New Navy tugs have the finesse, power for a wide range of dutiesJul 3, 2012 01:08 PM
When measured against the scale of February weather in the Pacific Northwest, it was a mildly miserable day in Puget Sound. But the gray backdrop did not dampen the showpiece sparkle of the tug Puyallup YT-806 moored at the J.M. Martinac Shipbuilding dock in Tacoma, Wash.
Puyallup is the fifth of six Z-Tech 4500 class tugs designed specifically for the U.S. Navy by Robert Allan Ltd., of Vancouver, B.C., to gradually replace its aging fleet of conventional, single-screw, 2,000-hp YTBs (Yard Tugs Big).
The first three — Valiant YT-802, Reliant YT-803 and Defiant YT-804 — are deployed in Naval Region Northwest, which includes the Naval Shipyards and Naval Station Kitsap at Bremerton, the Naval Submarine Base in Bangor and Naval Station Everett, to assist submarines, aircraft carriers and a full range of construction and fuel barges.
The naming of the remaining three — Seminole YT-805 (delivered), Puyallup YT-806 (delivered) and Menominee YT-807 (under construction) — reverts to a longstanding naval tradition of adopting Native American tribal names for its tugs. These three tugs will be stationed in Yokosuka, Japan, assisting the Navy’s vessels there.
A seventh tug — to be powered by batteries — is under consideration. “It is still being looked at as part of the Navy’s goal of reducing fossil fuel usage by 50 percent by the year 2020,” said Jay Anderson, port captain at Naval Stations Kitsap and Everett.
J.M. Martinac’s workforce is 20 percent Native American, and a dedication plaque hangs in the galley of Puyallup with a brief history of the local tribe, which has been supplying the yard with workers for many decades.
“That came about in the normal course of hiring,” said Jonathan Platt, vice president of the shipbuilding company that, during its 88 years of operation, has seen the city of Tacoma grow up around it. “There is no special hiring program.”
Puyallup measures 90 feet by 38.25 feet by 16 feet.
The propulsion chain comprises two Caterpillar 3512C diesels rated at 1,810 hp each, Twin Disc gears with slip clutches, Schottel SRP 1012 z-drives and 83-inch propellers in nozzles.
“A significant design change was the installation of a slip clutch to the port side engine for more balanced handling characteristics in 806 and 807,” said Anderson.
In the earlier tugs, there was a slip clutch on the starboard engine only, used to disengage the drive when operating the fire pump running off the front of that engine.
The power train delivers a bollard pull of 42 tons ahead and 45 tons astern and a free running speed of 12 knots. These figures represent a significant increase in the expected bollard pull of 38 tons.
The generous engine room, bright and uncluttered, gleams. The floor is covered with shiny aluminum plates with a five-bar checkered pattern for grip, and the machinery is painted white. The Stang fire pump system, driven by a PTO on the front of the starboard main engine, allows for the elimination of some piping and an extra engine. The Stang system delivers 2,000 gpm at 150 psi to two Stang monitors on the forward wheelhouse deck. Electrical power is delivered by a pair of John Deere 6081 diesel generators with 135-kW Marathon generators.
On the foredeck of Puyallup, which on a Z-Tech tug is the preferred working end, there is a JonRie 200 series single drum hawser winch with 400 feet of 7-inch, 12-strand Plasma rope from Puget Sound Rope.
The pilothouse is set much farther back and farther in from the sides than on a traditional tug so that the tug has greater visibility and can get in close under the flare of modern ships and carriers and work in the push or pull mode.
The Z-Tech has a flat forward sheer, and with the house set back, the crew has a flatter surface area with less sheer angle, or slope, on which to work. “Unlike the normal bow of a conventional tug,” Anderson explained.
The bow is also heavily fendered above and below the waterline with material from Schuyler and Shibata. This non-marking gray, extruded-rubber fendering is designed to be kind to Navy gray paint.
