only way to build a ferrocement boat, regardless of what the "experts" have been preaching. Monocoque builds have been done in all sizes, from canoe to 90m ship. Ulrich Finsterwalder and the DYWIDAG rewrote the book on ferro, even if most people never heard of them.

To my knowledge only one prestressed ferrocement boat was buildt, using the poststressing method, Helsal, 22m (73ft) , designer Joe Adams, structural engineer Peter Ellen. We even have a thread about it: Helsal 1 - Adams - Concrete Racing Yacht Plan Sourcing https://www.boatdesign.net/threads/helsal-1-adams-concrete-racing-yacht-plan-sourcing.59290/ The picture in there comes from a site about the engineers work. S-squared http://www.pt-technology.com.au/home/evolution/history/peter-ellen.aspx

 

I tend to view any ferro boat as a "monocoque", whatever the framing type. The web frames for bulkhead attachments and stiffeners, was certainly common, personally I have not been aboard a ferro boat that was not built in that way. Interesting link!

How do you join together balsalt re-bar? At least with the steel, it could be welded.

 

Most ferro boats from the golden age were semi-monocoques, the web frames and stringers were the primary load bearers. A monocoque can have stiffeners, but they are calculated for local loads, only the bulkheads (if present) are primary transverse members.
I suspect some designers weren't familiar with more advanced concrete concepts, and others tried to make it as accessible as possible for the amateur.

A common myth is that without a wooden mold it isn't possible to spray concrete, altough in fact it has been done since the 1930's using a removable 4mm mesh. The use of lightweight expanded clay aggregates (sintered clay) was pioneered in the 40's, the resulting 1700kg/m3 concrete was overlayed with a thin layer of very hard concrete formulated for abrasion resistance. The hull was then mechanically polished. Small ships of this type (Seeleichter Wiking Motor, 337 dwt) built in 43-45 were in use well after the war, one example was struck from Lloyd's Register in 1978, there are at least four known floating survivors, and a few wrecks. Reportedly their biggest flaw was the insufficient power (2x150hp, V12 diesels from italian tanks) and to small rudders. I'll atach photos of the launching of one so you can appreciate the workmanship. In contrast the superstructure still sports the wood grain imprint of the mold.

Joining composite rebar is done by overlapping, the ties (zip ties or coated wire) offer no mechanical strength. Basically the same thing as with steel (welding reinforcements on site is often prohibited).
In theory epoxy glueing (with or without additional reinforcement like tow) is possible, but that has to be cleared by the manufacturer since most coat their products with an adhesion enhancer. I have never heard of someone doing it, but I'm not an expert in the field.

 

It looks like materials have certainly come a long way that could be used in a modern hull build, but with increased costs. I cant imagine a designer today attempting to push a "new" system using cement, unless im completely unaware. It was always claimed to be the cheapest way to build a hull.

 

NO, it might be cheap, but so is a wooden coffin !!! The only way to correctly survey a Ferro jobbie is to drill a bunch of holes into it to see if the rebar has rusted. If you want to do a safe Ferro, use stainless steel, not mild steel, OR, get all the rebar heavily hot dipped galvanised. Alas I doubt if either technique will help with an insurance survey, as it would be very expensive to get full agreed hull loss value included with a basic 3rd party policy.

So do a proper job, or suffer the expensive, (Canals, rivers and lakes), type of failure that killed a South African couple a few hundred miles South of Madagascar, as they had an old cheap Ferro ketch, but there was a real big rolly polly swell reported in the area that disappeared crossing. An Epirb signal was reported on 121.5 Mhz by an South African Airways, BUT by the time the recue aircraft got near their area, the signal had stopped. Not a good way to die, so think about some serious safety gear, like a 6 man Switlik toroidal raft.

 

There is fiberglass rebar or carbon rebar today that can and should replace in a Ferro cement boat build .

 

That type of rebar can't be bent to shape. It would be extremely expensive to manufacture bars to the shape of a hull.

 

#3 or 4 fiberglass rebar can be bent to some extent , I don't think bow to stern on a hull would be any problem , or on bulkheads . A sharp bend would be a problem and would have to be custom , and would also have more cost than say a 45 degree fiberglass corner bar or other angled bar used in regular concrete construction calling for fiberglass or carbon rebar . While various coatings on rebar slows the start of rusting of rebar , once coated rebar starts rusting , it rust faster than non coated . You will still see it used in some building on coastal builds , but I have never seen it used on a single condo on the beach I have worked on , it is old Tech .

 

Epoxy coated rebar is commonly used in road and bridge construction. However, it can't be bent too much or the coating fails. Also, after cutting it should be re-coated.

 

gonzo , there are some Engineers still calling for coated rebar , also some States tend to be behind the times on new concrete mix designs or other structural design developments , it,s worked for 100 years . Got out of high rise work in 08 and went back to work for a Bridge company , retired from that company , I never used any coated rebar on a road or bridge I worked on in Al. Ms, or Fl . That is not to say it is not used in a design depending on the State or area of the State . We tried to get a concrete mix design approved on a bridge in Al. with no luck , there was a bridge damaged and the repair required that the concrete could be driven on after 24 hrs , the inspectors on our job worked the repair job and came back amassed at the repair mix , same mix design we tried to get approved .

 

In Wisconsin the tie-bars and dowels at the cut joints are all epoxy coated. It is a requirement by the State. However, each County can vary some specifications. For example, when we did the new I-43/94 highway, Milwaukee county requires 13" thickness pavement, but Racine county only 12".

 

States tend to take the position that it,s has always worked and it will keep working , they are not interested in change unless they have to . Florida went to super girders years ago that increases the span,s and reduced the number of bents , it hasn't caught on here in Alabama . The Feds let us use an admixture ( Master set from Delvo ) that put the concrete to sleep for around 18 hours , 1st trial batch was closer to 3 days . There are just so many more options today .

 

I am not familiar with that product, but sounds really good. On hot days we give the dump trucks 55 minutes from loading the concrete to dropping it. Concrete companies are forced to set field readymix factories along the road.

 

That product will make you have good days gonzo , psi will increase , the 1st test batch was a 5000 mix , I could press my thumb in the top of the cly after 3 day,s , 7 day break was 11,000 .

 

Amazing! Speaking as an old Combat Engineer