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