TTS Review 6 - TTS Group ASA

Linkspans
The Stena Line relocation project
Specialists from TTS Port Equipment are close to completing one of the most extraordinary
relocation projects in the history of the marine industry
Technical manager Mikael
Jimmerfors takes us through the
story. “Eleven or twelve years ago,
while working for a different company,
we designed six linkspans for Stena Line’s
HSS fast ferry services. These linkspans
form an integrated part of the vessel, and
are designed to minimise turnaround
times and reduce fuel consumption. The
linkspan concept has been a great
success – Stena is able to load or unload
1,500 passengers, as well as cars and
buses, in 15 minutes.”
The linkspans, which are semisubmersible,
measure 40m long by 40m
wide and weigh over 1,000 tonnes, were
installed at the terminals for Stena’s
Holyhead–Dun Laoghaire, Belfast–
Stranraer and Harwich–Hoek van Holland
routes. However, Stena recently decided
to close down the latter service and came
to Jimmerfors and his colleague, project
manager Klaes Lundberg, now working
for TTS, for help with the linkspan.
“The linkspans installed in Harwich
and Hoek van Holland were newer, and of
an upgraded design,” says Lundberg. “So
Stena simply asked us if we could move
them to Scotland and Northern Ireland
for use on the Belfast–Stranraer route.”
This was a challenge. When the
linkspans were originally installed, giant
floating cranes were used to lift them
into place. These particular cranes,
though, are now deployed elsewhere
around the world. “To lift them with
cranes wasn’t practical, because the best
window the crane company could give us
was ‘The first or second half of the year.’
But we only had a one or two week
window to do the work!” says
Jimmerfors.
4 TTS Review • April 2008
So the TTS engineers decided that the
best alternative was a skidding and jackup
operation. Using a giant North Sea
barge as the main jack-up platform and
transport vehicle, they had to get the
outer end of the linkspan on to the barge,
then remove the pontoon from the
linkspan – essentially by cutting off its
legs. This made the pontoon extremely
unstable, another challenge given the
three-metre high tide, six knot tidal race
and the wake from ocean-going vessels
coming in and out of the port of
Rotterdam every five minutes. “The work
was precision – landing the linkspan on
the barge and releasing it from the bank
had to be accurate within millimetres,”
says Lundberg. “When it came to
Positioning the barge to support the linkspan
before removal of the underwater pontoon
“
The trickiest part
was the handling
of the submerged
pontoon – it
weighs 150 tonnes
and we had to
bring it through
the surface of the
water, which
completely
changed its
stability
”