Adaptive roll stabilisation of fishing vessels

The objective of the project was to develop an improved form of passive free-surface anti- roll tank, as commonly fitted to many fishing boats. By adding a flow control system to the tank fluid it was intended that the stabiliser would be able to adapt to changes in the ship roll period and loading conditions, in addition to compensating for deficiencies in the tank length or filling depth. The initial control strategy involved a bi-flow scheme, whereby the fluid would flow intermittently at long roll periods and flow continuously but with damped motion at short roll periods. Sea trials of the prototype stabiliser mechanism identified problems with both control methods, which were subsequently combined into an amalgamated form. The final control algorithm used dynamic models of both the ship roll and fluid distribution to evaluate the work done against the roll by variously damped fluid flow. A simulation of the stabilised ship in irregular waves verified the theoretical basis of the method. Although the adaptive stabiliser was primarily developed for free-surface tanks it could be equally well applied to U-tube designs by using air valves to modify the fluid damping.EThOS - Electronic Theses Online ServiceGBUnited Kingdo