At the end of 2014,
through our sister company, Lankhorst, we at
CASAR received an interesting request to fit the ropes
on a 40-ton AHC articulating
crane of the Dutch manufacturer,
Langendijk Equipment. The crane
is installed on the supply ship
Wildebeest, which serves oilrigs
of the Edison Chouest Offshore
It lifts and lowers loads weighing
up to 40 t, to a depth of up to
3,000 m. In consideration of the
required safety factor 5, the rope
has to have a minimum breaking force of 200 tons. The wires
used to produce the CASAR
Eurolift have a nominal strength
of 2,160 N/mm² and thus
exceed the required minimum
breaking force. It is fitted with a
40-strand hoist rope that is extremely resistant to rotation. The
rope core and the outer strands
are compacted, which gives the
outer strands a greater bearing
surface on the rope core. In turn,
this reduces the compression on
the point of contact and thus also
the risk of inner wire breakages.
The tailor-made deep sea crane
is fitted with the so-called AHC (active heave compensation) technology,
which allows it to operate at depths of up to
3,000 m and in rough seas of force 5, maintaining a safe working load of 10 tonnes.
In order to meet the rough working environment out at sea, the rope wires are made out
of corrosion-resistant material and have a
special lubrication for rope production.
The great length of the rope, spooled in several layers, imposed the greatest requirements
in production tolerance both on the drum
and us as the rope manufacturer. Langendijk Equipment originally planned a 15-layer
drum. At a technical meeting, however, we
persuaded them to reconsider the drum design as even leading drum manufacturers
advise against the use of more than 14 layers.
After the drum design was revised, we now
have a drum that fully spools the entire
3,100 m CASAR Eurolift Ø46 mm. In spite of
this, even “only” 11 layers pose the greatest
requirements on the maximum permitted tolerance of the rope. Even the smallest gap in
the spooling of the rope in the lower layers
can get bigger in every layer and ultimately
lead to the formation of a rift in the upper layers,
into which a whole strand can be drawn.
This is especially critical if the rope structure is
very loose and the lower layers are spooled at
an insufficient tension. This happens anyway
during usage as the crane usually lowers the
load to the seabed and goes back up without
a load, and consequently spools at a low tension.
This makes compression and accuracy of tolerance hugely important during production.