Settling Tanks

Discussion in 'Boat Design' started by JCL Design, Feb 13, 2021.

  1. JCL Design
    Joined: Feb 2012
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    JCL Design Designer

    Looking for some help of settling tank desing. Any input on what the required slop at the bottom of the tank should be to help draining of the dirt and water that collects at the bottom? Also any info on the design of the baffles would also help.

    Thanks
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I presume that this is for a settling tank for fuel on a ship - approximately how big does the tank have to be?
    If for a ship, I presume it will be a steel tank?
    Re baffles, they would normally be part of the structure, and you should be able to use Class rules for an initial estimate of what is required?

    Or is this tank for a small(er) craft rather than a ship?
     
  3. JCL Design
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    JCL Design Designer

    Thanks it is a steel ship and its about 80m3. I will ues the rules as per class but just wondering if anyone had a standard or rule of thum regarding these aspects to help with settling. Do you have any idea on the slop at the bottom of the tank I was thinking about 15degrees but was not able to find anything in the rules or other ref matrial.
    Thanks
     
  4. JCL Design
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    JCL Design Designer

    And yes its a fuel settling tank.
     
  5. jehardiman
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    jehardiman Senior Member

    Are you also going to have a sludge and day tank? There would be a some differences depending on the fuel system arrangement need.
     
  6. JCL Design
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    JCL Design Designer

    yes we would need both.
     
  7. jehardiman
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    jehardiman Senior Member

    Is your tank going to be against the shell? Because one of the easiest things to do is make them wing tanks, and the turn of the bilge takes care of the issue. By not returning what is stripped in the fuel separator/filter back to the settling tank, you won't have to strip the settling tank as often.
     
  8. JCL Design
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    JCL Design Designer

    No I was going to have the tanks on close to the centerline to help reduse the motion and allow for better settling in the tank. I'm mailing wondering if there is a standard fro the slop at the bottom of the tank as I have not seen anything in the rules or in other reference material.
     

  9. jehardiman
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    jehardiman Senior Member

    Ok, basically it's going to come down to your actual fuel selection, its analysis, and the shape of your tank. How much water and sediment (heavy oil/tar/sand) are you getting in your bunker? How often do you want to strip and/or clean the tank? Generally in the US, fuels have ASTM requirements for water and sediment (ASTM-D1796), so No. 2 Diesel (ASTM D975) allows 0.10%, but No. 4 allows 0.50%. So you need to work out how much is going to accumulate between overhauls and keep that volume below suction, trusting the fuel system to pass any that gets into the header to be taken out by the sludge tank which can be conveniently emptied.
     
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