Inclining Test Using Double Bottom Tanks

Discussion in 'Stability' started by naserrishehri, Jul 28, 2013.

  1. naserrishehri
    Joined: Jun 2006
    Posts: 206
    Likes: 1, Points: 18, Legacy Rep: 10
    Location: iran bushehr

    naserrishehri Senior Member

    DEAR FRIENDS
    Is it possible to use double bottom tanks as per attached file for inclining test ?
     

    Attached Files:

  2. gonzo
    Joined: Aug 2002
    Posts: 16,790
    Likes: 1,714, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    What are you specifically testing for? I assume you are looking at increasing displacement by filling water tanks in the bottom.
     
  3. naserrishehri
    Joined: Jun 2006
    Posts: 206
    Likes: 1, Points: 18, Legacy Rep: 10
    Location: iran bushehr

    naserrishehri Senior Member

    I'm going to use double bottom tanks for inclining test .
     
  4. gonzo
    Joined: Aug 2002
    Posts: 16,790
    Likes: 1,714, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    OK, but what is the reason for the double bottom tanks? The drawing shows a double bottom that is flooded with water.
     
  5. athvas
    Joined: Feb 2013
    Posts: 156
    Likes: 1, Points: 0, Legacy Rep: 16
    Location: india

    athvas Senior Member

    Do u want to use the double bottom tanks as inclining weights?
     
  6. naserrishehri
    Joined: Jun 2006
    Posts: 206
    Likes: 1, Points: 18, Legacy Rep: 10
    Location: iran bushehr

    naserrishehri Senior Member

    yes. i want to use ballast water as inclining weights .
     
  7. jehardiman
    Joined: Aug 2004
    Posts: 3,762
    Likes: 1,152, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    NO!

    That is a good way to to have another COUGAR ACE!

    Not only to you not know the exact weight and centers, you introduce free surface in the middle of the experiment.
     
  8. TANSL
    Joined: Sep 2011
    Posts: 7,369
    Likes: 699, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Although I do not like the idea, I am unable to say why I do not like it.
    Of course, you must absolutely avoid free surfaces. To find the added weight and center of gravity enough to have tanks sounding tables. I do not think that's a problem.
     
  9. jehardiman
    Joined: Aug 2004
    Posts: 3,762
    Likes: 1,152, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Have you have actually metered a tank? It is not as clear cut as you seem to think and capacity curves can be off by tons. And that is just from temperture-density issues. The necessary accuracy needed for a proper inclining will never be achieved by using the ships own tanks.
     
  10. ldigas
    Joined: Feb 2011
    Posts: 189
    Likes: 5, Points: 18, Legacy Rep: 60
    Location: Zagreb, Croatia

    ldigas Senior Member

    Temperature does not affect mass. It affects density and volume as a result of that, but mass stays the same.

    And although not the most precise solution, water ballast is used in inclining tests where solid weights are deemed inpracticable. However, some precautions are to be taken to ensure the test is properly conducted.
    Talking about large commercial vessels here.

    Something on that
    http://www.veristar.com/bvrules/B_3_a1_1_1.htm
    (ch. 1.1.2 I believe)
     
  11. TANSL
    Joined: Sep 2011
    Posts: 7,369
    Likes: 699, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    jehardiman, the first thing I said was that I do not like the idea but you will have to give me some reason to convince me that it can not be done this way.
    I do not know if you know that in order to properly achive an inclining test, among other things, water density should be measured at a depth equal to half the draft of the boat. I do not know if we have a hydrometer, why can not we use it with the liquid in tanks.
    The volume of tanks, in any boat, is well known. The errors due to temperature may occur (what are these errors?) will not be greater than those produced with the total volume of the ship.
    So, I'm hoping that you show us reasons not to carry out the test this way, but for now, I do not see them. I'm not saying do not exist, but you should try a bit harder.
    Cheers.

    PS : One reason I can think that it is not feasible to use the double bottom tanks is because the heeling moment produced by them is not enough to heel the boat 2 or 3 degrees as required.
     
    Last edited: Mar 5, 2014
  12. TANSL
    Joined: Sep 2011
    Posts: 7,369
    Likes: 699, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I think I've found a reason to not do the test with the double bottom tanks: it is impossible to determine the zero point for measuring the deviation of the pendulum.
    What do you think?
     
  13. naserrishehri
    Joined: Jun 2006
    Posts: 206
    Likes: 1, Points: 18, Legacy Rep: 10
    Location: iran bushehr

    naserrishehri Senior Member

    why impossible?
     
  14. TANSL
    Joined: Sep 2011
    Posts: 7,369
    Likes: 699, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I do not see how to do it without changing the displacement of the boat at some point. How you thought you get it?. Tell me about your procedure, please. DonĀ“t forget free surfaces.
     

  15. naserrishehri
    Joined: Jun 2006
    Posts: 206
    Likes: 1, Points: 18, Legacy Rep: 10
    Location: iran bushehr

    naserrishehri Senior Member

    each level of water in double bottom considered as inclining weights .
    free surface effect shall be calculated by software and considered in
    calculations .
     

    Attached Files:

Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.