We love Ferro cement but beware !

Discussion in 'Boat Design' started by manta.bay, Feb 23, 2008.

  1. dskira

    dskira Previous Member

    Do you still have pictures.
    I love tramp steamer
  2. dskira

    dskira Previous Member

    During the emergency float in WWI the ship designed by Ferry were built of steel wood and ferrocement.
    They abandoned the ferrocement as to expensive, they built 250 wooden vessel and same in steel. The war ended before they needed these vessel.
    Some still running.
  3. tugboat

    tugboat Previous Member

    Good topic Gonzo- I have wondered about using that too--i called a couple places here and talked to some engineers. it is like 15 bucks extra for the fibers per cubic meter. and i believe they add immense strength. they are being used a lot now in modern construction of concrete structures...i personally have never used it but probably will when the time comes...

  4. tugboat

    tugboat Previous Member

    Masalai- true- i have a samson book and there are accounts in it with a trawler that hit a reef and took out the reef and not the hull! and a guy with a 50 ft ketch that hit an iceberg and it wasnt until he got back to port some weeks later that he noticed a gash 8 inches- but it didn't harm the boat in the least!!
  5. tugboat

    tugboat Previous Member

    Sorry Bruce46 I disagree on that one--i just did a cost check on both materials using welded mesh(which in my opinion is better and also more expensive)
    the ferro hull- was about 1/2 the cost. and almost the same strength and you don't need a building platen.
    steel for the boat in question not including the forming costs for a round bilge and the framing- having the metal nested and cut by water jet or cnc if big enough, totals 3 times for what a ferro hull costs...the plate costs without the weldment alone is the cost of a completed ferro hull.
  6. tugboat

    tugboat Previous Member

    lets see steel survive what this vessel went through- page 72 of pdf document shows pics! http://www.boatdesign.net/ferro/ferro-2.pdf

    An unattended fishing vessel is driven onto
    remote Bahamian reefs in a storm. Before finally
    wedging herself on the reef the vessel, her anchor
    chain parted, pounded her rudder shoe severely
    on the rocks. She lay for two weeks on the reef.
    Later it was found that the propeller shaft, due
    to the ferro-cement deadwood having been
    poured solid with concrete, was as true as the
    day installed. Photos reveal the damage.
    The reef-bound vessel from the air.
    Damaged steel keel. Minimal damage to ferrocement
    Rudder shaft
  7. tugboat

    tugboat Previous Member

    Mike -ill hunt around and find some steel pics of punctured hulls and ones that have died on reefs. Btw -i have talked to a steel designer of tugs on one of my threads...you guys should read it and what he says about steel and how easily it gets punctured...fg shatters, wood holes, steel rusts out, and shears punctures...so it doesn't matter the material all materials have limits..
    1 person likes this.
  8. LyndonJ
    Joined: May 2008
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    Location: Australia

    LyndonJ Senior Member

    Could you give us a link to those posts please.

    You can use anecdotes all day and never learn anytthing useful. The material properties are everything in structures, strength and stiffness. Those get compromised for weight and corrosion resistance.

    There's simply no way you can beat steel as a structural material, it is the strongest stiffest and most easily joined material.

    I think the point of the ferro damage pics posted was to illustrate the brittle failure modes of the matrix. Note that the steel had not even deformed in the cracked rudder base picture but the brittle matrix had crumbled.

    The classic shear puncture of the hull shows a collision off the rebar and in the mesh section since the damage is so localised. This would be the weakest area.

    If you specifically want something to survive collisions abrasion and reefs then steel is your material.

    Heres' an anecdote too: Was it Airlie beach last year the cyclone piled a few boats up on the rocks, the big ferro sailboat ended up between a steel boat and the rocks and was ground to a pulp while the steel boat was still floating even though after it had finished with the ferro boat it was on the rocks too.
  9. Pierre R
    Joined: May 2007
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    Location: ohio, USA

    Pierre R Senior Member

    If you want to increase the impact resistance of cement the best option is the addition of cement grade fume silica. A second best would be burnt rice hulls. A distant third is fly ash.

    Adding these in conjunction with polyester fiber would be great except for the fact that cement with fiber does not trowel or screed worth beans.

    There is a product called Permacrete that trowels unbelievably good and is much stronger than normal concrete but Permacrete is probably prohibitively expensive.
  10. DrCraze
    Joined: Apr 2010
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    Location: North America

    DrCraze Junior Member

    Its funny you say that Pierre. I happened to have just finished a ferro hull yesterday. I added a max dosage of fiber and had zero issues with it. I would say water reducer and super plasticizers are the most important thing to add to your mix. Pozzolans are a must too, A product called "Power Pozz" is what I use.

