TM 55-1930-203-10
Section IV. Maintenance Procedures
3-7. Electrical System
a.
Description. The LARC is equipped with a waterproof, 24-volt electrical system (two 12-volt batteries in series), which
provides power for the electrical system and communications. Multiple conductor cables are used whenever possible.
(1) LARC illumination. Cargo well lights, controlled from the cab, provide general illumination in the cargo area. There
are four headlights: two port and two starboard. A 24-volt searchlight, with 360 horizontal rotation and vertical adjustment is
mounted on the top of the cab and is operated from inside the cab. This light provides lighting at any point on the deck or cargo well
or for general illumination. The navigational lights include one range light mounted on a 20-inch staff on top of the cab at the aft
inboard corner, one bow light (clear) mounted on the top of the cab at the forward inboard corner, and two running lights mounted on
the bulwark forward end. The green running light is on the starboard side and the red running light is on the port side. Ultraviolet
black lights provide illumination for the instrument panel in the cab. The trouble and signal lights, one mounted on the interior
starboard cab bulkhead, and the other in the forward starboard compartment beneath the scuttle, have a 24volt sealed beam lamp
mounted on a pistol grip handle attached to a cable with a self-winding reel. Each light assembly is controlled by a trigger switch.
(2) Switches and receptacles. The machinery space lights are controlled by two switches near the access ladder, port
and starboard. One switch controls the lights on the upper level and the other switch controls the lower level. The wing compartment
lights are controlled by switches at the light fixtures. Two mechanic's lights, each with a 35-foot extension cord, are provided.
Receptacles for these are installed in the wing compartments. Two additional receptacles are installed for devices in' the machinery
space, one port and one starboard. These receptacles are energized at all times.
(3) Warning lights. A master warning light and individual warning lights are installed in the cab. In general, the following
alarms, connected with the master and other warning lights provide the operator a warning of improper fluid level, pressure or
temperature in the propulsion system:
(a) Low engine oil pressure.
(b) Low hydraulic oil level.
(c) High engine water temperature.
(d) High transmission oil temperature.
(e) Low transmission oil pressure.
(f) Low gathering box pressure 0 (this warning light no longer used).
(g) High gathering box temperature.
(h) Low marine gear pressure.
(i) High marine gear oil temperatures.
(4) Circuit breakers. A circuit breaker panel in the cab provides overload protection for the warning lights, headlights,
navigation lights, master switch control circuit, search and trouble lights, compartment lights, heat and ventilation, and cargo lights.
(5) Generators and voltage regulators. Two generators are installed, one in each machinery compartment, and are belt
driven from the output shaft of the gathering boxes. A voltage regulator controls each alternator. All electric cables are identified with
metal tags.
b.
Maintenance. Operator personnel are not authorized to perform maintenance functions on the electrical system. Report
all defects to organizational maintenance.
3-8. Hull Components (fig. 3-13)
a.
Description.
(1) Cab. The cab is constructed of welded steel with glass windows all around. It is located on the port deck aft and
seats three crew members. There is a sliding steel hatch on the top over the operator's seat, and a steel weathertight hinged door on
the inboard side of the cab. On LARC's 19 through 60 the sliding hatch has been replaced with a scuttle cover. Controls to be used
by the operator are concentrated in the cab. The upper part of the cab is removable so that the overall height of the cab can be
reduced by approximately 3 feet 9 inches. When the top of the cab is removed, the searchlight and radio antenna are also removed.
(2)
Access hatches and plates.
WARNING
Personnel will never enter machinery compartment without being constantly
under observation by a second individual because of the danger from fumes.
The ten engine space hatch covers are equipped with latches and are sealed by rubber gaskets. Spun aluminum scuttles are
provided for access to compartments not having hatches, but having machinery or equipment requiring regular ser-
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