some ships in which the tank is higher than wide, the

As indicated by this formula, the free surface effect

opposite may be true. The normal practice of

varies as the cube of the breadth (b) but only as the first

maintaining the fuel oil tanks 95 percent full takes

power of the length (l). Because of this relationship, a

advantage of the fact that pocketing occurs, at very small

single bulkhead that cuts a compartment in half in a

angles of heel, when a compartment is almost full.

fore-and-aft direction will quarter the free surface

effect.

The athwartship breadth of a compartment has a

great influence on the reduction in GM caused by the

free surface effect. This influence is shown by the

To avoid having to make calculations from the

following formula:

formula given in the previous section, a free surface

effect chart based on this formula is used to find the

b 31

Rise in G

reduction in GM that occurs as a result of free surface.

12(35W)

Such a chart is shown in figure 12-30.

Where b = athwartship breadth of compartment

To use this chart, draw a straight line from the

1 = fore-and-aft length of compartment

a p p r o p r i a t e p o i n t o n t h e AT H WA RT S H I P

DIMENSION scale (A) to the appropriate point on the

W = displacement of ship

C

D

B

A

CHART FOR

500

100

100

FREE SURFACE EFFECT

BASED ON EQUATION

600

90

90

b3 l

700

RISE IN G =

12 (35w)

800

80

80

b = BREADTH OF COMPARTMENT

900

I = LENGTH OF COMPARTMENT

1,000

70

70

w = DISPLACEMENT OF SHIP

E

60

60

1,500

10.0

2,000

50

50

5.0

4.0

3.0

3,000

2.0

40

40

1.0

4,000

.7

.5

5,000

.4

30

30

.3

6,000

2

.2

7,000

8,000

25

25

.1

9,000

10,000

.05

1

.04

20

.03

20

.02

15,000

.01

20,000

10

10

30,000

40,000

50,000

0

10

DCf1232

12-17