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Hydraulics help ferry passengers to board safely
Published:  01 November, 2003

Hydraulics help ferry passengers to board safely

In September 1994, six ferry passengers were killed and seven were seriously injured when a pedestrian walkway collapsed at the port of Ramsgate, Kent, in the UK. The accident brought home the dangers posed by these walkways which have to cope with the effects of the tides, waves and impacts by ships.

Canada`s national standards body has recently issued a standard calling for a second, independent connection to support these ramps if the primary system fails. In response to this document, the Royal Haskoning engineering consultancy has been working with Rexroth Industrial Hydraulics in the UK to develop an emergency braking system that operates in parallel with the existing lifting equipment to support a walkway or vehicle bridge if the main equipment fails.

The system, called RoSafe, could be used on new walkways and linkspans, or retrofitted to existing installations. It consists, essentially, of a hydraulically-operated linear brake running on its own support rod. Normally, this follows the movement of the main lifting equipment, but if an abnormal downward movement occurs, the system initiates a braking action that will stop a load of up to 500 tonnes within tenths of a second and 300mm of travel.

The device consists of a cone or collet brake assembly which is released hydraulically and floats in a sealed chamber, pressurised with hydraulic fluid to absorb the dynamic forces generated during emergency operations. It is gimbal-mounted to the main structure and guide bearings allow the cylindrical rod to move up and down. The rod incorporates an accurate CIMS measuring system for precise positioning.

The RoSafe devices are designed to be installed either singly or in pairs and are available in capacities from 50-500 tonnes. Rexroth says that the system is a cost-effective alternative to installing duplicate lifting equipment.

For example, a conventional four-cylinder lifting system for a 300-tonne, single-ramp linkspan, costs around £250,000. A two-cylinder system used with two RoSafe devices would add about £25,000 to this, but would provide full redundancy and safe ship loading without needing mechanical spragging. If Rosafe was incorporated into the cylinder bodies of a conventional two-cylinder installation, there would be a 20-30% cost saving compared to a conventional four-cylinder system, Rexroth estimates.

The RoSafe development programme has been overseen by the German technical inspection body, T‹V. The first production prototypes are being assessed by Lloyds, the HSE and BSI consultants.

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