What is a raft bridge?
A raft bridge is a floating bridge in which the deck rests on a raft. It resembles a pontoon bridge, but instead of separate floating boxes (pontoons), a raft forms the floating body. In Dutch it is called a vlotbrug; in English the general term is floating bridge.
How it works
The raft carries the deck and rises and falls with the water level. On each bank there is often a fixed bridge section that extends some way into the water; the raft spans the gap in between. Many raft bridges are movable: to let a ship through, the connection is released and the raft is pulled aside or under a fixed section. Afterwards it is pulled back and secured.
A well-known Dutch example was the raft bridge over the Noordhollandsch Kanaal at Koedijk, made with two long rafts between two fixed bridge sections.
Applications
Raft bridges were mainly used over canals and waterways where a fixed bridge was too expensive or would hinder shipping, and where the water level is fairly constant. Today you still see floating bridges for pedestrians, in nature areas, at marinas and as temporary river crossings.
Points of attention
- Load capacity: the permitted load depends on the buoyancy of the raft. Overloading makes the bridge tilt or sink too deep.
- Changing water levels: the connection to the bank must accommodate height differences, for example with a hinged approach ramp.
- Maintenance: timber rafts rot and floats can start to leak. Regular inspection is needed.
- Current and wind: anchoring and guides keep the bridge in place.
Related terms
- Pontoon bridge
- Swing bridge
- Drawbridge
- Bascule bridge
- Beam bridge
- Abutment
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