DESCRIPTION AND THEORY OF OPERATION
IMPROVED RIBBON BRIDGE (IRB)
RAMP BAY M16
NSN 5420-01-470-5825 P/N 12478918;
INTERIOR BAY M17
NSN 5420-01-470-5824 P/N 12478919.
Section II. THEORY OF OPERATION
GENERAL
This section explains how components of the IRB-I, IRB-R, CBT, and BAP work.
A functional description of the IRB, CBT, and BAP components and their operation
are covered in the following paragraphs.
HOW THE BAY UNFOLDS/FOLDS
Unfolding and folding operations involve the action of the bay’s two inner and
outer pontons and the cables, levers, and springs or torsion bars that make up the
unfolding/folding mechanism. Once the bay is launched, the actual movement or
unfolding is caused by the forces of gravity and buoyancy generated as the bay is
released and begins to float. The unfolding mechanism’s function is to assist and
dampen the movement of the pontons about their hinged joints. The unfolding of
the bay is automatic, whereas, to fold the bay it must be lifted from the end at the
center. The lifting force (provided by the transporter) causes the inner pontons to
move about their hinged joints, and their movement forces the unfolding/folding
mechanism’s cables, levers, and springs (IRB-I) or torsion bars (IRB-R) to
simultaneously pull the outer pontons up, about their hinged joints, thus folding
the bay.
FUNCTION OF THE PONTON LOCKS
The ponton locks are designed to hold the bay in the folded or unfolded position.
When an IRB-R or IRB-I is placed in the folded position its inner and outer pontons
are held by foldlocks and travel latches. These locks are manually engaged or
disengaged during a controlled launch, retrieval, transport, and ground storage of
the bay, but are not engaged when the bay will be used in the unfolded position. To
secure the IRB-R or IRB-I in the unfolded position, the bay’s inner pontons are
locked by two manually engaged transverse couplings. The bay’s outer pontons are
then secured by manually engaging four swivel hooks on the IRB-R or four outer
ponton locks on the IRB-I. Once secured in the unfolded position, the bay is ready
for bridge or raft construction.
TM 5-5420-278-10
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