Ferro Cement Cat

Discussion in 'Boat Design' started by LT Marine, Apr 5, 2010.

  1. Rummy
    Joined: Mar 2010
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    Rummy Junior Member

    Gunite

    Interesting.... I'm a lifelong builder and was just wondering if we are talking about using gunite or shotcrete for this process. Just like a swimming pool. I worked in a mine a million years ago and we shotcreted the walls so there must be some strength there. I mostly agree with the discussion on chicken wire. I've never seen it in concrete but it is used in traditional stucco. FYI standard mesh is called 6x6-10x10. That would be 6" square grid of 10 gauge wires each way. Now should any of this steel be epoxy coated? It's the norm in bridge construction now. BOB
     
  2. tugboat

    tugboat Previous Member

    Rummy- i should have been more specific- not sure if your post was directed at me-- a better term would be "hardware cloth"...it is necessary in ferro-cement to use tight spacing...you cannot go any more than holes of about 1/4 inch meaning 3 inch holes would weaken the concrete too much and it would fall apart. we are talking a hull thickness of 3/4-1 inch and the layers must produce opening no greater than 1/4 inch. the reason for this is something called diminished dispersal effect...so standard 6 x 6 mesh is not going to work... the steel should NOT be expoxy coated as the cement needs the rust to act as something to adhere to the wire mesh. ruswt is necessary in an armiture. also most builders i.e. samson, hartley and brookes, and many other designers save for Jay benford used chicken wire 1/2 inch

    hope that helps...
     
  3. Rummy
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    Rummy Junior Member

    Design Mix

    Thanks Tug. I didn't realize the hulls were so thin which explains why standard mesh won't work which got me thinking about adding fiber. I still wonder about gunite especially as a convenient form of application. At least the human mixer wouldn't be having a heart attack and there might be less of a chance for air pockets. Also what would be the required mix design in psi? Just keeping the thread going.
     
  4. Lurvio
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    Lurvio Mad scientist

    Tug
    You won't be building an 80ft barge with 1 inch skin. Rowboats yes, but nothing that size. :p

    And yes, it aint necessary to make the hull the shape I've drawn. Personally I'd go for a bit of trouble and get a more eyepleasing result. :)
     
  5. DrCraze
    Joined: Apr 2010
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    DrCraze Junior Member

    I am currently building a 17 foot pacific proa out of ferro-cement. I am building it upside down using a male mold. The mold is made from a weak adobe mix so if I have trouble releasing the mold I can simply dig it out. However I will be covering the mold with several layers of thin plastic sheeting before the layup.
    Ill be using some products from the concrete countertop industry and making the hull thickness 1/4inch.

    I think your build is very doable but the plaster day sounds monumental. I would design a modular pontoon design and keep the sections small enough for a few workers. The advantages wouldn't stop there. You would need any heavy transport and I,m no engineer but I believe you could keep the hull thickness down to 3/4" to 1" thick.
     
  6. tugboat

    tugboat Previous Member

    Lurvio- i loved your design--i had one drawn up very similar...and the hull form is a bit more effective in a chop, the only diff is youll lose some deck space and its probably even as easy to build.
    about the hull thickness- I agree to a point-- one inch thickness is used on boats to around 60 ft. (check the navy ferro-cement guide) the u.s. navy used 1 inch thick on the 65 ft patrol boats. at 100 ft you could get away with around 1. 25- 1.5 inches easily. that might mean an extra layer or two of mesh. One thing that should be mentioned is- the bigger you build a boat in FC- the more cost savings your going to get in comparison to other materials..steel for a 100 ft hull is going to bankrupt the common man. 100 ft with a big beam is only really viable in FC. the advantage is the monocoque contruction making he whole boat one unit. very stiff...less hogging and sagging wracking strain, etc. the metal won't fatigue and the cement continues to cure harder forever.

    Hi Rummy- - gunite - has not been used vbery much --i hear it creates a lot of voids,..and i wouldnt recommend it,..but thren again what do i know...since i havent used it..i cannot say one way or another....
    -the ferro psi is supposed to be around 19 000 to 21 000 psi impact resistance. (again look at hartley and brookes tables for that info).
    this is because of the reinforcement of the steel rods , the built up layers of mesh, and the sand in the concrete being very fine with,i believe, a 1:1 ratio...beach sand type. this givse the concrete a very high Mpa. this is the keys to a solid and strong hull,

    DrCRaze- oh yes! on pastering day you for a 100 ft hull you would need many people - but you could do it in the "two shot method" meaning you can plaster just the outside of the hull..let it cure over nigvht and do the inner hull at your own leasurely pace. this is now the standard method for fc.

