) why Bilge keels are considered as an effective
method of roll stabilization in ships 02
b)
what are the types of tank stabilization
03
c) With
reference to fin stabilisers:
Sketch a block diagram showing an
automated control system; (4)
d)With reference to
activated fin stabilisers give reasons why:
i)for large vessels fin stabilisers are
preferred to passive tanks; (4)
ii) fin stabilisers are preferred for passenger and fast cargo ships; (3)
a)
bilge keels
l up to 30%
roll reduction
l cheap and
easy to maintain
l effective
whether making headway or not
l simple in construction
b)
Pure Passive
water movement
controlled by baffle plates or manually operated valves
Controlled Passive
water
movement controlled by air or water valves
Active
water moved
by an impeller or pump
d)
i)Fin
stabilisers require much less internal volume than tank stabilisers and the
internal space taken up by fins is not usually required for cargo. Typically, the space taken by a passive tank
stabilising system is approximately 900m3 which equates to approximately 20
containers.
The
mass of the fin stabiliser system is also very small compared to the
deadweight, whereas passive tank stabilisers take up approximately 1.5% of the
displacement.
Since
fin stabilisers are also much more effective than passive tanks, there is less
chance of cargo movement/damage and crews are more likely to work at optimum
efficiency.
(ii) In
passenger ships, comfort is of prime importance and this necessitates the best
roll reduction system available.
Activated fins are the most effective method of roll reduction
throughout all periods of wave encounter, mainly due to their rapid response
time. There are also considerations of
financial income with regard consumption of food/drink and other
purchases. It has been shown that
excessive ship motions have a marked effect on income.
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