Multipurpose hybrid field support vessel of note

30 Jan 2017

'Harvey Stone' demonstrates its fire-fighting capabilities (RAL)

'Harvey Stone' demonstrates its fire-fighting capabilities (RAL)

Field support vessels with European involvement have been featured of late, a recent US-based delivery is worthy of note however in an area providing opportunities for providers of specialist bespoke towing vessels.

At a depth of 2,900m, Shell’s Stones oil and gas project in the Gulf of Mexico is the world’s deepest such facility, production carried out via an FPSO. Such installations are in effect fixed and therefore dependent on support from associated vessels. The field support vessel Harvey Stone is now in service with Shell having been completed by Eastern Shipbuilding Group Inc for client Harvey Gulf International Marine LLC.

Harvey Stone fulfils a demanding role providing towing support for both day-to-day and emergency situations. The vessel is a Robert Allan Ltd RAmpage 6400 design, the largest in the series and first such with a sponsoned hull form. Its primary duty is as dedicated pull-back tug assisting in berthing, loading and unberthing offtake tankers up to 46,287dwt in winds up 15m/sec and 2.5m significant wave heights for berthing operations and winds up to 20m/sec with 3m wave heights for pull-back operations.

It is also required to escort, and in emergency tow the FPSO in the event of disconnection from its submerged buoy mooring during hurricane avoidance procedures. It provides evacuation assistance in line with the Gulf of Mexico Emergency Evacuation Plan including capacity for 120 survivors. Additional duties include inspection and maintenance of the floating hose, transportation of bulk, liquid and containerised stores to the FPSO and it is also capable of anchor-handling duties. The vessel meets DP2 standards to assist with the above demands.

Main particulars include: LOA 64.8m, beam 18m, maximum draught 6.4m, fuel oil capacity 874m3, fresh water 192m3, foam 94m3 and ballast/drill water 1,496m3. Harvey Stone follows recent trends when determining the machinery installation in adapting the arrangement to suit the operating profile. As with ship-handling tugs in ports, it spends a large percentage of its time in loitering mode but must produce a respectable 106tbp when operating in tow-assist mode.

To allow an economical solution along with due regard to environmental sensitivities, a hybrid propulsion arrangement was chosen. The installation allows for economic propulsion (eco-transit) at eight to nine knots and station-keeping on one engine mechanically/electrically connected to propulsion units and/or bow thrusters. The system has a dual output single input gearbox driving the propulsion shaft line on one side and the motor/generator on the other. This arrangement allows all propulsion units plus the ship’s load to be run off one main engine and is configured to operate with electrical power generated with shaft alternators in conventional or DP mode.

The machinery installation itself consists of two GE 12V250 MDC main engines complying with EPA Tier 4 emissions requirements. Each engine is rated 3,495kW at 1,000rpm driving Schottel SRP 3030CP azimuth thrusters with 3,400mm CP propellers via a Reintjes LAF 3414 gearbox. Performance figures are 106tbp and top speed of 13kn minimum. Two Schottel STT2 610kW tunnel thrusters aid manoeuvrability including in DP mode. The ship’s electrical power generation and hybrid system is provided by Robichaux Automation and Control Inc. Auxiliary machinery includes two Cummins QSK19 350ekW gensets, two Marelli shaft motor/generators and finally a Cummins QSB7 120ekW emergency genset. FFS provides the off-ship firefighting system to FFV2 class notation.

Harvey Stone is well equipped for towing with a single-drum hawser winch forward and a waterfall, double-drum towing winch aft. Other deck equipment includes: stern roller, shark’s jaw top pin unit, gobeye, deck crane, tow hook, tugger winches, capstans and storage reels.

Normal operating crew for the ABS-classed vessel is 15 with provision for a total of 24 persons and special attention was paid by Eastern Shipbuilding to meet HAB+ noise and vibration requirements including vibration isolation of main engines and silencers. To ensure these standards were met the builders commissioned a separate noise study, including an FEA model of the hull by Noise Control Engineering.

By Peter Barker

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