Rock Discharge System

Handling XXL rocks at sea

Subsea rock installation is necessary for scour protection and for the protection of subsea cables and pipelines. Van Oord’s latest innovation for installing a wide range of rock sizes is the Braveness, a flexible fall pipe vessel used for subsea rock installation. Rock is loaded onto the Braveness at a quarry. The rock is stored in the Braveness in two cargo holds with a total storage capacity of 15.500 ton. The rock can be discharged with pinpoint accuracy from the vessel onto the seabed in three configurations. First by discharging the rock through a fall pipe through the moonpool. Secondly, by discharging over the side of the vessel through the fall pipe, and third by discharging over the side of the vessel using a tremie pipe.

Van Oord commissioned TME to design and construct the rock transporting system for the Braveness. Two heavy-duty hydraulically driven longitudinal apron plate feeders transport the rocks from the two cargo holds into the moonpool chute and into the fallpipe. The apron plate feeders are fed by vibration feeders for the lighter rocks. Heavy rocks are picked up by an excavator fitted with a grab and loaded into a hopper which is integrated in the side skirts of the longitudinal apron plate feeders.

For discharging over the side of the vessel, the rocks are transported to the side of the vessel by a transverse apron feeder. This apron feeder is equipped with a dedicated chute depending on whether rocks are discharged via the tremie pipe or fall pipe.

The rock transporting system is designed to carry extreme loads and endure heavy wear. Extra thickness, wear resistant materials, exchangeable parts and many other measures have been taken to ensure a functional system with an appropriate lifespan.

Key facts & figures

Scope of workConcept design, detailed engineering, production drawings, fabrication, project management
Number of apron feeders3
Dimensions apron feeders30m x 2m (longitudinal conveyors) ∣ 16,5m x 2m (transverse conveyor)
Deadweight180 tonnes (2 x longitudinal conveyors) ∣ 90 tonnes (transverse conveyor)
Loading capacity12.000 tonnes
Discharge capacity2.000 tonnes/hour