PRACTICAL
for launching. The carriage could then be
tilted to enable the lifeboat to slide into the
water, or be moved into deeper water so it
could fl oat off.
According to manufacturing manager,
Dan Sharp, the beauty of the water jet
propulsion systems is the shallow-water
manoeuvrability, aided by the fact that the
Shannon’s draught was to be just 0.98m.
‘With the exception of side keels, there
aren’t any other appendages hung from
the hull, such as propellers, propeller shaft
brackets and rudders,’ he adds.
Following the Experimental Boat trials,
the project team still needed to identify the
ideal hull form, so tested some options
from France and Ireland.
“At the time we were looking outside the
RNLI for a suitable hull design, and invited
proposals from naval architects,” says
Dan. “One of our former naval architects,
Peter Eyre, also put forward a hull shape
for us. We had six design proposals
altogether.”
Vigorous testing
Normally it would take the RNLI around
fi ve years between agreeing the boat
requirements to having the fi rst of a new
class on station. However, with the
Experimental Boat falling short of
expectations, additional time was required
to allow for the new hull design and
testing. By 2009 the team had six^1 ∕ 8 scale
models ready for testing with water jet
propulsion, as well as a model of the
Experimental Boat for comparison
purposes. A further programme of testing
took place, involving towed and free-
running tank tests in which models can be
subjected to controlled wave conditions in
a large water-fi lled container for
observation, and open-water trials in
Poole Harbour. In fact, it was among the
most extensive series of evaluations ever
conducted by the RNLI.
Trials on the models included measuring
pitch, roll, yaw and vertical behaviour as
well as transverse and longitudinal
acceleration. The data was matched
against video footage of the models in the
water and the view as seen by the
coxswain using a tiny onboard video
camera. From these evaluations the team
selected two models and then picked the
best. This turned out to be the proposal
from Peter Eyre, which became the RNLI’s
fi nal choice for the Shannon. Berthon of
Lymington was selected as the boatbuilder.
“Over the years the Institution has
worked with several boatbuilders involvingvarious lifeboat classes, and the yard
which best understands our needs and
how we operate is Berthon,” explains Dan.
“They were responsible for building
earlier lifeboats and their boatbuilding
skills are exemplary. They were involved
with the Shannon design project from the
outset helping considerably in producing
the fi nal boat.”
Meanwhile, production of the RNLI’s
advanced composite hulls, which had
been made by Green Marine in
Lymington, was taken over by a new
company called SAR Composites, an
RNLI subsidiary.Deck and superstructure use carbon fi bre
for lightness and strength
ABOVE Scale models were used for tank testing of different hull designs. ABOVE RIGHT Hull is created via a vacuum infusion process
A new Shannon
deck and
superstructure
(foreground) is
under construction
while Severn-class
lifeboats undergo
a refi t