Sample Free Surface Correction Problem SS American Mariner

The SS AMERICAN MARINER is ready to bunker with drafts of FWD 15′-05″, AFT 21′-03″. After all bunkers are on board, soundings indicate the tonnages shown.

Use the white pages of The Stability Data Reference Book to determine the free surface correction.

  • Answers:
  • A. 1.05 feet Incorrect.
  • B. 1.15 feet Correct.
  • C. 1.25 feet Incorrect.
  • D. 1.31 feet Incorrect.
  • Step 1:
  • Calculate Mean Draft.
  • 15′-05″fwd + 21′-03″ aft = 36’08”
  • Mean Draft: 36′-08″/2
  • Mean Draft = 18’04”
  • Step 2:
  • Using the Hydrostatic Properties table (Sheet 3) for the SS American Mariner (White Pages), calculate the Total Displacement (S.W. Tons) for the vessel before loading bunkers with a mean draft of 18’04”.
  • Step 3:
    • Add up all the bunker totals for each tank. The sum of all bunkers equals 3024.8 tons.
  • Step 4:
    • Add the displacement of the vessel before loading the bunkers and the sum of all the bunkers to find the ship’s final displacement.
  • 12,000 tons + 3024.8 tons = 15024.8 tons
  • Step 5:
    • Refer to the Table for Free Surface Correction and Tank Capacities (Sheet 4) to calculate the free surface moment for each tank. On the S.S. Mariner , a tank is considered FULL if the tank is at least 97% full. Any quantity less than 97% full or an empty tank is considered SLACK.
  • In the column F.O. Tons under Tank Capacity, the table gives you the capacity of each tank at 97% full. This is the column you will compare your loaded bunkers in each tank with to verify if a tank is considered FULL or SLACK. For example, DB 1 CL is loaded with 48.2 tons of bunkers. The tank capacity at 97% for D.B. 1 CL is 48.2 tons. Therefore, the tank is considered FULL and its free surface correction is 67. Conversely, D.B. 4 CL is loaded with 208.6 tons of bunkers. The tank capacity at 97% for D.B. 4 CL is 224.1 tons. Since 208.6 tons is less than 224.1 tons then D.B. 4 CL is considered SLACK.

Now find the free surface moment for each tank.

  • Next, find the total sum of free surface moment which equals 17,309 foot tons.
  • Step 6:
  • Find the free surface correction in feet by dividing the total free surface moment by the final displacement of the vessel.
  • FS(corr) = 17,309 foot tons/15,024.8 tons
  • FS(correct answer) = 1.15 feet

There are 19 questions in the online study on this subject under.

  • Deck Department
  • All Deck Examination Questions As of March 24, 2014 Regulations
  • Deck General – Safety
    • Stability and Trim Problems With ST-Tables
      • Free Surface Correction, Mariner Class 
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