We love Ferro cement but beware !

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

  1. rwatson
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    rwatson Senior Member

    Have to disagree there, Tuggy old mate.

    Fibreglass is at least 5 -7 times stonger than steel pound for pound, let alone concrete. Look at the great increase in strength when you add .... fibres .... to concrete.

    Say the concrete boat hull is ... u dunno, 2 inches thick, a two inch thick fibreglass hull is waaaaay stronger in all respects. Now if a concrete boat weighs say 5 tonne, 5 tonne of fibre and resin will be much, much stronger.

    Its true, the average yacht with a fibreglass hull of say 1 centimetre will never be as strong as a 3 centimetre concrete hull - but we are not comparing "apples with apples", as the saying goes.

    This is ignoring the cost ratio of course, where concrete shows its "strength". Lets face it, cost is the only reason anyone would consider concrete over fibreglass, both from a strength, build time and maintenance point of view.
     
  2. LyndonJ
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    LyndonJ Senior Member

    The downsides to FRP is that polyester resin really has a finite life, and its not very stiff so it needs more shape holding framing as the boat gets large.
     
  3. tugboat

    tugboat Previous Member

    @lyndonj- First--I was agreeing with you as far as steel being a superior material for a commercial boat or even a cruiser. and as for boats vs Ships- to me it doesnt seem there should be a diff...in fact commercial vessels are more heavily built with double bottoms and extra transverse framing etc. and as such should be stronger. yet they get holed and if there are collisions they do get ripped apart! common sense is all that is needed with that argument - but as they say-common sense- aint so common...
    anyway have i been on board when a vessel split up?--no i personally haven't seen that or you'd be talking to a ghost since when a steel hull on a "SHIP"- fatigues and splits apart i doubt id be alive to tell the story-- and its happened many times on the great lakes.

    ice bergs split up steel boats all the time if you hit them--the edmund fitgerald for one- and um perhaps you remember the titanic? ruptured hull!? a huge gash across quite a few bulkheads??!..there are many others...
    but --dont believe me..

    but like i said if i was going to build a commercial boat or a character tug- it would be steel...so what are we disagreeing about again?
    my point is ferro- is a viable alternative.

    this is what happens to a steel vessel when it hits an immoveable object:

    http://www.youtube.com/watch?v=sTVbO8zq7Tc

    tell me now this didnt rip open...
     
  4. tugboat

    tugboat Previous Member

    rwatson- yes i agree cost is a big factor but so is strength...cored hulls would not be stronger than a laminate layup perhaps-

    lighter yes but not stronger.
    now take that to the next level- take a core of concrete- epoxy and glass both side of the concrete and you would have a very strong hull indeed!! then you have a concrete composite hull...
     
  5. tugboat

    tugboat Previous Member

  6. LyndonJ
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    LyndonJ Senior Member

    Tug

    Repeat ad nauseaum

    They are ships not boats. The point is that boat size vessels made of steel don't rip open and fall apart or split in the middle. Boat sized vessels made of steel have such strong and stiff plating relative to their size that they tend to take groundings in one piece without holes but with dents.

    FC matrix is very brittle and weak in shear and tension, that makes the materials damage response abysmal relative to steel at acceptable weights.
     
  7. rwatson
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    rwatson Senior Member

    Weeeelll .... polyester resin has a finite life before cure, true but so does concrete (it all tends to go hard despite valiant attempts to keep it dry)

    I presume you mean stiff as in fibres while placing the mould ( the cloth sags all over the place). You could use C-Flex, which is like steel mesh to lay out, then you dont need large amounts of moulding or framing.

    Not very important problems in my mind.
     
  8. LyndonJ
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    LyndonJ Senior Member

    There's planty of holes that sunk ferro boats posted.

    You go and find some that sunk steel boats. Say between 30 and 60 feet long.

    You'll find lots of deted scraped creased hulls but surprisingly intact and watertight.
     

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  9. tugboat

    tugboat Previous Member

    LyondonJ- with all due respect-I am not going to change my mind that ferro cement is an excellenmt alternative to steel or fiberglass..im not alone in my thinking either--how about--ill build my boat how i want- and you build yours how you want?...i prefer steel...for the types of boats i like

    Rwatson- actually i have seen commercial vessels on the west coast here -tugboats-built in fiberglass--but man! that must have been expensive to build and if it cracked-- more difficult to mend than steel, maybe the same as ferro in the ***-ache dept.
     
  10. tugboat

    tugboat Previous Member

    LyndonJ for shame!!-- are you suggesting that steel boats cannot sink or that none have from a holing in that size range?...
     
  11. LyndonJ
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    LyndonJ Senior Member

    Significant factors with polyester.
    Crack propogation, which gets worse with matrix aging, the other real bugbear is hydrolysis. The material gets broken down by water which it absorbes with a vengence made even worse as the material micro cracks.

    The crack propogaton is interesting and if you look at the engineering properties it cracks easily on a micro scale and the crack runs until it hits a fibre. This happens under normal cyclic design loads. Similar to fatigue I suppose.
    This is why FRP loses stiffness with age. Although I'm talking decades of use it is not as long lived as a good FC hull for example.
     
  12. LyndonJ
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    LyndonJ Senior Member

    This was the subject I came in on, where are you ? It sounds like a very emotive and unsustainagle beat up on steel, so you could choose FC that's all.

    And again where is that thread "The steel designer of tugs" ????
     
  13. rwatson
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    rwatson Senior Member

     
  14. capt littlelegs
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    capt littlelegs New Member

    I also own a ferro boat of 38' OA and I'm very pleased with it and don't have to worry about it getting wet in or out, nothing happens, no rust, no osmosis and no rot. It was professionaly built with Lloyds approved materials to a Jay Benson design who also recommends the best materials, no chicken wire in it! Properly build and designed with no dangly bits there is nothing to break off and if it did sustain any collision damage they are easy to repair. You'd be amazed how strong it is and many people think it is fibreglass. I have seen naval vessels built in fibreglass and lifeboat rescue vessels of about 50' but they are very expensive to be that tough!
     

  15. rwatson
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    rwatson Senior Member

    Yes, expense is the big factor. Note that osmosis and other problems occur with PolyEster resin, but if VinylEster and or Epoxy is used correctly, most of the fibreglass longevity problems go away. This should make a fibreglass hull on par with the low maintenance of ferro.

    The other big factor that has been pointed out so many times is that the hull cost is a very small percentage of the overall boat cost.

    So, if you save 50% on hull cost, you are only saving, say, 10-15% of the total cost of the boat.

    This brings in the fact that non commercial boats are owned for less than 10 years by 80% of owners, (health, family, relocation, maintenance costs) and generally speaking incur a resale loss.

    I have no figures to prove it, but years of gazing through boat sale ads seem to show that ferro hulls are much harder to sell, and incur bigger depreciation than other materials - I guess due to stories about badly built hulls.

    The real discussion may be less about "better" materials, but more about lower cost for the same life cycle and usage of a given boat type.
     
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