What do you call the liquid that remains in a ship's tanks when they are emptied?

Discussion in 'Boat Design' started by philSweet, Feb 23, 2020.

  1. philSweet
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    philSweet Senior Member

    On land, and on highways and railways, what remains in an "empty" tank is called the heel. But it occurs to me that this would be a really awkward term to use on ships. Is there an alternate term used in shipping?
     
  2. BlueBell
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    BlueBell Ahhhhh...

    Swill.

    Unclaimed.

    Unaccessible reserve.

    I don't know.
     
  3. JSL
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    JSL Senior Member

    Sludge???
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    That is what I call the sediment "mud" in water tanks.
     
  5. KJL38
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    KJL38 Junior Member

    I just asked my wife who is a marine quantity surveyor and she said there shouldn't be anything left but it would be called "remaining on board" (ROB).
     
  6. jehardiman
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    jehardiman Senior Member

    fallguy and Ad Hoc like this.
  7. Ad Hoc
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    Ad Hoc Naval Architect

    JEH nailed it
     
  8. Cacciatore
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    Cacciatore Junior Member

    Sludge is the bottom sediment of a fuel tank for example Heavy Fuel .Generally for the ballast tank is used sediment or mud . Ullage and Sounding are method for check the quantity of a liquid in a tank using the sounding table and a sounding tape. If the sounding tape have a floating initial part you misure the ullage of the tank if is sinkable you are performing the sounding.
     
  9. Tiny Turnip
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    Tiny Turnip Senior Member

    The measurement from the surface of the liquid in the tank to the bottom of the tank (the remaining liquid) is the sounding. the measurement of the space above the surface of the liquid to the top of the tank (the used or lost liquid, or angels share in whisky barrels) is the ullage. Strictly speaking I believe the terms refer to the measurement rather than the actual liquid.

    Is 'dregs' any use?

    Understanding Sounding, Ullage, and Frequency of Sounding https://www.marineinsight.com/guidelines/understanding-sounding-ullage-and-frequency-of-sounding/amp/

    Ullage http://shipinspection.eu/ullage/
     
  10. jehardiman
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    jehardiman Senior Member

    Yeah, ullage is one of those snarky terms we naval architects deal with all the time that has various meanings depending on context. Literally, ullage is the empty space in a liquid container. In shipbuilding, a tank only has one "capacity", and that is the total volume until the fluid begins to enter/exit the vents. So what do we call the amount of fluid in the tank when the tank is not at full capacity? The "ullage" of a tank is the general term.
    Realistically, you could sound (measure the depth of the fluid in) the tank or you could measure the head space (the ullage measurement) in the tank. Note that a sounding tube does not have to be vertical, but the ullage measurement generally is (but not anymore with ultrasonic/RF ullage/capacity gages) . In any case, there is a table/graph/function that correlates the sounding/ullage to the amount of fluid in the tank. These are generally referred to a "tank capacity curves" if graphical or "Ullage tables" if not.
    Physically however, there is a point where, for most ships tanks, the pump is unable to draw suction. Generally, a well laid out sounding tube will end right next to this suction inlet. As a designer, zero (0) sounding should be loss of suction and the "residual" which still has a ullage measurement is the "ullage" left in the tank. This will have a volume, weight, and free surface.
    When inclining a ship, generally the requirement is to "press up" or "pump to residual" all tanks. Because you don't want fluid coming out the vents, and the fact that you can't get suction to completely empty the tank, this leads to the concept of the "working capacity" of any given tank. This is generally between 2 to 5% head space/residual depending on tank geometry meaning "working capacity" is between 90 to 96% of actual tank capacity.
    There are two major exceptions to this that I know of. First, in submarine main ballast tanks, the water left in the tank after blow down is referred to as the "residual water" and carried as a fixed load in the load to submerge calculation. Secondly, in cargo tanks, any product left behind is the loss of real money. In this case, the tanks are "washed" and "stripped" by a secondary system to ensure that all money making cargo is removed.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Indeed, and as you note, it is often contextual too.
    Since when calculating payloads for stability and also powering estimations, the amount of fluid "left" is often referred to as "reserve". And this reserve is typically 5% of the total/max volume available.
    And is considered not to be usable capacity.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    This thread is scraping the bottom of the barrel ! :)
     
  13. philSweet
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    philSweet Senior Member

    Thanks. There are a number of other places where ullage is used for both the unfillable volume as well as the unemptiable volume, and sometimes for the sum of these two. Breweries and distilleries have an ullage allowance that includes head space, angel's cut, devil's cut, and the proverbial bottom of the barrel.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    The unemptiable residue is what has sent a few people into orbit welding tanks. Just need that tiny amount to provide flammable vapours.
     

  15. JSL
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    JSL Senior Member

    With all the experts' input, I hope we can get to the bottom of this.o_O
     
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