The NATO Improved Ribbon Bridge Family ~ Part 2

The Improved Ribbon Bridge family of modular flotation bridge systems is a NATO wet-gap crossing asset evolved from a 1960s Soviet design, continues Carl Schulze.

The Ramp Bay and Interior Bay of the Improved Ribbon Bridge (IRB), or Faltschwimmbrücke Typ 2 (FSB2) in German service, are floating integral superstructures made of aluminium that function as pontoons and feature a roadway surface.

The Interior Bay is a four-pontoon folding module consisting of two inner and two outer pontoons; each inner pontoon being divided into two watertight compartments. The Interior Bay unfolds automatically once released and afloat. The bays are connected to each other by first manually engaging four upper couplings, followed by two lockpins on the inner pontoons. The lockpins act as bearing points between consecutively joined bays, thus allowing the entire bridge to hinge with the weight of a moving vehicle and/or uneven water conditions.

The Ramp Bay is also a four-pontoon module and functions similar to the Interior Bay, but differs substantially in design. The ramp end of the inner pontoons of the Ramp Bay extends lengthwise, beyond the outer pontoons and slopes down, forming the ramp edge. The sides of the outer pontoons are slightly tapered toward the ramp end and attaching ramp plates are provided. The Ramp Bay contains a manually controlled raising mechanism that is utilised when joined to an Interior Bay. The angle or height of this can be adjusted to meet various bank conditions. The Ramp Bay also contains two lockable, self-draining stowage boxes recessed in the outer pontoons.

According to the US Army technical manual TM 5-5420-278-24&P Unit, Direct Support and General Support Maintenance Manual for Improved Ribbon Bridge, the bays feature the following designations: M16 Ramp Bay (NSN 5420-01-470-5825) and M17 Interior Bay (NSN 5420-01-470-5824)

Ferries and bridges are usually built with the SRB, IRB and FSB 2 in the same way and in the following this procedure is only briefly described. After a possible bridging or ferry site has been identified, first the Bridge Erection Boats (BEB) are launched in the same way as later on the bridge bays.

First the boat crew and a bridge erection team climbs aboard, then the bridge transporter carrying the boat reverses down the riverbank into the water. The boat is then launched, either by gravity or with support of the truck mounted hydraulic boom in the case that the gradient of the river bank is not steep enough. Once at the critical angle, the boat slides down over rollers into the water. With enough BEBs for the planned bridge or ferry deployed the bridge bays are then launched.

When launched the bridge bays are still folded, on hitting the water its pressure and the hinging arrangement of the bridge bay automatically ensure their opening. Once afloat, a BEB will now take care of the launched bridge bay and engineers climb onto the bay and lock the two centre pontoons and two side pontoons in place.

In the next step individual bridge bays are manoeuvred next to each other with the BEBs and are then coupled together, for example to form a four bay ferry consisting of two interior bays and two ramp bays, or a bridge section consisting of a ramp bay and several interior bays. Connecting of one bay to another takes about one minute. If bays of the Improved Ribbon Bridge (IRB) are used in conjunction with bays of the older Improved Float Bridge (IFB) connecting them will take about two minutes.

In the case of a bridge, rather than a ferry, several bridge sections are navigated into place by the BEBs and then coupled together to complete the bridge. Finally the bridge is anchored to the shore with cables and the ramps of the ramp bays are adjusted to the shore gradient. Attached to the interior bays, the BEBs are now used to keep the bridge in place, basically compensating for the current. During a ferry service the BEBs are used to power the ferries and to navigate them to the assigned landing points. According to GDELS skilled personnel can erect a 100m long IRB or FSB 2 bridge in approximately 30 minutes under favorable conditions.

Technical Data FSB 2 and IRB*

• Interior bay total length: 6.92m
• Interior bay width folded: 3.3m
• Interior bay width unfolded: 8.63m
• Interior bay height folded: 2.35m
• Interior bay height unfolded: 1.3m
• Interior bay total weight: 6.350kg
• Ramp bay total length: 6.92m
• Ramp bay width folded: 3.19m
• Ramp bay width unfolded: 8.63m
• Ramp bay height folded: 2.35m
• Ramp bay height unfolded: 1.3m
• Ramp bay total weight: 6,350kg
• Payload ferry and bridge operation – single load: Tracked vehicles up to MLC 80 and wheeled vehicles up to MLC 96
• Usable deck width ferry and bridge operation, single lane loading MLC 80/MLC 96: 4.5m
• Usable deck width ferry and bridge operation, two lane loading MLC 20 tracked/MLC 14 wheeled: 6.75m
• Bridge bays required for a 100m long bridge: 13x Interior bays and 2x Ramp Bays
• Construction time for a 100m long bridge: approximately 30 minutes.

*Figures from a GDELS product brochure

{ images © Carl Schulze unless noted }