Supacat provides rescue remedy
The design of an innovative lifeboat launcher presented a series of unusual challenges.
Manufacturing a vehicle that can launch an 18-tonne lifeboat in minutes and be fully submersed under 9m of water was always going to be a challenge. But after nine years of development, vehicle maker Supacat is getting ready to put the Royal National Lifeboat Institution’s (RNLI’s) Launch & Recovery System (L&RS) into production.
The system comprises an automated hydraulic tractor and carriage in the familiar RNLI orange and blue, designed to carry the Shannon-class lifeboat to the water’s edge at beach sites without a launch jetty. Once a mission has been completed, the boat can be picked up from a beached position and turned around ready for relaunch within about five minutes.
Even for a company used to dealing with very specific requirements, Devon-based Supacat faced a particularly tricky set of issues it hadn’t tackled before in the L&RS, not least because the design was such an upgrade of the RNLI’s existing system. But with some inventive engineering and contributions from a largely British supply chain, the company was able to make this unique vehicle a practical reality.
‘We started from a clean sheet of paper,’ said project chief engineer Simon Turner. ‘Not particularly experienced in handling boats but keen to lend our hand to anything we can that’s innovative, we came up with various solutions and after a while we focused on one in particular.’
Instead of using a distinct towed trailer like the old launcher, Supacat developed a four-track drive design where hydraulic motors power both the tractor and the rear carriage, which is connected by a pivoting swan neck and is mounted on a slewing bearing that allows 360º rotation.
‘We were trying to find a way of preventing us having to mimic the current system where the tractor has to disconnect from the trailer to recover the boat, because it extends the recovery time substantially, and there’s also a risk in doing that,’ said Turner. ‘[If there’s a problem reconnecting] then you’ve suddenly got an immobilised trailer, potentially with a boat half recovered that you can’t do anything with.’
The solution was giving the carriage’s tracks permanent drive power but, owing to the vehicle’s articulation, this required a complex hydraulic system provided by Bosch Rexroth to control the movement of the rear tracks in response to those of the tractor (see box). ‘With an articulated vehicle, as you turn, all four sets of tracks rotate at a different speed because they’re each following a different radius,’ said Turner.
There was also a challenge in creating the rotating cradle on top of the carriage that enables the boat to launch and return bow first. This was seen as critical for the boat’s recovery time and allows the system to be operated with just two people (including the driver).
‘The technical challenge is being able to haul the boat into a position where everything is perfectly balanced,’ said Turner. ‘You’ve got a very large boat being spun around in mid-air and it needs to be safe for the crew and potential casualties on board when this is happening.’
But perhaps the most all-encompassing issue was equipping the vehicle for the marine environment, enabling it to stand up not only to the pounding waves but to complete submersion - just in case it becomes stuck in the sand and the tide comes in. This involved keeping the water out of part of the vehicle while enabling other components to function when wet. ‘Certainly from the point of the cab and the engine bay, it’s very important to keep the water out because there are some very expensive, complex systems in there,’ said Turner. ‘As for the rest of the main structures, they’re either completely sealed from the environment or completely open to it so the water can wash in and wash out again.’
This was a key area where Supacat made use of its suppliers, many of whom came from the coastal south-west part of England. ‘Where possible we have used suppliers that have experience of the [marine] environment,’ said Turner. ‘Where they haven’t, we’ve introduced them to our knowledge and experiences. Paint and corrosion protection systems are key on this, particularly as it’s going to be in service for up to 50 years.’
One of the key suppliers in this area was Portland-based Perryfields, which provided a painted corrosion protection system for some of the vehicle’s steel parts. It used a zinc spray followed by a polyurethane paint to provide an attractive finish with strong corrosion resistance on parts of the structure that were too large or too intricate to be galvanised.
Source: RNLI/Kevin Riley
Much of the high level of marinisation was introduced as the vehicle went from a prototype to the pre-production standard model that Supacat has today. The original version used an off-the-shelf track system provided by a US company as a way of showing how rubber tracks would work to disperse the 50-tonne weight of the fully loaded vehicle. When the company’s owner retired, Supacat bought the rights to the design and made it suitable for a marine environment to ensure low maintenance.
The wheels were also redesigned to reduce maintenance, replacing oil-filled hubs and tyres with single-piece rubber mouldings provided by Gloucestershire-based Custom Moulded Polyurethane (CMP). ‘We’re using [polyurethane] as much as we can for longevity, lower maintenance and reduction in cost,’ said Turner. ‘It’s experience that [CMP] has had before with other track vehicles, and we’re learning from the company how to apply that to this application on a much bigger scale than it would be used to before.’
Changing material also allowed Supacat to improve the design of the tractor’s cab, working with the RNLI’s subsidiary SAR Composites. Replacing the previous steel frame with a composite version allowed the engineers to design the cab much more flexibly. ‘There’s no corrosion to worry about as such and it’s allowed us to have much bigger windows so that visibility and all-round awareness is increased no-end,’ said Turner.
The other major change was moving from a Mercedes V6 engine to power the hydraulic motors to a more powerful 331kW model provided by Scania (see box). This also meant altering the configuration of the engine bay to accommodate the taller, narrower engine. ‘We’ve had a lot of repackaging to do but we’ve ended up with a very nice, tidy engine installation as a result with good commonality of parts,’ said Turner.
Supacat has been contracted to manufacture four vehicles following final compatibility trials with the prototype Shannon lifeboat and the RNLI is hoping to commission a further 16. With luck, this uniquely British engineering project will be seen navigating some of the UK’s most demanding beaches from next year.
supplierprofile: Bosch Rexroth
Supacat looked to Bosch Rexroth to supply the vehicle’s automatic hydraulic control systemBosch Rexroth was one of the suppliers with whom Supacat worked most closely on the L&RS due to the vital importance of the hydraulic control system that automatically manages the movement of the two parts of the articulated vehicle.
‘Bosch Rexroth was more than willing to be involved with us, work with us, offer us its experience on similar programmes and, where it didn’t have a product that was suitable, was willing to adapt or design something that could provide the capability we needed in the system,’ explained Supacat’s Simon Turner.The company had worked on similar vehicles for the defence sector and had experience in the marine and offshore arenas. But to put its algorithms to the test, the team built a 1/24th scale model of the vehicle rather than relying on computer simulations. ‘In doing this, we could integrate our control systems, electronics and drives,’ said Bosch Rexroth’s systems and engineering manager. ‘Then, using true-to-life scale caterpillar tracks we could prove that we could actually run over differing terrain and differing traction requirements to put the power down to get this vehicle as mobile and agile as it should be.’
An engine provided by Scania automatically powers the propulsion and launch systems
After the prototype L&RS vehicle’s engine became obsolete, Swedish industrial vehicle and engine manufacturer Scania was chosen to supply the new model thanks to its prior links to the RNLI. The core engine that Scania eventually provided to power the vehicle’s hydraulic propulsion and launch systems was identical to the one on the Shannon-class lifeboat, said Ray Johnson, general manager at Scania Engines.
‘So if you train the engineers up on the base engine on the marine, then they should readily recognise the engine as it is in the Supacat vehicle,’ he added.Because of the bespoke nature of the vehicle, Supacat designed a separate cooling system for the engine, positioned around the 1.2m-diameter circular tube to seal the engine off completely from the marine environment.
‘The unit had to fit into the existing engine compartment and interface with the existing hydraulic transmission ideally without driving any change in the position of the transmission,’ said Supacat’s Simon Turner. ‘This was achieved, although it meant that other systems had to be altered to suit, such as the exhaust system, batteries, the air cleaner and charge air pipes.’