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Daily Question for Feb. 20, 2018

If the cause of severe list or trim is off-center ballast, counter flooding into empty tanks will _________.

A. increase the righting moment

B. increase the righting arm

C. increase list or trim

D. decrease list or trim

Comments

  1. Friends of STABILITY AND TRIM FOR THE SHIP'S OFFICERFebruary 20, 2018 at 6:35 PM

    According to the USCG the best answer is D.

    Typically in sever cases if there is enough freeboard, reserve buoyancy, counter flooding tanks on opposite sides or ends should reduce list or trim. Be careful to take the loss of stability due to free surface effects into account. Also consider in the case of a severe list or trim all bets are off using the hydrostatic curves that are based on the following:

    1. No List
    2. On older vessels no trim. On newer vessel the assumed trims of -1, 0, 1, 2, 3 meters
    where - is by the bow and + is aft.
    3. No hog or sag
    4. The draft is located at the LCF
    5. The Assumed water density is 1.025 unless otherwise specified
    6. The vessel is free floating. It is not touching the bottom.
    7. Still Water, static conditions: no waves, no rudder forces.

    For Clarity, Check out your vessel's Capacity Plan. That is the condition the ship is drawn on the plan. It should also list all tanks and their capacity, VCG and LCG. You can think of the Capacity Plan illustrating the "Assumed" or "Pretended" Condition for the vessels hydrostatic data. This is pointed out in the first chapter of STABILITY AND TRIM FOR THE SHIP'S OFFICER, 4th Edition, on page 26 and 27, "Assumptions The Naval Architect or Shipbuilder Made That You Need to Know About." Also see Fig. 1-13 on page 26.

    Let's see why Choices A, B and C are not the best choice:

    Choices A. and B. To increase the righting moment you will need to either increase righting arm or displacement. Righting Arm, GZ, typically is associated with List only. The question address List or Trim. For that reason I would dismiss these choices.

    Choice C. Counter flooding if done properly will decrease List or Trim so I would dismiss this also.

    ReplyDelete
  2. UnknownFebruary 24, 2018 at 4:56 AM

    Delta

    ReplyDelete

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