Features: - Tanker Operator

Damage to propellers caused by
ice and other debris is becoming
an increasing problem, a leading
underwater repair specialist said.
Due to this, some of the repairs have to be
undertaken in ice covered areas, or severe
cold conditions encountered during the winter,
such as ports and harbours located in the
Baltic and Barents Sea.
During the past few months, Belgian
underwater repair specialist Hydrex’s divertechnicians
have carried out propeller
croppings in Antwerp, Ventspils, Kiel and
Bremerhaven.
They were undertaken in severe winter
conditions, but did not restrict the divers from
carrying out their tasks, the company claimed,
adding that they were trained to perform a
wide variety of operations, both above and
below the water level, anywhere in the world.
Having developed different procedures for
different types of damage, the company
claimed that it was “equipped to make the best
out of a bent, or broken propeller”.
Ideally, the in-house developed cold
straightening technique is used, which allows
Hydrex to straighten damaged blades in-water,
allowing the vessel to operate without the
need for drydocking. By using this method,
blades can be restored to their original form,
thereby restoring the propeller’s optimum
efficiency.
TECHNOLOGY – SHIPREPAIR & MAINTENANCE
Propeller repairs in extreme conditions restore efficiency
Propeller blades can become damaged in
ice conditions.
Hydrex divers are trained to work in extreme conditions.
Should a piece of the blade be broken, or if
there is other damage too extensive for
straightening, a blade’s section will be
cropped. In cases where there is an even
number of blades, an identical piece will be
cropped from the opposite blade to restore the
hydrodynamic stability of the propeller. By
undertaken this method of repair, the best
possible efficiency is obtained, the company
said.
Tanker repairs
Examples where cropping was the only
solution included – the two of four blades of a
250 m long tanker, which had been bent too
much to be straightened. They were cropped
by a Hydrex diver-technician team while the
vessel was in Antwerp.
An underwater inspection was performed on
the tanker in order to make a clear assessment
of the damage. The information acquired was
then used to calculate and determine the
correct measurements needed to modify the
training edges of the propeller blades. The two
blades were then cropped followed by the
polishing of the sharp edges of the cropped
areas.
Another tanker, this time an 180 m long
vessel, suffered blade damage in Ventspils.
After an inspection carried out in extremely
icy conditions, it was found that two of the
blades were severely bent and needed to be
cropped. This was subsequently carried out in
accordance with the attending class society’s
surveyor.
Following the successful completion of the
repairs to the tanker, the team then moved on
to a 210 m long containership, berthed at the
same port. Here, it was found that four out of
the five blades were bent too much to be
straightened. Following consultations with all
the parties involved, it was decided to cut all
the propeller blades to exactly the same size
and to re-profile all the blades to their
optimum condition under the new
circumstances.
By undertaking this task, the vessel’s
propeller balance could be restored and its
hydrodynamic efficiency optimised to suit the
power requirements of the engine. This
allowed the vessel to continue to sail until its
next scheduled drydocking when permanent
repairs will be performed.
Also in icy conditions, a 180 m
containership berthed at Kiel, needed to have
all four blades cropped after three of them
suffered damage. The blades were modified
one by one. The area to be cropped was
marked out on each blade and verified. Each
blade was then cropped and its edge grinded
to give the correct radius. When the cropping
was complete, the blades were polished to
ensure that any loss of power was minimal.
Further south, in Bremerhaven, another
containership suffered damage to all five
blades. Due to a strong current and very bad
underwater conditions, the cropping of the
blades could not be undertaken underwater.
Therefore, the vessel was trimmed
sufficiently to bring the blades out of the
water, after which they could be cropped to
restore the vessel’s efficiency.
June 2010 TANKEROperator 53
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