Pump Apparatus and Underwater Trenching Apparatus

An underwater trenching apparatus for operation in shallow water, the apparatus comprising a trench-cutting high pressure jetting tool and a primary pump having a relatively high pressure fluid output in fluid communication with said jetting tool and a relatively low pressure fluid input, and means, associated with said primary pump fluid input, operable where the ambient pressure is insufficient to prevent cavitation in the primary pump, to locally increase the pressure at said primary pump fluid input.

A method of operating an underwater trenching apparatus for operation in shallow water, the apparatus comprising a trench-cutting high pressure jetting tool and a primary pump having a relatively high pressure fluid output in fluid communication with said jetting tool and a relatively low pressure fluid input, the method comprising, where the ambient pressure is insufficient substantially to prevent cavitation in the primary pump, locally increasing the pressure at said primary pump fluid input.