US Navy divers recently completed a first-time full underwater waterjet seal on the Littoral Combat Ship (LCS) USS Fort Worth which enabled them to inspect and replace the cathodic protection system anodes mounted in the intakes. On this waterjet propelled ship it’s a job that needs to be done every four months, and so NAVSEA’s Supervisor of Salvage and Diving (SUPSALV) was tasked to develop a procedure that would enable the anodes to be replaced at sea in order to avoid dry-docking.
A3 Series Waterjet: Rendering courtesy of Rolls-Royce
In early course Navy engineers developed a plate to seal the waterjet inlet, as well as external patches to isolate the waterjet, so as to create a dry working environment for the inspection (a fairly common procedure in smaller waterjet propelled vessels for this kind of inspection, but less so for a large warship of this type). Joe Theodorou, SUPSALV program manager pointed out: “Having this capability saves the Navy $100 million in dry dock costs in the San Diego area."
USS Fort Worth: Power & Propulsion
The 387-foot long Fort Worth is the third LCS (multi-purpose-module, hi-speed shallow-draft warship) delivered to the Navy. She is the second of the semi-planing monohull ‘Freedom’ variants (as opposed to the trimaran ‘Independence’ variant) and was constructed in the Marinette Marine shipyard.
LCS 'USS Fort Worth':Photo courtesy of Rolls-Royce
The warship is powered by two Rolls-Royce MT30 36MW gas turbines and two Fairbanks Morse Colt-Pielstick 16PA6B STC diesel engines driving four large, acoustically optimised Rolls-Royce waterjets which give the LCS a speed of +40 knots. In addition, four Isotta Fraschini Model V1708 ship service diesel generators meet high demands for auxiliary power.
The MT30 gas turbine is derived from Rolls-Royce aero engine technology and according to them, builds on over 45 million hours of operating experience. At 36 megawatts, it is the world’s most powerful marine gas turbine and has the highest power density in its class.
The waterjets are among the largest produced by Rolls-Royce, who say that these Axial Mk1 waterjets are very power dense, delivering more cavitation-free performance for their size and power than any other waterjet. The ‘Wow’ factor is that at 22MW of power, a single waterjet of this scale can move almost half-a-million gallons of seawater per minute.