New hull design for latest RNLI lifeboat

Members of the FCB2 project team with members of staff from Seaspeed Marine and the hull models. Photo courtesy of RNLI

The development of the latest all weather lifeboat for the UK&rsquo

Designated FCB2 (Fast Carriage Boat 2), the charity’s latest all weather lifeboat will gradually replace the Mersey class lifeboats first introduced in 1988. The Mersey class can be launched from a slipway or lay afloat at a mooring or pontoon but is mainly intended for stations without such facilities where the boat is housed ashore on a carriage and launched by an immersion proofed tractor.

For FCB2, the RNLI has started with a clean sheet of paper for the boat and worked with Devon based Supacat to redesign the launch and recovery system. An important operational change is an increase in speed from 17 to 25 knots, in line with the Tamar, Severn and Trent class RNLI lifeboats.

Following extensive trials conducted by the RNLI, another significant decision is to adopt water-jet propulsion for the new boat. This will make it the charity's first all weather lifeboat with such propulsion.

In 2008, rough weather trials proved that the performance of the experimental FCB2 boat’s original hull design in rough seas did not meet the operational requirements for an RNLI lifeboat, especially when travelling up sea in short steep waves. This resulted in a requirement to identify a new hull form. Several potential designs, including existing commercial hulls, bespoke concept designs and an in-house design were considered.

Five hulls were chosen and eighth scale models were built and subjected to rigorous comparative trials in both open water and test tank conditions. The trials were conducted by Seaspeed Marine Consulting Ltd at the QinetiQ ocean basin and ship tank facility in Gosport as well as open water in Chichester and Poole harbour.

Up sea performance was investigated using the ship tank facility in both free running and towed configurations and the ocean basin, complete with wave machine, allowed vessel handling and down sea performance to be compared. Finally, open water trials of the models compared performances in rough weather conditions. Data for the boat’s pitch, roll, yaw and vertical transverse and longitudinal accelerations was recorded together with both external and internal video. All this information was compared with data from the experimental lifeboat and the existing Mersey class.

Following analysis of all the data by the Project Team, and input from the Technical and Operational Departments, the RNLI has now decided that the in-house design is best suited for FCB2. The hull was designed principally by Peter Eyre, an RNLI Naval Architect, who felt that the knowledge and experience from the in-house designed Tamar, Severn and Trent class lifeboats could be put to good use. Peter commented, ‘The RNLI has an extensive history in the development and build of lifeboats so it made sense to accumulate all this information and knowledge to develop an in-house design for FCB2.’

SAR Composites, an RNLI subsidiary company, will now be building the hull and wheelhouse for a full size prototype to be fitted out at a commercial boatyard, yet to be announced. Trials are expected to commence in 2011.

The concept of using water-jets on a modern all weather lifeboat has already been proved following extensive trials and the prototype is to be powered by Scania engines driving Hamilton water-jets.

In parallel with the development of the boat itself, a redesign of both the concept and the applications of the launch and recovery method to improve both safety and efficiency of the operation have taken place. Devon based Supacat Ltd design and build high mobility, all terrain vehicles and have now been awarded the contract to design and build the pre-production launch and recovery system for FCB2, comprising a tractor and powered carriage arrangement.

By Peter Barker

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