Question

With reference to activated fin stabilizers give reasons why:

(a) For large vessels such units are preferred to passive tanks. (6)

(b) These units are preferred for passenger and fast cargo ships, (6)

(c) Partial rather than maximum damping of ship movement in heavy weather is advisable for reasons other than overstressing of fin stocks and activating gear. (8)

Answer 1

Part (a)

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 900 m3, 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.

Part (b)

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.

Part (c)

In heavy weather, the speed of the vessel is reduced. The harder the fins work in trying to damp the movement of the vessel, the greater the reduction in speed, which reduces the stabilisation effect. If the damping of the vessel is maximised using the stabilisers, the vessel becomes stiff, and the resulting jerky movements make it far more uncomfortable than if the vessel is allowed to gently roll.

✓ Verified Model Answer (Text Solution)

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 900 m3, which equates to approximately 20 containers.