Ferro-Cement Multihull Scantlings

Discussion in 'Multihulls' started by DrCraze, May 19, 2010.

  1. tugboat

    tugboat Previous Member

    Dr craze-- whats the status on your project???..im very interested ..have you sailed it yet?
     
  2. tugboat

    tugboat Previous Member

    i did think of using 18 guage steel for a tri or cat--lighter than ferro and very ductile...and it could be made monolithic by using variations of the origami method...like a steel stitch and glue tri...could run reefs...
     
  3. ThomD
    Joined: Mar 2009
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    ThomD Senior Member

    "If it didn't then there wouldn't be concrete canoe competitions for civil engineers every year."

    I'm actually curious about all this, but there may be a reason it is CEs designing these canoes.
     
  4. Samnz
    Joined: Nov 2008
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    Samnz Senior Member

    My parents built (in the 1870s) and still own their 45ft cruising yacht built of ferro, its lighter and faster than the original timber design or the mass produced fibreglass boats of the same design and has done over 10000 ocean miles somewhere you've got your facts well and truly mixed up.

    by the way im not a believer im building a composite 8.5m tri, but your plainly wrong, a badly built ferro boat is ****, just like any badly built boat is **** including alloy, composite or timber etc

    the only reason so many ferro boats were badly built is because they were viewed as a cheap easy home build material and novices got it wrong in many cases
     
  5. Samnz
    Joined: Nov 2008
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    Samnz Senior Member

    read the gougeons book on boat construction its brilliant.
     
  6. ThomD
    Joined: Mar 2009
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    ThomD Senior Member

    They came up with a protocol for using something called a hydromat. This was picked up as an official test by SNAME, and SNAME presumably has other tests.

    Such testing might have been out of reach in the old days, but the internet, ebay,craigs, make all kinds of oddball stuff affordable these days.
     
  7. DrCraze
    Joined: Apr 2010
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    DrCraze Junior Member

    Land Shark rolls
    [​IMG]

    Floats
    [​IMG]

    And sails!
    [​IMG]

    The last photo shows the proa with two passengers. Total payload is about 390 lbs. I jury rigged a windsurf sail for the day but I should have the intended sail finished soon.
     
    1 person likes this.
  8. CT 249
    Joined: Dec 2004
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    CT 249 Senior Member

    How do you achieve the very flat leach (one of the most striking characteristics of a modern windsurfer sail) with a crab claw sail?

    One of the fascinating things about windsurfer sails is that it's so easy to take a rig from one type of board and change it to another style of board in a few seconds. That really underlines the fact that a windsurfer rig can be very slow in the wrong conditions, or when pushing the wrong hull.
     
  9. DGreenwood
    Joined: Aug 2004
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    DGreenwood Senior Member

    A "true believer" proselytizing his convictions shall not be swayed by mere facts!
     
  10. Steve W
    Joined: Jul 2004
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    Location: Duluth, Minnesota

    Steve W Senior Member

    The guy is not proselytizing, nor is he looking for us to proselytze to him, he is asking for info on material testing, anyone able to answer his question ?
    DrCraze, your boat looks to float just fine, congrats. Did you happen to weigh the main hull by chance?
    Samnz, what is the design of your parents boat? you said it was originally designed for wood construction.
    Steve.
     
  11. Steve W
    Joined: Jul 2004
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    Location: Duluth, Minnesota

    Steve W Senior Member

    DrCraze, back in the 70s a company in New Zealand,i think it was Ferrocraft Marine ltd built a few 40ft flush decked Laurie Davidson designed modern fin keel sailboats which were cored with treated radiata pine in place of the longitudinal steel,i wont pretend to know the details but they were a very hansome modern yacht at that time and indistinguishable from any other material, some of them went to New Caledonia, i saw one for sail a few years ago in BC. I have no idea if it was a sucessful method or not.
    Perhaps Samnz may know something of these boats?
    Steve.
     
  12. dstgean
    Joined: Aug 2006
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    Location: Chicago Area

    dstgean Senior Member

    sailing proa

    Dr Craze,

    Interesting and fun! Lots of flack out there, but beating the weight of a dugout is possible and probably easy. I'm sure you'll have fun with it either way.

    Dan
     
  13. Samnz
    Joined: Nov 2008
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    Location: Auckland

    Samnz Senior Member

    Herrishoff Mobjack funny thing is they joke about the only part of it which needs zero maintenance and doesnt leak is the hull. The teak teaks are a nightmare...
     

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  14. DrCraze
    Joined: Apr 2010
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    DrCraze Junior Member

    I think I used a little over 400 lbs of cement plaster on the main hull. Given that 10 to 15 percent of every batch ended up in the dirt I would estimate the displacement to be around 350lbs for the main hull alone and about 100lbs for the ama.
    This build was intended as an experiment and it turned out to be very enlightening. I'm now having dreams of an 80' proa with a tiki bar:p
     

  15. rberrey
    Joined: Oct 2010
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    Location: AL gulf coast

    rberrey Senior Member

    Ask your concrete supplyer to loan you their beam molds , they should have a few and if not thay can tell you where you can get some. Pour some cylinders as well , take them to a concrete testing lab and get them to break them. The beams will give you the flex , the cylinders the compression. I dont know any thing about ferro cement, I would think it is a light weight concrete, if you are not using ferro as I see the word plaster I might would rethink my mix.You have added kevlar in why not add fibermesh as well then epoxy the hull in and out. Also if you can get products from Grace why not add some other products, put your mix to sleep, this adds strength and allows you to plaster the whole hull with one mix batch. A little xypec in the mix will help water proof it. Composite rebar or bamboo would would lighten it as well and wont rust. I would get someone to do a mix design if
    i were going to build a 80' hull. rick
     
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