Necessity is the mother of Mini Dredge

The Cheetah Mini Dredge was launched in February and following a series of successful trials is undergoing the final stages of build to maximize its efficiency as a small suction dredger.

Sediment and seaweed at Ventnor Haven have been a serious problem since the Haven was constructed in 2003. Sand and seaweed are continuously carried into the haven in suspension, especially during periods of rough weather. Once trapped within the Haven the seaweed breaks down anaerobically, producing noxious fumes, including hydrogen sulphide based compounds known to be dangerous to health. The sand accumulates within the entrance, forming a sand bar which reduces the time frame during which the Haven can be accessed by the local fishing fleet.

The Cheetah Mini Dredge is an open boat adapted from the builder’s 10.2m catamaran design. The bow features an aluminium A frame with track sliding which guides the pump head vertically into the water column through Cheetah’s 1m² moonpool. Unlike conventional dredgers, the sliding nylon 5” pipes prevent the pumphead from straying horizontally as the boat is manoeuvred.

Sean Strevens, Cheetah designer and now dredge tester said, “Initial trials have delivered very satisfactory results. We are aiming to clear the Haven of the previous year’s weed so that we can tackle the 2012 influx in late spring as and when it arrives. This will avoid the ensuing decomposition and associated bad smells which have affected trade to the town and esplanade over previous years. Last year we cleared the Haven over a four week period using diggers and dumper trucks. By regularly operating the pump we should be able to keep on top of the problem and avoid any inevitable disruptions caused by heavy machinery operating along the Eastern Esplanade.”

The power pack and dredge pump is manufactured by Dragflow and consists of a 170 hp six cylinder diesel hydraulic power pack driving a Dragflow HY85 dredge pump with a maximum capacity of 200 m³ per hour.

The total weight of the unit is three tonnes, for a combined weight of six tonnes including the vessel. A Spencer Carter hydraulic cargo winch is mounted on the bow which lifts the pump head from its extended position at 2m below the keels to the deck. The pump can be operated at any position from a minimum of 0.4m to 2m maximum draft.

Sea trials have proved most efficient at an engine speed of 1,000 to 1,200 rpm, which pumps at a capacity of 150m³ per hour and a 50% solid to water ratio. The pump is connected to a 6” heavy duty discharge pipe with Bauer fittings. Discharge is directly over the haven southern rock arm. The material, already in solution, is then dispersed by the tide.