Page 200 - Introduction to Marine Engineering
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Deck machinery and hull equipment 185
Outboard
derrick
Cargo hook
over quay
Figure 10.3 Union purchase rig
Figure 10.4 General cargo crane
Cranes have replaced derricks on many modern ships. Positioned
between the holds, often on a platform which can be rotated through
360°, the deck crane provides an immediately operational unit requiring
only one man to operate it. Double gearing is a feature of most designs,
providing a higher speed at lighter loads. Various types of crane exist
for particular duties, for example a general duties crane using a hook
and a grabbing crane for use with bulk cargoes.
A general cargo crane is shown in Figure 10.4. Three separate drives
provide the principal movements: a hoisting motor for lifting the load, a
