As the ship rolls the water will be moved, but a moment or two after the ship. Thus when the ship is finishing its roll and about to turn, the still moving water will oppose the return roll. The water mass thus acts against the roll at each ship movement.
This athwartships tank is sometimes referred to as a 'flume'. The system is considered passive, since the water flow is activated by gravity. A wing tank system arranged for controlled passive operation. The greater height of tank at the sides permits a larger water build-up and thus a greater moment to resist the roll.
The rising fluid level must not however fill the wing tank. The air duct between the two wing tanks contains valves which are operated by a roll sensing device. The differential air pressure between tanks is regulated to allow the fluid flow to be controlled and 'phased' for maximum roll stabilisation.
A tank system must be specifically designed for a particular ship by using data from model tests.
The water level in the system is critical and must be adjusted according to the ship's loaded condition. Also there is a free surface effect resulting from the moving water which effectively reduces the stability of the ship. The tank system does, however, stabilise at zero speed and is a much less complex installation than a fin stabiliser.
Post a Comment