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WTGB-140 Bay-class - Large Icebreaking Tug

The 140-foot Bay class Cutters are state of that art icebreakers used primarily for domestic ice breaking duties. They are named after American Bays and are stationed mainly in the northeast United States and the Great Lakes. The Coast Guard had the 140-ft WTGB class of ice breaking tugboats designed and built to replace the 110-ft WYTM class. The new tugboats have a greater horsepower than the 110-ft WYT and are larger.

WTGBs use a low pressure air hull lubrication or bubbler system that forces air and water between the hull and ice. This system improves icebreaking capabilities by reducing resistance against the hull, reducing horsepower requirements. The bubbler system is divided into 4 sections, port forward, starboard forward, port aft, and starboard aft. The two forward portions vent through the piece welded to the bottom of the forward keep, while the two aft sections have holes in the hull to form a channel. The air pumped through these holes helps lubricate the hull for icebreaking, reducing frictional resistance of the ice.

A single four-bladed propeller 8 ft-6 in. in diameter, operating in a conventional aperture with the rudder immediately aft, drives the KATMAI BAY. The propulsion motor is directly coupled to the propeller shaft. The propulsion motor is a d.c. motor rated 2500 SHP at 245 and at 305 rpm, corresponding to the bollard speed and free route speed of the tug, respectively.

The R&D Center conducted tests on the 140-foot WTGB, KATMAI BAY, during the winter of 1978-79. These tests indicated that the WTGB met or exceeded its design requirements. CGDNINE gained further experience with the class during the winter of 1979-80. As a result of this testing and experience, it appeared likely that two WTGB's, working together, might be as capable as a single WAGB. If two WTGB's are as capable as a WAGB, then it is much more economical to conduct operations using two of these tugs instead of a larger WAGB.

One of the drawbacks of the 140-foot WTGB's is the limited crew size which restricts operations to approximately 24 hours between rest periods. The WAGB's have essentially unlimited endurance from a personnel standpoint. The endurance of the 140-foot WTGB will be a significant limitation unless crews are rotated or some other crewing concept is adopted.

The Coast Guards In-Service Vessel Sustainment (ISVS) project will help vessels meet or exceed their designed service life through a recapitalization of targeted hull, mechanical, electrical (HM&E), and electronic systems. The ISVS program reflects a positive future for the Yard as the shipyard provides expertise and best value to the Coast Guard for maintenance of cutters that are in need of a mid life renovation to meet their intended service life. To sustain mission effectiveness, the Coast Guards near-term ISVS projects for the Yard include SLEP repairs and dry-docking of the 140 Icebreaking Tugs (WTGB).

Once the cutter boat arrives at the Yard for the production work to begin, the new systems are installed, as built drawings developed and the usual prototype design changes are implemented. There is also the advantage of combining this renovation work with routine maintenance items such as drydocking, painting, plate renewal, etc. and the usual surprises found on old cutters once systems are removed like rusted steel, worn machinery parts and things of that nature.

Major SLEP work items include renewal of the crews berthing and messdeck, comprehensive navigation and steering systems upgrades, main propulsion motor overhaul, and installation of a new engine room water-mist fire fighting system and a modern small boat davit system. Additionally, the icebreaking bubbler system located on the fantail was decommissioned, and a new bubbler system was installed in the engine room. This large diesel engine and its compressor required plenty of space, so the ships service diesel generators were moved to make room. The cutter was also sandblasted and painted top to bottom, stem to stern.

The Tridentis Team provided a range of engineering services and program management support for the Service Life Extension Program for the 140 WTGB Icebreaking Tugboats. Tridentis performed systems design and engineering analysis in support of the USCG Surface Forces Logistics Center (SFLC), including marine/mechanical engineering, electronic engineering, naval architecture, and engineering specialty disciplines.

Tridentis designed a replacement for the existing steering machinery. The team investigated the various system configurations for faults using the casualty repair data to perform a root-cause analysis, proposed replacement of outdated equipment that was unsupportable, interacted with multiple vendors performing a market analysis of current replacement equipment and designs, and completed a design study outlining the recommendations including a cost estimate, weight and moment impacts, a 3D digital model showing equipment size and clearances, and developed a procurement specification.

Tridentis tracked the weight and moment stability impacts for the total SLEP equipment removals and replacements. This was a critical function due to the fact that most ships late in their life cycle will have used up much of the initial margins built into the design. The centers of gravity and displacement were plotted on the allowable KG curve to show the improved stability resulting from the changes.

The Morro Bay, the first U.S. Coast Guard 140 ft WTGB icebreaking tug to undergo a 14-month Service Life Extension Project (SLEP) at the Coast Guard Yard in Baltimore, MD, returned to homeport of Cleveland, OH in September 2015. After nearly three decades service they were now ready for the SLEP, a major mid-life overhaul expected to extend their service life by 15 years. The first WTGB SLEP was scheduled for 12 months; however, once the Yard achieved a satisfactory production labor learning curve (anticipated after Hull #3), the Yard will complete two 140-foot WTGB SLEPs per year, with an anticipated duration of 9 months each.

The U.S. Coast Guards seventh 140-Foot icebreaking tug, USCGC Thunder Bay (WTGB-108) arrived at the Coast Guard Yard in Curtis Bay, Maryland, Nov. 7, 2017, to begin service life extension work as part of the In-Service Vessel Sustainment (ISVS) program. The U.S. Coast Guard (USCG) cutter, USCGC Sturgeon Bay (WTGB-109) departed the Coast Guard Yard in Curtis Bay, Maryland, Nov. 17, 2017, following completion of service life extension work as part of the In-Service Vessel Sustainment (ISVS) Program. The ship was the fifth of nine 140-foot icebreaking tugs to undergo a service life extension project through the ISVS Program.

The SLEP program seems to be operating on a "last in / first out [LIFO]" schedule, in which the newer vessels are being SLEPed before the older units are updated.



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Page last modified: 18-04-2019 14:30:23 ZULU