LONGITUDINAL DIMENSION scale (B); this line
will intersect the pivot scale. Then draw a second
straight line from the point of intersection on the pivot
scale (C) to the appropriate point on the displacement
scale (D). The point at which this second straight line
intersects the GM reduction scale (E) gives you the
reduction in GM (in feet) that is caused by the free
surface.
For example, assume that you want to find what
reduction in GM is caused by free surface effect in a
partially flooded compartment that is 35 feet athwart
ships and 20 feet fore-and-aft, in a ship of 10,000 tons
displacement. Draw the first straight line from the
35-foot point on the athwartship dimension scale to the
20-foot point on the longitudinal dimension scale.
Then draw the second straight line from the point of
intersection on the pivot line to the 10,000-ton point on
the displacement scale. The point at which the second
straight line intersects the GM reduction scale
indicates how much reduction in GM has occurred
because of free surface effect in the partially flooded
compartment. In this example, GM has been reduced
0.2 foot.