examples of (classed) yachts using bladder tanks

Discussion in 'Boat Design' started by expedition, Oct 16, 2009.

  1. expedition
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    expedition Thorwald Westmaas

    We plan to use bladder tanks to store jet fuel. We have a rather compact area available and in order to create the required coffferdam space and make it inspectable, bladder tanks are the solutin.

    I was told by a L/R surveyor that it's not uncommon to use bladder fuel tanks, especially on GRP.

    One of the main concerns for L/R is that the tank maintains its shape regardless of how full it is so the connections to the tank can be fixed (versus some kind of flexible hose configuration.

    I've already been told about materials that can be used to accomplish this and can be removed (remember, the bladder tank must be removed to inspect the surrounding cofferdam space) but I wonder if anybody here knows of yachts using bladder tanks which can eventually lead me to some manufacturers that have experience with this kind of (custom) setups.

    Thorwald
     
  2. apex1

    apex1 Guest

    There have been several systems around in the 80ies (Vetus sold one too) but I could´nt find one left when I searched one year ago.
    I would like to have such system too (and the cofferdam), but had no success by so far.
    Partially filling is the problem with all the systems I found.

    Let me know when you find one.

    Regards
    Richard
     
  3. wardd
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    wardd Senior Member

    perhaps rubber boat makers?
     
  4. expedition
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    expedition Thorwald Westmaas

    Hi Ward, Richard,

    It's not so much the tank material. There are plenty of bladder fuel tank fuel manufacturers but none list any specific expertise with ships and none is certified by any class society.

    That's OK. They will simply have to be tested against leaks which is not a problem. The issue is keeping the tank from collapsing when it's empty.

    I've been pointed to these people and this application - http://www.crestfoam.com/news14.html - and am waiting for their reply.

    The material is called: "Explosion Suppressant Foam" and if you Google it, you find more websites like this one here http://www.customfoams.co.uk/cf/content/products/esf.htm although they are using the material produced by Crestfoam.

    Seems like something that could work.

    Thorwald
     
  5. apex1

    apex1 Guest

    Hi Thorwald,
    I´m completely confused now. Collapsing is what the tank has to do! (Not the cofferdam, I hope). That is the only advantage I can see, no need for baffles in a conventional metal built space (tank). Just one or two "liners" inside the tank and tere is no free surface to cope with.
    The foam stuff would make it impossible to inspect the tank space inside!?
     
  6. wardd
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    wardd Senior Member

    in aircraft the bladders are laced to the structure to keep their shape

    unlaced to remove
     
  7. expedition
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    expedition Thorwald Westmaas

    No Richard,

    L/R does NOT want the tanks to collapse when emptied because they don't like the concept of flexible hoses to connect the ventilation and fuel filling piping.

    So using this foam material we should make pieces that can be located inside the tank to keep it up while still be removable. Basically combination of colums and beams made from foam, held in place by some place holders made from the same bladder tank material.
     
  8. apex1

    apex1 Guest

    Yes, yes, I know that is the prob! They do´nt like all the wishy washy stuff. And for some understandable reason, that did wear out soon and unpredictable.
    But now I´ve got the idea with the foam, sounds possible. But cost? We are talking quite several m³ in both of our vessels.

    Btw. where did you end with your cost calculations? I assume we both came to the same result?

    Richard
     
  9. expedition
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    expedition Thorwald Westmaas

    Well, we're talking about 3 m3 per tank so it's not like huge. Of course, I have no clue yet how expensive this material is but we probably don't have to fill the tank completely.

    Say a flat 'ceiling' part supported by 6 40x40 cm 'columns' might do the trick but that's something we'll have to calculate.

    At any case, an interesting "problem" to solve.

    Thorwald
     
  10. apex1

    apex1 Guest

    Hmm, I thought maybe it would do, having the foam just covering the baffle cutouts (large ones like manholes). And I plan to have some 16m³ tank in a cofferdam.
     
  11. wardd
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    wardd Senior Member

    they solved the problem in aircraft decades ago
     
  12. apex1

    apex1 Guest

    No they did´nt! Have you ever seen a aircraft tank serviced? Did you notice the size of the gnome doing it?
     
  13. wardd
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    wardd Senior Member

    yes and i have done it
    i would refer you to the ch-47 fuel nacelles as one example of an attached bladder
     
  14. apex1

    apex1 Guest

    Whats that wardd?
    It would be really a great help to find a proven solution.
     

  15. baeckmo
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    baeckmo Hydrodynamics

    Excellent example of a brain saltomortale! Ever emptied a box of wine, gentlemen? The collapsible bladder tank does NOT use any venting! The vent is to the cofferdam volume, and the filling/emptying of the bladder is via a fixed bottom manifold.

    The problem of sloshing is still there, unless you use multiple bags, each in its own stiffened cell, and connected to the bottom manifold.
     
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