A ferry good idea

Amidst much public concern about the overall safety of roll-on roll-off ferries and equipment, a dynamic, independent braking device has been jointly developed by Bosch Rexroth and design consultant Royal Haskoning.

Intended for incorporating into new linkspan and walkway designs or retrofitting to existing installations, the self-contained Rosafe will instantly initiate an emergency braking operation arresting the bridge’s fall in around 1/10th of a second or 300mm, without inducing excessive loads. It enables continued use of the linkspan or walkway for a period after failure and provides the means of supporting the equipment in a normal parked or maintenance position, replacing or upgrading a separate sprigging system.

The majority of linkspans and walkways are operated by hydraulically or winch operated lifting-type equipment. Although generally fairly reliable, these systems do suffer a significant number of minor operational problems, and the new development comes as the industry as a whole is reviewing the design and operation of the equipment.

After considering a number of options including duplicate cylinders or winches and walking or spragging support systems, the two companies concluded that an independent safety device was the best solution.

They wanted something that was failsafe, could immediately arrest uncontrolled movement and would be truly independent of the main control system, employing different technology to prevent common mode failure.

The Rosafe, essentially a hydraulically operated linear brake running on its own supporting rod, consists of a spring-applied cone brake assembly, which is hydraulically released and floats within a sealed chamber. The chamber itself is pressurised with hydraulic fluid to absorb the dynamic forces derived from emergency operation.

The body is gimbal mounted to the main lifting structure and guide bearings at the top and bottom enable free movement up and down the rod.

With its own self-contained hydraulic power pack, the Rosafe would normally be installed in pairs. It follows the routine movement of the lifting equipment, but as soon as its sensors detect abnormal downward movement the brake is operated.

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