The Velle Derrick
Similar in design to the ‘Hallen’ but without use of outriggers. The leads for the topping lift and slewing arrangement are spread by a cross ‘T’ piece at the head of the derrick. A widespread structured mast is also a feature of this rig (Figures 4).
Again it is a single-man operation, with clear decks being achieved while in operation. Generally, the ‘Velle’ is manufactured as a heavier rig and variations of the design with a pivot cross piece at the derrick head are used with multi-sheave purchases to accept the heavy type load.
The ‘Hallen derrick’
This is a single swinging derrick which is fast in operation and can work against a list of up to 15°. They are usually manufactured in the 25–40 tonne SWL range and, when engaged, operate under a single-man control (Figure 3).
Figure 3. Hallen Derrick.
Joystick control for luffing and slewing is achieved by the Port and Starboard slewing guys being incorporated into the topping lift arrangement. Use of the outriggers from a ‘Y’ mast structure provides clear leads even when the derrick is working at 90° to the ships fore and aft line. A second hoist control can be operated simultaneously with the derrick movement.
As a one-man operation, it is labour saving over and above the use of conventional derricks, while at the same time keeps the deck area clear of guy ropes and preventors. Should heavy loads be involved only the cargo hoist would need to be changed to satisfy different load requirements?
The ‘Hallen Derrick’ has a similar concept to the ‘Velle’, in that the topping lift arrangement and the slewing wires are incorporated together and secured aloft, clear of the lower deck. The outreach and slew are wide achieved by the ‘T’ yoke on the Velle Derrick and by outriggers with the Hallen.
Both systems are labour saving and can be operated by a single controller, operating the luffing and slewing movement together with the cargo hoist movement.
The Hallen is distinctive by the ‘Y’ mast structure that provides the anchor points for the wide leads. The derrick also accommodates a centre lead sheave to direct the hoist wire to the relevant winch.
Cranes Vs Derricks
