THE MARINE INDUSTRY SPECIAL FOCUS
Reliably crossing the Solent
Accelerometers from Monitran have been selected for a new hovercraft that will be crossing the Solent up to 70 times per day, enabling the operator to receive early warning of any mechanical problems. Andy Anthony, managing director, explains
A
hovercraft is an extremely versatile marine vessel. Not only is it capable
of operating over almost any flat surface, including shallow water and ice, but it can traverse vegetation, logs and debris, making it suitable for a variety of harsh-environment roles such as search and rescue. Hovercraft are also used for passenger ferry operations, where they have the advantage of being able to come ashore for loading and unloading, and they are unaffected by low tides. The latest hovercraft to be
Two accelerometers are attached to the lift fan pulley bearings
manufactured by Southampton-based Griffon Hoverwork is the 12000TD. One of the most technically advanced and modern hovercraft in world, this features a highly integrated lift and thrust system, driven by two MAN D2862 diesel engines, which gives it a top speed of 50knots. Sister company Hovertravel is looking to operate two craft this Summer for its Solent crossing service, which operates between Southsea, Portsmouth and Ryde on the Isle of Wight. Established in 1965, Hovertravel is the world’s longest
running commercial hovercraft operator. As well as being the first customer for the 12000TD, Hovertravel was used as a case study to help define the specifications for the new craft. Mark Downer, Griffon Hoverwork’s
chief engineer, comments: “Passenger ferry services have to be both low cost and reliable, requirements which force you to make a certain ‘weight-versus- ruggedness’ compromise when designing a hovercraft.” Downer goes on to explain that fuel savings come from a lightweight design but that reliability is traditionally achieved through the use of extremely rugged components, which tend to be heavier as they are made with smaller allowable load factors. “Lighter components can be used to
achieve the same levels of reliability, provided maintenance schedules focus on those components. However, even with a short-interval time-based maintenance schedule you cannot mitigate against failures occurring between inspections – which would have an adverse effect on hovercraft availability. It is much better to constantly monitor the rate of wear of the components so that they can be changed when they reach their limits.”
PREDICTING WEAR For the 12000TD, it was therefore decided to adopt a condition-based predictive maintenance (CBPM) strategy. It is underpinned by on-board equipment that monitors vibration levels on the craft’s two drivetrains (one for port side one for starboard) and a shore-based HMI to enable engineers to fine tune their
30 APRIL 2016 | DESIGN SOLUTIONS
maintenance schedules against the actual wear of components. Downer continues: “Another advantage of having continuous, on- board condition monitoring, is that if a drivetrain component were to suddenly fail then an alarm can be raised immediately to warn the pilot. The pilot doesn’t need to know the nature of the fault, just that there is one.” The on-shore maintenance team,
which has access to real-time data, can also be notified. This allows the team to commence preparations before the hovercraft even lands and hence guarantees the quickest possible return to service. For the on-board vibration monitoring system, Griffon Hoverwork turned to Monitran, the UK-based designer and manufacturer of sensors and monitoring systems. In 2012, Monitran designed and supplied systems for monitoring the drivetrains of 12 8000TD hovercraft, ordered by the Indian Coast Guard for border patrols. Downer recalls: “For that project, the focus was on warning the pilot if the drivetrain experienced any abnormal vibrations. For commercial passenger services, whilst rough seas can be experienced, the focus is more on developing a predictive maintenance schedule. The ability to warn of abnormal loading is an added bonus.” Downer goes on to say that
Hovertravel’s craft will be making the 10-mile Solent crossing up to 70 runs a day during peak season, so maintenance is essential to assure the operational fitness of the craft. In addition, if the
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