ferro-cement 6 meters sailboat

[jelfiser]

hi to all ,
we are some friend and we planning to build a 6 meters ferro-cement boa, i've got some small notions on boat desing and i'm making first calculation ,
i know it should be a bit heavy but i think that with a great sail and hard wind it should move

my problem now is

i know ferro cement is 2500kg/m3 so how much should be thin the hull for this kind of boat? 1,1.5,2 cm?

also someone can tell me how much and how i have to put steel to make mesh ?

so thank you to anyone reading and exuse me for my bad english

[Raggi_Thor]

I suggest you try any other material, plywood, glassfibre, aluminium :-)

[SeaSpark]

Concrete does not necessarily need too be reinforced with steel. Plastics or other materials can also be used. See the Glassfibre Reinforced Concrete Association website http://www.grca.org.uk/ for more information.

For a boat of this length weight saving seems critical to me.

Some schools in Holland have annual regatta's in concrete canoes (less then 0.5cm thin hulls) ill see if i can find more information about them.

(edit: this type of regatta seems to be international http://concretecanoe.org/ check "click here to enter" at bottom of page)

[jelfiser]

thank you raggi tohr and seaspark,
the use of ferrocement depend from having a cheap boat with no so much intruments and molds ,so i thought the steel should gave shape.
the boat is withouth tug .
about the weight is important that the boat has a similar weight of a similar traditional eavy (and expensive) wooden boat like those

http://www.lancepantesche.com/module...showgall&gid=5

in my town they organize a traditional regata and we want some cheap alternative for pratice

it seems to me that an hull thin 1,2 cm (30kg/m2) should be quite good for weigt
what do you think about ?
thanks

[SeaSpark]

Jelfiser, the boats in the link you provided are sure good looking! It seems a good design to build in concete.

I have no experience at all buiding concrete boats but guess a 1.2cm thick hull reinforced with ample chicken wire should do the job. Hope someone can make a more calculated estimation. You could always try the trial an error way and add extra layers of concrete and reinforcement if the hull seems to weak.

[SeaSpark]

http://www.benford.us/scp/12keelboat.html
http://www.cruisingresources.com/ind...t_Construction
http://www.ferrocement.org/ (down at moment due to bandwith limitations)

[Hunter25]

Guess work in the scantlings is a fools endeavor. Chicken wire is not what you need, nor is "eyeballing" thicknesses. In reality the thicknesses will vary based on loading requirements.

You need a design that can account for the additional displacement required using ferro cement construction. This is especially true of boats under 10 meters. This same design will also address the specific requirements for the limitations of the method. The same is true when building a fiberglass hull out of steel, or a wooden boat with aluminum. The displacement must be adjusted for the construction method. Much else must be adjusted as well, such as the differing structural needs each method demands, but this will come with the plans or a revised set of plans.

There are a few books on the subject, but they are not a substitute for a proper design which uses ferro in the hull. Jay Benford wrote a good book on the subject and there are a few others.

A 6 meter boat is a might small for this method and risky considering your lack of design and building (with ferro) experience. The hull construction does not amount to nearly as much of the total building effort as you may think. In a boat this size, it will only account for 15% of the total build. Other structural issues, furnishings, equipment, tankage, electrical, plumbing, rigging, spars all take up much more time and money to build then the hull shell. Find a real ferro design or have the one you got converted if possible. You would be much better off using another, more common building material other wise.

[FAST FRED]

I have never seen a back yard concrete boat that did not weigh out at less than 15lbs per sq ft.no matter how hard they tried to go thin.

Usually the hull alone weighs what the finished ready for sea vessel should weigh.

ANY other construction method is to be prefered over cement.

The second problem is Fero can not be surveyed , so no resale value , and no insurance .

Another hassle is the hull is usually only 15% of the cost of a fully finished boat , so if all your friend can afford is the hull, where will 6X the cash to finish it come from?

Steel is the prefered backyard material, a course in welding at the local Vo -Tec skool should suffice for the required skills.

FAST FRED

[SeaSpark]

The boats from the link Jelfiser provided seem quite heavy in displacement. If a 6m concrete hull is possible this design seems a good starting point. Don't know what his calculations for the 1.2cm hull thickness are based upon but guess he took the displacement of a wooden version as a start.

The boats are nothing more then a hull with a rig. Cost balance 15%hull 85% rig would be very nice! A 4m fibre reinforced canoe has been build that weighs only 15kg.

[jelfiser]

yes the wooden boat i'm starting must be quite eavy , the boat is only a simple hull , i just have mast , sail ad keel it seem to me that the most expensive thing is the hull , i chose ferrocement as a substitute of eavy wood , as cheap and with no need of mold,
my truble is in sructure nedds consider those wooden boat are made wit 3 cm tick wood so
wood: 3cm x 800 kg /m3=24kg similar to ferrocement 1cm x 2500=25kg
wat do you think

[Poida]

I've often wondered what happened to the ferro cement boats, they made a big stir here when they started making them but the idea seemed to have fizzled out. I took that as probably the idea was not as good as first thought.

Of course then, as someone pointed out, resale value could have been an issue.

Here wooden boats don't sell well, although I love them. The good thing is you can pick them up real cheap.

Thought chicken wire would be a bit sus. mind you, maybe chicken wire in other countries may be stronger than ours ie. is the chicken wire also made strong enough keep predetors out. Ours is only strong enough to keep the chickens in. I guess you would have to be careful advocating chicken wire to someone overseas when you may not know the gauge of chicken wire in question.

Good luck with your boat.

[jelfiser]

read ,somewath interesting on concrete canoe and also find interseting this article

http://sleekfreak.ath.cx:81/3wdev/VI...1/FERRCMNT.HTM

it use a 1,5 cm but i think is inteded for a greater boat ,

also do you think that for a similar boat it is sufficent making also bulkheads or as in concrete canoe the sheel is sufficient ?

i tink to put next days the first concept and design of the boat
tanks to all

[jelfiser]

Originally Posted by FAST FRED

I have never seen a back yard concrete boat that did not weigh out at less than 15lbs per sq ft.no matter how hard they tried to go thin.

Usually the hull alone weighs what the finished ready for sea vessel should weigh.

ANY other construction method is to be prefered over cement.

The second problem is Fero can not be surveyed , so no resale value , and no insurance .

Another hassle is the hull is usually only 15% of the cost of a fully finished boat , so if all your friend can afford is the hull, where will 6X the cash to finish it come from?

Steel is the prefered backyard material, a course in welding at the local Vo -Tec skool should suffice for the required skills.

FAST FRED

i tink that 15 lbs / 8kg should be really a good weigt for my project someone can tell me more about that?

[SeaSpark]

Bulkheads will be necessary especially in places where the rigging puts a load on the hull. How many exactly i cannot tell you.

Plywood bulkheads may be an option you could "stitch and glue" them to the hull with steel wire and cement. This is just theoretical, as far as i know it has never been tried but seems a good way to keep weight down and it is easy to build.

A plywood deck may also be possible.

Of course this means the end result will be less rot resistant than a completely concrete hull.

[SeaSpark]

If you really want to build this boat in concrete i think you should use a mold.

Building a boat with this hull thickness without a mold will be very difficult. Hull shape is important not only for resistance in water and good looks, an an irregular shape will weaken the hull. I think it is close to impossible to build a fair 1.2cm thick hull in concrete without a mold. Building a mold will improve your building skills so the the final hull will be better.

It will be very easy to build a second hull that corrects mistakes made in the first. It seems to me you want your boat to race in a class, so if this works out you may want to build more hulls anyway.