ferro-cement 6 meters sailboat

[jelfiser]

Originally Posted by 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.

i totally agree with a flat /bit conically, plywood deck

surlely you're right , to have a perfect shape we need a mold,
so the questions are

female or male mold?
how much should it cost ?

i belive that making a traditional female mold should make loose of sense the idea of concrete as a cheap material

also the boat is tought as an alternative for boys to pratice to the exsisting class that wants boats made only in wood boat that are quite exclusive and expensive

so i'm just thinking... if we don't make any bulkheads but realize (once we have printed out some rapresentative section) the full shape of the boat with light ,and cheap ;-) , urethane foams, then once we sand it until it come regular cover it with a really thin layer of ferrocement we should have :

a boat lighter than a similar made of wood
unisinkable ( with no space inside but we don't need)
cheap boat
resistant ( foam adsorb well compression strenght)
easy to build with few instruments

what do you think about ?

thank you and sorry for my bad english (i hope you understand all)

[Guillermo]

jelfiser,
Maybe this is of interest to you:
http://www.fao.org/DOCREP/003/V9468E/V9468E00.HTM

[SeaSpark]

I would use a female mold.

Building one is a lot of work but making a fair hull from a male plug or no mold at all is also labour intensive. If the boat is used for teaching people to sail in this class i can imagine you want to build more then one. When this is the case the mold pays back invested time quickly. If the concrete does not work you can use the mold to make a polyester version. Material costs don't have to be to high, you can use any quality of wood and concrete for the mold.

Building a male plug from foam seems expencive to me, foam is light but not very cheap. Fairing the foam hull will be a lot of work and you have to repeat it for every boat. My guess is that concrete does not stick well to urethane foam.

Building a concrete boat in this size range will be experimental there are no standard solutions availabe.

[jonsailor]

What you need is a product called "Watsons" mesh which was a high tensile woven mesh developed for fero cement boats in NZ.
We plastered over 100 vessals in our hey days and we infact sold some watsons mesh to a university to make a canoe for a cometition which was formed fom 2 layers of mesh giving a hull thickness of about 1.1cm.
The mesh is an "I" beam section in itself giving a thickness of about 5mm.
It is vey stiff in section but can take compound curves although the uni canoes were hardchine.
Our 35-40 ft yachts had a panel weight of 12lbs/ft2 but this had reinforcing longitudinals as wells as the mesh,
We had many yachts that also performed well in sailing ability and I infact won a single handed race from NZ to Australia in about 1981.
If you are serious about this (I have moved on to carbon racing yachts) then maybe NZ is the best place to get some ideas from. My father was a big pioneer of the material in the 1960-80's

[jelfiser]

Originally Posted by Guillermo

jelfiser,
Maybe this is of interest to you:
http://www.fao.org/DOCREP/003/V9468E/V9468E00.HTM

thank you gulliermo , interesting, i'll print and study next days , but it seems to me it don't contains answers relating to a so thick hull
thank you for good link

[jelfiser]

Originally Posted by SeaSpark

I would use a female mold.

Building one is a lot of work but making a fair hull from a male plug or no mold at all is also labour intensive. If the boat is used for teaching people to sail in this class i can imagine you want to build more then one. When this is the case the mold pays back invested time quickly. If the concrete does not work you can use the mold to make a polyester version. Material costs don't have to be to high, you can use any quality of wood and concrete for the mold.

Building a male plug from foam seems expencive to me, foam is light but not very cheap. Fairing the foam hull will be a lot of work and you have to repeat it for every boat. My guess is that concrete does not stick well to urethane foam.

Building a concrete boat in this size range will be experimental there are no standard solutions availabe.

i'm quite afraid on building a mold, and i think that would be built other ferro cement boat only if it would work good,
but if you say that a female mold should be cheap i trust you, may be with scrap wood for traverse, bamboo sections logitudinally, all faired with concrete (here in italy they build in that way internal vault in ancient house)
i agree it should be cheap and not soo difficult , i'm not sure on results ,
also
those kind of boats have a steel finn kell, should became difficult once extract the faired hull, make a solid joint between hull and keel

thank you for good ideas
and sorry for my bad english

[jelfiser]

Originally Posted by jonsailor

What you need is a product called "Watsons" mesh which was a high tensile woven mesh developed for fero cement boats in NZ.
We plastered over 100 vessals in our hey days and we infact sold some watsons mesh to a university to make a canoe for a cometition which was formed fom 2 layers of mesh giving a hull thickness of about 1.1cm.
The mesh is an "I" beam section in itself giving a thickness of about 5mm.
It is vey stiff in section but can take compound curves although the uni canoes were hardchine.
Our 35-40 ft yachts had a panel weight of 12lbs/ft2 but this had reinforcing longitudinals as wells as the mesh,
We had many yachts that also performed well in sailing ability and I infact won a single handed race from NZ to Australia in about 1981.
If you are serious about this (I have moved on to carbon racing yachts) then maybe NZ is the best place to get some ideas from. My father was a big pioneer of the material in the 1960-80's

really interesting.. unfortunatly i suppose that here in italy i cannot find your "watson ", do yoy know somewath similar? i have a look on web an i didn' tfound nothing , have you any picture to giving me a better idea?
thank you

[jonsailor]

I will look into it further for you but alas I need a bit more time.
Another good alternative that we used for the budget client was welded square mesh, not the woven interlocked chicken mesh.
The welded mesh is stronger and thus you can build a stronger shape lighter.
The watsons mesh was also used extensively in doing the big skate board and roller blade bowls as well.
I will get back to you in about 12 hours.
cheers

[jelfiser]

Originally Posted by jonsailor

I will look into it further for you but alas I need a bit more time.
Another good alternative that we used for the budget client was welded square mesh, not the woven interlocked chicken mesh.
The welded mesh is stronger and thus you can build a stronger shape lighter.
The watsons mesh was also used extensively in doing the big skate board and roller blade bowls as well.
I will get back to you in about 12 hours.
cheers

tank you all for intersting considerations.

seem good the idea of using welded steel , i'm courios to know wich thickness of steel you can use in this way and how much are spacious the mesh
also you always need the mold ?

cheers

[jelfiser]

well the ferro cement surface come out 14 m2 , so i ipotize in that sketc 650 kg for displacement here the waterline and some rendering , i have still to adjust it bu i think it should look like something similar i put here some rend and wateline
what do you think about ??