Which statement about the free surface correction is TRUE?
A. It is added to GM at light drafts and subtracted at deep drafts.
B It is increased if the slack tank is not on the centerline.
C. It is decreased if the slack tank is below the KG of the vessel.
D. The correction decreases as the draft increases.
A. It is added to GM at light drafts and subtracted at deep drafts.
B It is increased if the slack tank is not on the centerline.
C. It is decreased if the slack tank is below the KG of the vessel.
D. The correction decreases as the draft increases.
D
ReplyDeleteD is the best answer. Let's see why.
ReplyDeleteChoice A is wrong because no matter what the draft the FS correction increases KG and decreases GM.
Choice B is wrong because no matter the location of the free surface on the ship the virtual rise is the same. Do not confuse the weight of liquid in the tank, which is a different subject.
Choice C is worng because no matter the location of the free surface on the ship the virtual rise is the same. Do not confuse the weight of liquid in the tank, which is a different subject.
D is correct as the draft increase so does the displaced volume of the vessel. Because we divide by the displaced volume an increase in displaced volume will reduce FS correction.
FS correction = r[lb^3/12(Displaced Volume)]
Where for Imperial Units:
r = ratio of denisty of liquid in the tank to that of the water the vessel is floating in.
l = length of the tank in feet
b = width of the tank in feet
12 is a constant for rectangular tanks
Displaced Volume = 35 cubic feet/LT multiplied by the displacement in LT
Where for Metric Units:
r = ratio of denisty of liquid in the tank to that of the water the vessel is floating in.
l = length of the tank in meters
b = width of the tank in meters
12 is a constant for rectangular tanks
Displaced Volume = 1.025 cubic meters/MT multiplied by the displacement in MT