An oil tanker 24 m wide displaces 25 000 tonne when loaded in nine equal tanks, each 10 m long, with oil rd 0.8. Calculate the total free surface effect with: (a) no longitudinal divisions, (b) a longitudinal centreline bulkhead, (c) twin longitudinal bulkheads, forming three equal tanks,. (d) twin longitudinal bulkheads, the centre compartment having a width of 12 m.
An oil tanker 24 m wide displaces 25 000 tonne when loaded in nine equal tanks, each 10 m long, with oil rd 0.8. Calculate the total free surface effect with:
(a) no
longitudinal divisions,
(b) a
longitudinal centreline bulkhead,
(c) twin
longitudinal bulkheads, forming three equal tanks,.
(d) twin
longitudinal bulkheads, the centre compartment having a width of 12 m.
Reference:
REED'S NAVAL ARCHITECTURE FOR MARINE ENGINEERS (4th edition),
Exercise – 5.12
Solution:
a)
Free surface
effect = (ρf * I/ ρw * ∇) * 9
= (rd*1/12 * LB3 / ∇) * 9
= (0.8 * 1/12 * 10*243 )/(25000/1.025)
* 9
= 3.4 m
b)
With centreline bulkhead, Free surface effect is reduced to one
quarter.
Free surface effect = ¼ * 3.4
= 0.85 m
c)
With twin longitudinal bulkheads and equal tanks, free
surface effect is reduced to one ninth.
Free surface effect = 1/9 * 3.226
=
0.377 m
d)
For the
middle compartment, I1 = 1/12 * LB3 * 9
= 1/12 * 10 * 123 * 9
= 12960 m4
For the 1st
and 3rd compartment, I2 = 1/12 * LB3 * 9 *2
= 1/12 * 10 * 63 * 9 * 2
= 3240 m4
Total I =
12960+03240
= 16200 m4
Free surface
effect = r.d* I/ ∇
= (0.8 * 16200)/ (25000/1.025)
= 0.53136 m
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