Stability – I : Chapter 10

17. A ship of 1000 t displacement has a fresh water DB tank which is 20m long and divided in to P ,S and C watertight divisions . The  P and S division are each 4m wide , while the she division is 12m wide . Calculate the FSC in the following cases :

    1. Only the port side tank is slack .
    2. Both port and stbd tanks are slack .
    3. Only the centre tank is slack .
    4. All three tanks – PS AND C are slack .
    5. If all the three divisions were not separate but formed one undivided tank 20m broad.

NOTE: 1/n² cannot be used here as the watertight division are not identical.

Solution:

a). Only the port side is slack

We can calculate

FSC =   (LB³ x di )/(12 x W)
= (4³ x 20)/( 12 x 10000)
= 0.016m

b). Both P and S tanks are slack

= (2 x 0.016)
= 0.0213m

C ).  Only the centre  tank is slack

= (LB³ x di )/( 12 x W)
= ( 12 ³ x 20) /( 12 x 10000)
= 0.288m.

d). All three tank P, S and C are slack

FSC = (0.213 + 0.288) m
= 0.309m.

e) If all the three division were not separate but forward are undivided tank 20 m broad .

We can calculate as
FSC == (LB³ x di )/( 12 x W)
= (20 x 20³x 1) / (12 x 10000)

= 1.333m.