A virtual rise in the center of gravity may be caused by __________.
A. filling a partially filled tank
B. using fuel from a pressed fuel tank
C. emptying a partially filled tank
D. transferring ballast from the forepeak to the after peak
A. filling a partially filled tank
B. using fuel from a pressed fuel tank
C. emptying a partially filled tank
D. transferring ballast from the forepeak to the after peak
B. Using fuel from a pressed fuel tank.
ReplyDeleteThis is another question that should be reviewed closely. I believe there is more than one answer. Keep in mind that VIRTUAL RISE is always associated with Free Surface Moments causing a virtual vertical shift in G.
ReplyDeleteLet's see which questions are not good answers ans why.
Choice A. filling a partially filled tank will reduce free surface to zero so there will be no virtual rise.
Choice C. emptying a partially filled tank will also reduce free surface to zero so again there will be no virtual rise.
I agree that Choice B. "using fuel from a pressed (full) fuel tank" seems to be the best answer at first glance, however Choice D. "transferring ballast from the fore peak to the after peak" could also create a virtual rise due to free surface. In this day and age we are not using Rocks for ballast any more!
It seems the authors of this question assume that the Forepeak Tank is full and after the transfer the After Peak tank will be full, but that is a poor assumption. During the transfer of ballast there could be an increase in Free Surface Moment with no change in Displacement due to both tanks being slack. We could end up with more Free Surface Moments and an increase in the virtual rise in the center of gravity.
I would protest this question as having more than one correct answer.
DO YOU AGREE OR DISAGREE?
Good point there may be a difference in fore and after peak tank capacity.
ReplyDeleteThe wording is vague as well, transferring but no mention of empty, pressed, or slack
on those peak tanks.
I was leaning on Bravo until you brought up that point.