    I wanted a submarien so bad..i had designed it out of FC i had all the systems worked out...at this moment i could start the build -i have the engine and components needed..but i think i may go with a navy/army st tug 45 ft but built out of ferro cement. i have a great diesel to throw in that.
    i have the plans for that complete with offsets! cant wait. hope to start setting up the strongback for it in july and cut the frames out about thwat time.

    one other thing i should mention--there are more than a couple ways to build in FC..you can can build right side up--or upside down. you can use open molds or closed- you can use a truss method or a pipe method...there are pros and cons for each...in the barge case--id go for a truss method and simply lay the trusses on a strongback levelled properly.
     
  7. tugboat

    tugboat Previous Member

    DrCraze--id love to see some pics of that when done..i thought about that too--i did some experiments using sono-tubes for forms. 1/4 inch though will still be heavy...how did you over come the weight issues?..it would make a great cruising hull. not a racer...

    oh yeah! almost forgot one other thing friends...if you do build a barge --build lots of curves into it..i.e. radius the chines and the deck needs to have a slight camber- shapes with flat planes need to be reinforced with webbing . so the best barge hull would be a radius or round bilge type.
     
  8. Lurvio
    Joined: Jul 2009
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    Lurvio Mad scientist

    Tug
    OK that is really interesting. Obviously 1'' thick hull won't be build in typical concrete used in buildings. :) My sketch is for that basic concrete you can order by truckload. And it wouldn't be for efficience, it's basically a floating rock. LT stated he didn't have to sail that much/fast so the heaviness IMO is a good thing. It'll make a real steady platform for a liveaboard.
     
  9. tugboat

    tugboat Previous Member

    Lurvio-- yes there is a big difference in standard concrete and ferro-cement...If the dock is not going to be moved often(barge in this case)...then perhaps a thicker wall is desirable since you can built square shpes easier...how thick were you thinking?...it would be pretty heavy at around 3 inches of concrete... i believe you would still have tyo use a lot of steel to reinforce the whole enchilada- so the costs savings on ferro- may be more..i dont know...

    in case you have never seen how ferro is laid up-- you would build a armiture- this could be a mold out of ply wood or strip plank or it could be actualy steel frames made from black pipe or from a truss type of frame. then the hull is strung horizontally with 1/4 inch mild steel or high tensile steel stringers(if available), then same thing done vertically so you have a webbing. this is tighhtly spaced about 3 inches apart for both...then the whole thing gets an inner and outer layer of(depending on what you prefer) either 1/2 inch chicken wire or 1/2 inch mesh. ideally you would use 8- 10 layers in all. the more layers..the thicker and stronger the hull. there is an optimum number of layers too many will be too costly and be hard to work through with sand/morter mix. this creates and unbeleivably rigid and strong monocoque structure....when done right it will have 19 000 to 21 000 psi in impact resistance..and nearly as high compressive strength. which is why i advocate its use for a submarine. its the ultimate boatbuilding material- will not rot-decay--extrememly durable- is imprenetrable by borers, fire proof, needs zero maintenance and barnacles are easily removed. needs literally no maintenance. but its heavy.
     
  10. Lurvio
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    Lurvio Mad scientist

    Tug
    Thanks for the explanation. :) Live and learn.

    I did a quick guestimate on the weight of my sketch, 140 metric tons. The hull would have about 1 meter of draft, so half the hull height. The hull thicknesses were stated in the posting of the sketch, 12'' bottom, 10'' sides etc.

    Lurvio
     
    Last edited: Apr 16, 2010
  11. Rummy
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    Rummy Junior Member

    pontoon hulls

    Just wondering where the lake was. Also, can you get an old barge for a hull. Or why not get a couple of prefab pontoon or cat hulls in FG or Alu. It seems like you could even place them end to end and the maneuverability would be adequate for your needs.Two side by side and two end to end. There's plenty of manufacturers in the states and OZ that make these and they are containerable. Just seems like an 80' concrete hull in one pour is unobtainable. Regardless Good luck
     
  12. capt littlelegs
    Joined: Apr 2010
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    capt littlelegs New Member

    I've got a 1980's 35' WL x 12'6" beam Jay Benford design ferro motorsailor built in Lloyds approved materials by a professional boatyard, she's quite solid and heavy at 13 tonnes and impervious to everything but a sea mine! Might be worth contacting Lloyds for recommended material requirements if you go this route.

    I've also got a 1920 86' x 16' Dutch Luxemotor steel barge less than 50 tonnes unladen and capable of carrying 80 tonnes.

