01 Dec 2004
Rosafe was developed by Posford Haskoning and Bosch Rexroth in the UK

Rosafe was developed by Posford Haskoning and Bosch Rexroth in the UK

As highlighted above, although accidents have been relatively rare, passenger safety is of interest to everyone in the industry, and, with this in mind, a new safety device for ferry linkspans has been produced jointly by Royal Haskoning and Bosch Rexroth.

The new device, named RoSafe, is a secondary system that works independently of the operating mechanism that moves a linkspan or walkway into position. It acts as an independent brake should the lifting mechanism or the structure fail.

RoSafe is based on static brake technology commonly used on heavyduty presses, lifts and the like, but adapted for dynamic braking. After successful testing, the brake is now available for new builds and retrofit on existing structures requiring braking capacities of up to 1,000 tonnes (using two RoSafe units).

The brake is installed in a cylinder incorporating within it an independent piston rod. The rod is allowed to move freely within the brake until there's an emergency.

When there is sudden downward movement, sensors detect this abnormal circumstance and apply the brake immediately. Damping minimises shock loads appropriate to the strength of the structure.

Importantly, the brake can also be used to lock/sprag a linkspan into any position, for example when extended maintenance work on the structure is needed.

Marks explains that the device meets the criteria of recent standards for linkspan and walkway safety: "Canada established a safety standard in 2001 for an independent secondary physical connection and BS 6349 Part 8 includes a similar requirement, subject to consultation."

He believes RoSafe is the only purpose-built component to be designated a 'Safety Machine' in accordance with the requirements of the Machinery Directive. "We expect to see the device used in preference to the doubling-up of cylinders, winches and the like. RoSafe is able to match or better the safety performance of these methods, fully satisfying the requirements of legislation. It also does so in a much more cost-effective way, so we believe it offers great advantages to port operators."

Normally installed in pairs, or singly on lighter walkways with sufficient torsional stiffness, the RoSafe follows routine movement of the main lifting equipment in either direction, but if abnormal downward movement is detected, the braking action is initiated within milliseconds. When movement has ceased, RoSafe can then be returned to the pre-fall position, while maintaining 'brake on' status. It can also be activated routinely for supporting the ramp in the parking/ maintenance position, acting as a spragging device; the linkspan can be supported at any position, giving the further advantage of flexible spragging.

A lifting system for a typical 300 tonne, single ramp linkspan, with a four cylinder system (two per side) including hydraulic power unit, electrical control system and installation, would cost around £250,000. A similar two cylinder system, incorporating two RoSafe devices (one cylinder plus one RoSafe per side) would cost around £275,000, but would bring additional benefits of 100% full redundancy and live safe loading of the ship, without the requirement for mechanical spragging.

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