The rotate drive and the rotate bearing designs must consider
rotation out of the horizontal plane due to the list and trim of the barge.
The diesel engine-generator set and fuel tank may be located in the
barge, rather than the machinery house.
Hydrostatic drives are the norm on modern cranes.
e) Tie down and locking provisions for the boom and upperworks are
required for towing in the open seas.
Distinctive Features. Since it is desirable to maintain a low center of
gravity for stability in the water, the elevation of the machinery deck is
restricted. Compared to portal cranes, all portions of floating cranes are at a
low elevation. To mitigate this condition, the boom hinge pin and operator's cab,
are often raised above the roof level of the machinery house. The rated
capacities and reaches range up to 115 tons at 80 feet, respectively. The booms
frequently have a long extension in the form of a jib to increase the reach of the
whip hook for servicing masts and periscopes of Navy vessels.
A conspicuous boom rest is located at the bow end to support the boom
when the crane is not operating and to secure it for towing. A pilothouse is
sometimes installed at the bow, often within the boom rest.
Industry Standards. The design of barges is regulated by Rules for
Building and Classing Steel Barges, published by the American Bureau of Shipping.
The barge design includes the reinforced circular column (tub) which supports the
roller path or the rotate bearing of the floating crane upperworks. Structurally
these cranes are designed in compliance with the applicable requirements of the
Manual of Steel Construction, published by the American Institute of Steel
API Specification 2C, Specification for Offshore Cranes, published by the
American Petroleum Institute, prescribes a method for calculation of loads on the
ASME B30.8, Floating Cranes and Floating Derricks, published by the
American Society of Mechanical Engineers. This standard focuses primarily on the
safety aspects of the design and operation of these cranes.
Various U.S. Coast Guard regulations impose seaworthiness, safety, and
human occupancy requirements.
Container Cranes. Container cranes are optimized for rapid loading and
off-loading of standard shipping containers. The containers are transferred
between the container ship and the dock storage area or the truck carriers. The
crane rails are straight and the waterside rail is located close to the edge of
the wharf or pier. Container cranes in commercial service are often shore-
powered, with the electric power cable spooled on a reel and laid in a trough
running parallel to the land side rail; those in Navy service are self-powered
with an on-board diesel engine-generator set. These cranes are equipped with
several standard lengths of frames (spreaders) to engage different sizes of
containers both above deck and inside the ship's holds. The standard maximum
weight of containers is either 40 or 50 long