Stena Discovery Performance Improved With Enhanced Steering System

On February 14, the world's largest high-speed ferry catamaran Stena Discovery took off from Belfast, after a planned drydocking, and about one hour out at sea on the captain's command the waterjet control was switched over to steering by a retrofitted Humphree Interceptor Steering System. While the interceptors engaged and provided the means for directional control of the vessel, the steering buckets of the four Kamewa 160 SII waterjets. in total absorbing a power of 68.5 MW, automatically returned to their neutral, or boost position, allowing all waterjet thrust to be vectored forward for maximum thrust, and eliminating the waterjet bucket drag.

During transit to Hook van Holland in the Netherlands, a series of trials confirmed supreme performance of the Humphree interceptor steering system.

The turning response of the vessel with the steering interceptor system active was described as faster and the general turning behavior compared well with that of four waterjets steering up to the bucket steering angle equivalent to full interceptor stroke. When passing the Land's End of England with quartering following sea and a significant wave height of about 10 ft. (3 m), the Captain concluded that the interceptor steering system indeed worked fine and that the vessel was notably faster. In moderate sea at a vessel speed of 40 knots, the reduction of speed when steering with the interceptors was significantly reduced. The gain was recorded to one knot, or three MW in terms of delivered power. As the improvement is increasing with increasing sea state — the annual fuel saving is expected to be quite substantial. In addition, the auxiliary power requirement was reduced from about 120 kW to 4 kW, which adds up to an additional yearly fuel saving as well as it gives an idea of the mechanical and structural advantages of using Humphree interceptor units as control devices, whether they are used for steering or active damping of ship motions.

The patented Humphree interceptor steering system has been developed and delivered by the marine division of LA.ME., which is an Italian-Swedish joint-venture with electro/mechanical engineering and production in Milan and sales and hydrodynamic expertise in Gothenburg. The steering system comprises of four (two on each transom) compact hydraulically operated HV160 vertically mounted Humphree interceptor units, two hydraulic power packs, one in each hull, and a main control system unit for manual operation and ship system integration. The steering interceptor system is fully integrated into the main steering system, including the autopilot, waterjet control system, and the ship's integrated monitoring system. When the interceptor steering system is active, the steering command operates only the interceptors to their maximum stroke, while if further steering is needed the waterjets are requested to engage and be deflected to add steering force. In rough seas, or should an emergency situation occur, the captain will have the joined force of full interceptor steering and full waterjet steering, resulting in significant fuel savings and/or improved safety at sea. Humphree Interceptor Steering Systems are designed to offer owners of high-speed vessels a unique means to increase maintained vessel speed and/or lowering fuel bills and reducing the environmental impact on sensitive routes.

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