VT4 Scour Protection
Stena commissioned the development of the VT4 berths in Belfast Harbour to minimise the transit times of their ferries to the open water of Belfast Lough. The development consisted of 2 berths for their conventional Ro-Ro ferries and a custom fendered berth with link span for their high speed HSS ferry.
The HSS is propelled by two large high capacity water jets which coupled with the soft mobile nature of the seabed in Belfast lough meant that there was an extreme danger of the water jets scouring out the toe of the newly constructed steel pile combi wall.
Norfolk Marine were contracted to install the constant thickness fabric formwork scour mattress on the dredged sea bed and fill it with micro-concrete using a subcontract boom pump supplied by the main contractor. Pre installation surveys of the dredged bed and post installation surveys of the mattress were carried out using by Norfolk Marines dive team using acoustic positioning equipment. The total area of installed mattresses was 90 x 30m.