    I'm no boat designer but considering your use and the weight penalty and huge one hit plastering problems of ferro of that size, I seriously think you'd be better off in all ways with a lightweight steel or alu hard chine design possibly prefabricated plate or sections as suggested. Something like that could always be built off site and easily transported in sections.
     
  13. Rummy
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    Rummy Junior Member

    Ain't no way

    I'm a life long builder and have poured 10s of thousands of yards of concrete so I know a little about it. Doing some rough calcs from Lurvio's post and I come up with about 82 yards of concrete for the vessel. In the states concrete trucks are between 7 and 10 yard capacity. So thats 12 large trucks or 8 extra large trucks. To put it another way visualize pouring a slab that measures 80' by 80' in one day in one pour. We refer to our concrete mixes as a 5 sack or 6 sack design. That's one 90 lb bag of cement per yard. So for a relatively weak (for boat building) 6 sack design mix you would need about 492 bags of cement which weighs 44,000 lbs. Who's going to lift 44,000 lbs to put it in the mixer one bag at a time in one day? And judging by the high PSI numbers you would probably have to multiply that considerably. With a hand mixer and inexperienced help you'd be lucky to be done in a week. Just...Ain't no way. Ferro cement is not the way to go for this one. I won't help but I will buy the beer.
     
  14. Lurvio
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    Lurvio Mad scientist

    Rummy
    I got about 70 cubic meters of concrete, roughly 2 tons(metric)/m3. Should be in the same ball park as your 82 cubic yards.

    - - -

    My woodwork shop is 23,1 x 8 meters and we did the 10-12 cm floor slab in five segments and five days, 18 m3 of concrete. We had a 800 liter tractor mounted mixer and sand/gravel was loaded by another tractor. It was still a big effort for three guys.

    I quoted (fall 2007) the concrete from a local supplier, it would have been about 110 euros/m3 delivered (30 km distance), the cement and sand/gravel cost less than half that.

    For the hull pour (this size) buying makes a lot more sense, hand mixed concrete always has variations in composition, which isn't a good thing in a boat. Trucks here in Finland carry about 10 m3, so seven loads. 1100€/load makes 7700 euros for the 80ft hull. And as Rummy said, mixing 70 cubic meters of concrete aint gonna be a picnic. With a rented big *** mixer and right machinery, maybe.

    Lurvio
     

  15. tugboat

    tugboat Previous Member

    Rummy--(and with all due respect to Lurvio's design)- you dont need that thick of walls for ferro cement--1.5 inches is plenty! for an 80-100 ft'r--it wouldn't need 6 ft or 2 meter sides...
    for rivers it would be very seaworthy at about 3ft sides. so assuming maybe
    using a slightly less beamy barge design say 16 ft beam...i calculated the total for ferro cement at 1.5 inch hull thickness- about 24 cubic meters...thats an easy pour. you have 10 or 12 guys doing the outside only, at 1.5 inches thickness...you could easily make that hull in ferrocement--doing it in standard construction would be harder and more costly and of course more time consuming, with thicker walls unecessarily using up precious freeboard.. for me ideal dimensions for this would be 80 ft long- 16 ft wide- 2 ft freeboard or 3 ft depth - and 1.25-1.5 inch thick walls-
    built with a truss type frame--using a flat slab as the total sq ft.

    added up i get 32' width (16'x2-bottom and topside) x 160 loa,

    32ft width x 160 length = 5120 square ft + sides + bow+ transom= 5120+(3ft x 2 x 160 loa)+(3 x 2 x 32 beam)= 5120 + 1152sq ft= 6272 ft sq (also note that number is also more than a nautical mile in linear feet). add another factor of 10% for extras i.e. webbings etc...
    6272 x 1.1 = 6688 total square ft roughly---24 cubic meters (if box shaped).... add the margin +- 10% = say to be very generous 24 cu m (aprox) x 1.1=26.4 cubic meters.

    thats much less than the over 70 cubic meters calculated! to be exact its 24/70 x 100 or roughly 65% less!! using 12 guys NO problemo!

    of course, if he is going to build it , im gonna buy chicken wire stocks cuz i expect the stock prices of chicken wire to rise on the decreased availability of netting because of this project!!

    but its doable rummy- get that beer ready!!(lemonade for me -beer yuck!)

    and a freindly reminder --the U.S navy and other countries created many 5000 ton displacement vessels out of rebar and concrete..300 ft'ers! but they were built too heavy.. lasted many many years -some are still around as breakwaters- ala, the powell river b.c. check out the website. some are still floating.

    one more quick note--building in floats i.e. pontoons--same or more surface area..so the barge is better.
     
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