Condra has started work on the manufacture of its first seagoing crane, a 2 t, 4-m-span double-girder electric overhead maintenance machine.
The crane, with power-to-motion conversion achieved through rack-and- pinion instead of pure friction, will undertake maintenance work on helicopters and other equipment within a deck-level workshop at sea and in port.
The machine is required to work while the ship is rolling or pitching through arcs of up to 30°, or 15° either side of the vertical, an oscillation that would pose a challenge to conventionally designed long-travel and cross-travel movement, in which motor power is applied to steel wheels and the friction between wheel and girder produces motion.
To meet the design specification, Condra replaced all wheels on the long-travel and cross-travel with rack-and-pinion arrangements that will deliver both traction and stability as the ship moves about.
With any deviation greater than a 30° arc during a storm, work in the workshop will stop and the crane will be secured through its bottom-block to a structural girder on the workshop’s walls to make accidental movement impossible.
In addition, 440 V three-phase motors will be used to drive the pinions along their racks, maintaining a constant speed and countering the varying gravitational component, while the vessel rolls and pitches.
“The design of the crane proved interesting, not only because of the need to use rack-and-pinion drives, but also because of the very tight installation parameters within the vessel’s workshop, where ventilation pipes impose limits on the available space, and where careful design of the crane’s structure was needed to allow the hoist to be situated almost touching the workshop roof, thereby providing maximum lifting height,” says Condra MD Marc Kleiner.
The resulting design is an underslung crane attached to the gantry beam rather than to the gantry columns.
“With the hoist sitting astride the underslung girders, we are able to give the customer the lifting height that he wants,” he says, noting that it is a compact, but very effective arrangement.
Condra will deliver the seagoing crane within a few months, after which technicians will carry out the installation and commissioning in Durban at a much later date that is convenient to the customer, probably towards the end of the year, when the vessel returns to harbour.