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.
Staying
in control: the RNLI’s Launch and Recovery system is designed to carry
the Shannon-class lifeboat to the water’s edge at various beach sites
without requiring a launch jetty
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.
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.