    All this stuff does nothing if you dont know how to work it. Work it to long and you get a weak finished panel due to breaking the cement hydrate bonds after they have made there initial set. To little and you get a rough surface that can sometimes evaporate water too fast causing curing problems.
  11. tugboat

    tugboat Previous Member

    DrCraze- congratulations!! I am very interested in knowing what type of vessel and how big?...did you use mesh or chicken wire?
    If you have any pics--i would love to see them...?
  12. tugboat

    tugboat Previous Member

    Lyndonj- actually i am in agreement with you on one thing and that is steel- is probably the strongest material you can build a Boat with--subs may be different since you can make 6 inch thick hulls if you want- but for a workboat and everyday use that takes a beating- because of steels characteristics, i agree-it is the best material to use for a work boat or maybe a cruising hull---btw have you read any bernard moitessier?- he states that his joshua would have been better built using light light guage even 1/16th of an inch for his boat as he said his cruiser was overbuilt.

    as far as materials it also depends IMHO on how well the boat was built. a good ferro boat is still better than poorly built steel one.
    having said that ferro- is stronger than fiberglass or wood.

    I still have seen steel boats easily ripped open- talked to designers who call for 1/2 inch plate bottoms, and just google the skeleton coast or look at any big reef and you will see steel hulks lying there ruined rusting away- those are the facts. steel is not impervious to destruction it requires high maintenance, there are advantages and disadvantages to all materials...
    objectively i had worried about building in ferro because of the crumble effect. but again there are ways to stop that as was just posted in the last couple posts about ways to beef up the brittle nature of concrete.

    I think its all a personal choice on what material. i wish steel wasnt so damned expensive..contrary to popular belief, the hull of a tugboat is more like 2/3rds the cost of the build -if you use -used engine-parts etc. since your going to have a wheelhouse-wheel - prop shaft-rudder-a couple of controls etc etc..it is very bare so its not a yacht. hence the costs are the hull and engine mostly. fc is still viable as a second choice for strength. and will outlast a steel vessel if done right...and cheaper to maintain and build.
    for a tugboat i do still prefer steel.
  13. DrCraze
    Joined: Apr 2010
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    Location: North America

    DrCraze Junior Member

    Its 17.5ft 240lbs of proa madness! I posted a pic in my Proa-Cement thread. All up it will probably be around 400-500 lbs. By visual reference it should have a 12 inch draft. The hull thickness is 6mm. I used chicken mesh to keep the cost down but I added lots of spooled 19 gauge wire to my layup for stiffness since the hexagon mesh tends to flex more than welded 1/2 inch mesh.

    This build has definitely shut a few trolls up for sure:D
  14. tugboat

    tugboat Previous Member

    wow- i experimented with this about two years ago- using a single layer of plasterers lath and a sonotube for a form. i shaped the bow by cutting darts from the sonotube. i used a special high strength concrete that is made with a special magnesium sulphate additive.- i.e. you dont add water, you use a bottle of green liquid that comes with it for the reaction.
    the stuff was called MG Krete- and hardens to 11 000 psi. what i didnt know at the time was that regular concrete would have worked. this stuff is a quick drying topcoat. at 60 dollars for a 40 lb bag it would have been expensive. so i dropped the experiement. the result was at 1/4 inch a very heavy hull.I treid to go 1/8th inch but it was too thin and brittle. I estimated my total hull to be around 600-700 lbs at 1/4 inch....i never believed what the designers said about mulithulls not being possible in ferro. If you build a good size vaka and amas in it--it should work. a great reef runner!! your boat should probably be fast as about the same weight as FG.

    great job!!

  15. LyndonJ
    Joined: May 2008
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    Location: Australia

    LyndonJ Senior Member

    I'm sorry but I really doubt that youve seen steel boats 'ripped open' as you put it punctured maybe. I'll beleive it if you could point to photo's and cases that would illustrate the point. Otherwise I think you have just absorbed someone elses dodgy opinion. Also differentiate between ships and boats there's an important distinction.

    I asked for a link to the thread you said illustrated this, where is that thread ? I really doubt any NA or Eng worth his salt would take that line.

    As for wrecks on reefs. The wrecks are there becasue old, poorly manned and poorly maintained fishing boats run onto reefs. Salvage is neither affordable nor available. To use this as a materials argument is not logical.

    If you listen to all sorts of misinformation you come out with more mis-information.

    There are many 100 year old steel vessels around that were well maintained and still operational, mainly private yachts since thay don't suffer from the commercial economic life cycle decisions that determine commercial vessel life.
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