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 MIL-HDBK-1038
cranes are not equipped with any of these devices, and when they are to be
retrofitted with them, a Crane Alteration Request must be submitted to the NCC for
approval.
4.5.29.1 Load Indicating Devices. LIDs are required on all cranes in longshoring
service; the weight of the load under the hook must be displayed in the operator's
cab. Alternatively a device which would prevent an overload condition could be
used. LIDs are intended to verify the weight of the load being lifted after its
weight has been closely estimated by other means; they are not to be used as
"short cuts" to load estimation. LIDs are appropriate on straight-line rated boom
cranes and other crane types not subject to overturning. The load determination
is either direct (measurement of the wire rope tension at a fixed dead end) or
indirect (measurement of the lateral deflection force of wire rope between three
sheaves in a rigid frame). Direct reading LIDs may be wired to the control and
display circuits or they may send a radio frequency signal to system receivers.
Indirect reading LIDs are usually wired to the control and display circuits. LID
installations have provisions to account for the number of parts of line in the
reeving system. Retrofitting of LIDs is at the discretion of the local activity.
Portable battery powered LIDs, intended for suspension from the crane
load hook, are also available. They have an eye or shackle at the top to engage
the crane load hook and a shackle or their own load hook on the bottom for
connection to the rigging. The weight of the lifted load is sensed directly and
displayed on the side of the LID frame. Additionally, these LIDs include an
option for radio transmission of the lifted weight to a remote mobile or built-in
receiver in the operator's cab. The remote receivers may be obtained with
integral visual and audible alarms to signal overloads.
The Recommended Practice of SAE Standard J376, Load Indicating Devices in
Lifting Crane Service, establishes the minimum performance criteria for the
measurement and display systems of LIDs.
4.5.29.2 Load-Moment Indicating Systems. LMIs are required to be provided on all
new mobile cranes. Use of an LMI would meet the requirement for a LID on a crane
in longshoring service. They utilize a processor to combine the output of a LID
with boom angle sensors to monitor and restrict crane operation to its approved
strength and stability limits, as defined by the particular crane's load chart.
LMIs provide a continuous visual display of the margin of stability for the lifted
load at the particular radius as the load is maneuvered, and can be programmed to
warn the operator with an audible or visual alarm or to automatically stop the
motion in the outward or less stable rotational direction. However, LMIs do not
take into consideration the effects of wind or slope, and the crane operator must
be judicious on reliance on these devices.
The Recommended Practice of SAE Standard J159, Load Moment Systems,
establishes the minimum performance criteria for these systems. Additional
requirements of OSHA Regulation 1917.46, Load Indicating Devices, apply to cranes
used in longshoring service.
4.5.29.3 Anti-Two-Block Devices. A2Bs are intended to prevent the lower block
from being hoisted into the structure of the crane. Navy boom cranes have
traditionally incorporated limit switch arrangements to preclude two-blocking.
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