A vessel with a large GM will __________.
A. have more resistance to listing in case of damage
B. have less tendency to have synchronous rolling
C. be less likely to have cargo shift
D. ride more comfortably
A. have more resistance to listing in case of damage
B. have less tendency to have synchronous rolling
C. be less likely to have cargo shift
D. ride more comfortably
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ReplyDeleteB. Lousy Ride though. Snapping upright rapidly due to stiffness.
ReplyDeleteThe best answer is Choice A. A stiff ship has a large GM and more resistance to listing. TRUE!
ReplyDeleteSTABILITY AND TRIM FOR THE SHIP'S OFFICER, 4th Edition, Chapter 13,covers Synchronous Rolling on pages 303 to 304, as well as previously mentioning it in Chapter 5.
"The practical implications of this very important phenomenon will be discussed in more detail here. In the majority of times when a ship rolls violently, it is because the ship's natural rolling period is synchronized with the apparent wave period. And, it is this connection that the case for the moderate or small GM is enhanced. For it is a fact that the wave periods apt to be encountered on the oceans of the world are much more likely to coincide (or nearly coincide) with the rolling period of a stiff rather than with a tender ship. To put it another way, the 9- or 10-second roll associated with a large GM of the usual merchant ship is similar to a great many of the apparent wave periods which the ship will encounter, while the 15- or 16-second roll associated with a moderately small GM will hardly ever find a matching I5-second wave period. See Figure 5-3 in Chapter 5. However, one warning should be given. It is possible that a tender ship may find herself synchronizing, and in this case the resulting rolling can be severe. (Such as the case of a tender ship at sea with extremely large waves on the quarter.) But even in this case, a change of course, speed, or GM is necessary to eliminate the synchronization than would be the case with a stiff ship.
Choice B. FALSE
Choice C. A large GM will have a fast rolling or a Short Rolling Period, however it will also have very large angles of roll. Put these two together and you get large Accelerations on the cargo producing a greater chance to shift due to the rolling forces. F=MA
Choice D. FALSE. Due to the explanation for Choice C. Again See STABILITY AND TRIM FOR THE SHIP'S OFFICER, 4th Edition, Chapter 5, page 94 to 95 "Your Vessel's Rolling Period at Sea"
Remember a GOOD GM is the smallest consistent with safety!
ANS: ALPHA (Slow your roll)
ReplyDelete