New Navy tractors steal the show from traditional YTBs

Jun 7, 2010 12:00 AM

The great bulk of the 1,092-foot-long aircraft carrier John C. Stennis (CVN 74) loomed larger and larger as it advanced on the four tugs waiting at Restoration Point, in Washington’s Puget Sound. The February morning was clear, causing the U.S. Navy’s newest and most modern tug to stand out in the crisp air. This one had a distinctly different shape from the three traditional YTBs bobbing nearby in the light swell. The new tug, Valiant (YT 802), was in her first month of service.

New Navy ASD tug Valiant (YT 802) assists the carrier John C. Stennis into the Puget Sound Naval Shipyard with traditional Navy YTB Canonchet in background. (Brian Gauvin photos)
The Nimitz-class nuclear-powered carrier John C. Stennis was escorted by the four tugs through Rich Passage into Sinclair Inlet and finally into her berth in Bremerton, a distance of 10 miles taken at 10 knots. The critical juncture in the transit is a 95-degree bend at Point Glover, where Rich Pass meets Sinclair Inlet.

Valiant’s crew includes, left to right, Randy Garner, chief engineer, Randy Junell, chief mate, David Jones, captain, and Greg Bryan, deck hand.
“The pilots can’t see any water here,” said Capt. David Jones as he maintained Valiant’s position parallel with the carrier as it worked around the bend. “They have to take their position from houses on the point.”

Just before reaching the naval base, Valiant took up a position at the carrier’s bow, while YTB 823 Canonchet and YTB 812 Accomac, the two single screw tugs, lined up on the port side, and YTB 779 Manhattan, which was converted to a 4,000-hp ASD in 2006, took the stern.

Mate Randy Junall, and deck hand Greg Bryan, standing on the foredeck, by then cloaked in the shadow of the carrier’s flared bow, hooked the ship’s messenger line and tied on the tug’s seven-inch hawser. The tug has 600 feet of towing line wrapped on the JonRie InterTech 210 hawser winch, several feet of which were then winched up through the ship’s mooring chock. With the tugs in position, the pilot directed them through a 90-degree maneuver to swing the carrier into its berth.

Valiant is actually the first of four Z-Tech 4500-class ASD tugs designed for the Navy by Robert Allan Ltd., of Vancouver, B.C., and built by J.M. Martinac Shipbuilding Corp. of Tacoma, Wash. She, and others like her, are to be deployed at what the Navy calls Naval Region Northwest. They will be based at Bremerton, Bangor, or other Puget Sound Navy facilities. The second new Navy tug, YTB 803 Reliant, was delivered in May, with the last two tugs expected by the end of the year.

Valiant’s crew, including David Jones, captain, are civilian mariners hired by the Navy.
The foredeck of a Z-Tech tug, which is the winch end, with the pilothouse set back further than traditional tug designs, is the preferred working end of the tug. The set-back house configuration allows the tug to get in close under the flare of modern ships and carriers, and to tow astern, when necessary, in a true tractor style pull. The Z-Techs are designed to utilize the best operational characteristics of tractor-style tugs and ASD tugs, achieving close to omni-directional performance, as it applies to bollard pull and speed, traveling astern or forward. On trials, Valiant registered a bollard pull of 42 tons forward and 45 tons astern, a significant increase from her expected average pull number of 38 tons.

The relatively low bollard pull rating is reflective of the modest total of 3,620 hp derived from the Caterpillar engines — a power rating preferred by the Navy to ensure delicate handling of its submarines and ships, according to Jay Anderson, port captain for the northwest Navy region.

“We needed a tug that could handle the carriers, but also one to which we could apply a finer touch,” said Anderson. “We push the limits of the tug with the carriers, but we need to be able to fine tune our maneuvers for the smaller boats. So we didn’t want too much horsepower jerking us around.”

“We still got more bollard pull than we expected,” said Anderson. The bonus in bollard pull is attributed to the Z-Tech hull design, several of which, also built at Martinac, have shown the same increase in pulling power. “The boat is working very well for what it was designed to do and has outstanding creature comforts,” noted Anderson.

The Z-Tech designs from Robert Allan are classified by bollard pull. The current range is from the Z-Tech 2800, with a bollard pull of 28 tons, to the Z-Tech 7500, with 75 tons of pull, which tugs were built for Bay Houston Towing and Suderman & Young to work the LNG trade in Texas.

The 4500-class tug was adapted from the Z-Tech 6000, a 60-ton bollard pull tug designed for the Port of Singapore, to fit the Navy’s requirements.

The process of replacing the older YTBs in the Navy’s fleet of yard tugs began in 1997. At that time consideration was given to a number of design types including YTB conversions to z-drives. Two YTBs, including Manhattan were converted and delivered to Naval Region Northwest. Another two were upgraded with improved winch and power packages. However, it was subsequently decided to build new tugs, and the Z-Tech design met the three primary functions required by the Navy: ship assist, barge and general towing, and indirect escorting.

Anderson credits the conversions of two YTBS as a great improvement to the Northwest fleet, but shoehorning z-drives into a Navy single-screw hull also caused some problems. “The converted YTBs jump around on you and cavitate at times when you’re not expecting it during a submarine or surface ship move,” he said. “But now that we have a true ASD it’s like you’re floating into position on a cloud compared to the converted tugs.”

The prime contractor for construction of the four new Z-Tech tugs is Pacific Tugboat Service of Long Beach, Calif. This same company, which provides Navy and commercial tug services in southern California, was also the contractor for the two previous YTB conversion projects in 2007.

In both cases, Pacific Tugboat Service has contracted to convert or build the new tugs, which are subsequently sold to the Navy.

The first of the Navy new-builds, Valiant, is powered by a pair of Caterpillar 3512C main engines rated at 1,810 hp each at 1,600 rpm. The z-drives are Schottel SRP-1012 units with 83-inch propellers.

The firefighting system is an electronically controlled power take-off (PTO) from the starboard engine. The PTO engages a Stang fire pump. The system allows for the elimination of some piping and another engine to run the pump. The Stang monitor delivers 2,000 gpm at 150 psi.

Electrical power is delivered by a pair of John Deere diesel generators, each rated at 130 kW.

Because the tugs will come into contact with the hull of surface ships and submarines, they are equipped with Shibata non-marking gray extruded rubber, above and below the waterline. The fendering is designed so as not to leave marks on the gray hulls of Navy ships.

The accommodation deckhouse is completely separated from the machinery spaces, a configuration that provides a significant degree of noise reduction in the crew areas. The separation also makes it possible for the crew to gain access to the galley and staterooms in as dry a state as is possible within the wet envelope that often covers the Pacific Northwest.

With the full, rounded and raised stern (compared to the bow) the tug is well suited to perform actual towing stern-first in true tractor mode, according to its designer. In that configuration, the tow could be conducted using the hawser winch as a towing winch, Anderson said.

The 4500-class tugs are designed as day boats with a crew of four and accommodations for six. The tugs will be stationed at Naval Station Bremerton and Bangor Naval Submarine Base. They will also work at the Puget Sound Naval Shipyard at Bremerton and at Everett Naval Station. The crews are civilian, hired by the U.S. Department of Defense and employed by the Navy. Edit Module