A vessel's mean draft is 29'-07". At this draft, the TPI is 152. The mean draft after loading 1360 tons will be __________.
A. 29'-09" B. 29'-11" C. 30'-04" D. 30'-07"
A. 29'-09" B. 29'-11" C. 30'-04" D. 30'-07"
Daily License Questions about Ship Stability and Trim: I just think people need to have some knowledge in their heads, professional or otherwise. After 2007 our world has changed due to the advent of Smart Phones. Retaining knowledge is like being able to play a musical instrument, if you do not use it you will lose it! The questions I post with will hopefully help you keep what you already know or remind you of what you should know. William E. George
Parallel Sinkage = the added weight / TPI = an answer in inches
ReplyDeleteIn this case:
The added weight is the 1,360 Long Tons
TPI = Tons per Inch Immersion = 152 LT/inch
So the Parallel Sinkage = 1,360 LT / 152 LT/inch = 8.95 inches or 9 inches
To complete the calculation we need to add the parallel sinkage to the initial mean draft given of 29'-07" because we are adding weight not removing weight from the vessel.
The mean draft after loading = 29'-07" + 0'-09" = 29'- 16' = 30'-04" or Choice C.
Somethings to think about.
1. Most of these license questions assume a WWII Victory Ship. These ships were about 10,000 tons with the draft marks at the perpendiculars so the average of the FWD and AFT drafts was very near to Midships as well as the LCF. So for problems like this very little thought was given to increase in the mean draft by sagging. Also no change in trim was assumed.
2. More modern ships especially those with transom sterns can behave differently because they have different hydrostatic properties as the transom stern submerges, (the LCF moves aft rapidly as draft increases). Most Panamax size ships do not have their draft marks located at the perpendiculars. If you read these "Apparent Drafts" and average them chances are they will not be near midships so hog or sag calculations will be in error. When these "Apparent Drafts" are corrected to the perpendiculars then they become "True Drafts" and their average will result in a mean draft at Midships. See page 23, Figure 1-10 of STABILITY AND TRIM FOR THE SHIP'S OFFICER, 4th Edition.
KEEP IN MIND THE BEST WAY TO COMMUNICATE WITH THE VESSEL IS BY READING ITS DRAFT MARKS AND SOUNDING ITS TANKS! The vessel's loading computer is only connected to the ship's generator.
C
ReplyDeleteCharley is closest at 30-04
ReplyDelete30-03.95