US Navy get their first new ‘Z-Tech’ tug - by Jack Gaston
The first of a series of four new Z-Tech 4500 class tugshas entered service with the United States Navy Pilots operating in Puget Sound, Washington state, USA.
Named YT 802 Valiant, the tug was handed over to its owners in late December 2009 and started work in earnest in February after a shakedown period and crew training.
In spite of its familiar YTB designation, Valiant is quite different to any of its predecessors used to attend naval shipping in the area. The design by Robert Allan Ltd of Vancouver is based on the widely accepted Z-Tech 6000 hull form originally developed for the Port of Singapore and adapted to meet the specific needs of the Navy Pilots.
All four tugs are being built in Tacoma, Washington by JM Martinac Shipbuilding Ltd, a sub-contractor to Pacific Tugboat Services of Long Beach, CA, the prime contractor for the delivery of the vessels to the Navy. The tugs will be based in Bremerton and Bangor, Washington, to perform shiphandling duties for the full range of US Navy surface warships and submarines.
The Z-Tech 4500 class tugs are 27.42m in length overall, with a beam (moulded) of11.65m, a depth of 5.00m and a minimum loaded draft of 4.88m. A pair of Caterpillar 3512C main engines generate a total of 3,620bhp (2,700 kW) at 1,600 rpm, to drive Schottel Model SRP1012 fully steerable propulsion units with 2,100 mm diameter fixed pitch propellers. On trials this combination delivered a bollard pull of 42 tons (92,500lbs) towing ahead and 45 tons (99,205lbs) astern and a free running speed of 12.4 knots, exceeding the predicted performance.
Electrical power is supplied by a pair of auxiliary generators by RA Mitchell, each powered by a John Deere 6068SFM75 engine and rated at 130ekW at 1,800 rpm.
Deck machinery fitted includes a JonRie Series 210 shiphandling towing winch forward carrying 180m of 175mm (circumference) towline. The winch has a brake capacity of 136 tons (300,000 lbs), and a line pull of 9 tons (20,000 lbs) at 53 m/min.
In order to work safely with both surface warships and submarines, the tugs are equipped with an extensive array of fendering above and below the waterline. The fendering is all rated ‘non-marking’ to deal with the grey hulls of warships and is a Shibata product supplied through Schuyler Fenders.
The tugs are configured as ‘day-boats’ but also have accommodation for a crew of up to six persons. One of the unique features of the layout is the complete separation of the accommodation deckhouse from the machinery casing, a configuration designed to both provide a reasonably dry access to the accommodation spaces in the notoriously damp Pacific northwest climate, and to provide a significant degree of noise attenuation in the crew spaces.
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