Z-tech tugs are designed with high sterns that are more rounded than the sterns of most tugs. “It is a Z-Tech tug feature, a seagoing stern,” said Anderson. “The pilothouse is aft and away from the working end, better able to work a ship’s bow, especially ones that have a radical flair, or wherever needed in close to push.”
With its higher stern profile, Z-Techs tow and transit in the true tractor mode, stern first. They are designed to exploit the best operational characteristics of tractor-style and ASD tugs, achieving close to omni-directional performance, as it applies to bollard pull and speed, traveling astern or forward. Therefore, only one winch, the hawser winch on the bow, is necessary for both shiphandling and towing operations.
Mounted aft of the house is what the Navy calls an accommodation ladder, or as it is called on the tugs, a brow. In essence, it is a gangway used to transfer personnel, or pilots, onto vessels alongside, such as submarines. Martinac constructed the brow to swing 180° and telescope out and across the rail and onto the vessel alongside.
Given the size of aircraft carriers in an era of muscle tugs boasting 60 or 70 tons of bollard pull, the Navy’s choice of a lower powered tug at first seems odd. But heretofore it has maneuvered its behemoths with single-screw, 2,000-hp YTBs. And, more importantly, the Navy has a wide range of smaller vessels and barges that require a more delicate touch than a powerful bitt- or chock-breaking wrench.
“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.”
The bonus in bollard pull is attributed to the Z-Tech hull design, several of which built at Martinac have shown the same increase in pulling power. Robert Allan classifies its Z-Tech designs according to bollard pull. For example, a Z-Tech 2800 has a bollard pull of 28 tons, a Z-Tech 7500, 75 tons of pull and so on. The Navy’s 4500 class tugs were adapted to fit the Navy’s requirements from the Z-Tech 6000 class.
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 were converted and delivered to Naval Region Northwest. Another two were upgraded with improved winch and power packages. However, the Navy subsequently decided to build new tugs, and the Z-Tech design could perform the three primary functions required by the Navy: ship assist, barge and general towing, and indirect escorting.
“The converted YTBs jump around on you and cavitate at times when you’re not expecting it during a submarine or surface ship move,” said Anderson. “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 Z-Tech tugs is Pacific Tugboat Service of San Diego, which also provides Navy and commercial tug services in Southern California. Pacific Tugboat Service has contracted to build the new tugs, which are subsequently sold to the Navy.
Noise and vibration reduction, a great contributor to crew comfort, is achieved in the Navy’s Z-Tech fleet with a separation of the accommodations and machinery areas. This is accomplished by an enclosed passageway between the two and a rubber strip sandwiched between deck levels. The separation also makes it possible for the crew to gain access to the galley and staterooms in as dry a state as possible. A generous application of insulation and friendly floor materials also contributes to a quieter environment within the house.
The pilothouse is tight but functional with a split console that affords a clear, unobstructed view of the bow winch through the floor-to-ceiling windows that circle the house. The windows — angled in and up to the pilothouse ceiling — give the captain and mate a good view of the ship while the tug is in close.
Furuno supplied most of the navigational equipment: the radar, electronic chart display and AIS. Raytheon supplied the Standard 22 gyro compass and ComNav supplied the 5001 series autopilot. Icom supplied the VHF and SSB radios.
The new boats are day boats with a crew of four. However, the crew has a full galley and four staterooms, two of which are singles for the captain and engineer and two are doubles, one each for the deck hands and other visiting personnel.
“Performance-wise the tugs have done everything we have asked and more,” said Anderson. “They are working very well for what they were designed to do and have outstanding creature comforts.”
In February, Puyallup was waiting for transport to Japan. Four pad eyes, built into the deck and used for lifting the tug aboard a heavy lift vessel, were virgin, unscarred by shackles. Puyallup, moored bow to bow with Menominee YT-807, still under construction, looked a far cry from the Navy’s fleet of aging YTBs.