U.S. Coast Guard buoy tender class
The Keeper class of coastal buoy tenders consists of fourteen ships built for and operated by the United States Coast Guard. The ships were launched between 1995 and 1999 and all remain in active service. Their primary mission is to maintain thousands of aids to navigation, both buoys and land-based. Their secondary missions include marine environmental protection, search and rescue, law enforcement, and light ice-breaking. 
The Keeper-class ships play a specific role in the Coast Guard's buoy tender fleet. They are primarily deployed to coastal areas such as New York Harbor, Chesapeake Bay, and Puget Sound, while the seagoing tenders of the "Juniper" class handle more off-shore areas, and inland tenders are assigned to the nation's large river systems. 
Origins and procurement.
In 1991, the average age of the twelve Coast Guard coastal buoy tenders approached 40 years, and the oldest was 52 years old. Maintenance costs on these vessels was growing quickly, and reliability was decreasing. One ship underwent emergency dry-docking to replace hull plates that had nearly rusted through. The obsolescence of the coastal buoy tender fleet came as no surprise, since some had been built during World War II, but it took several years for the Coast Guard, its parent agency at the time, the Department of Transportation, Congress, and private shipyards to deliver a solution. 
The coastal buoy tender replacement project originated in the Operations Directorate of Coast Guard Headquarters. The sponsor requirements documents generated there formed the basis for the work done by the Acquisitions Directorate. At this point, existing Federal Government regulations, notably Office of Management and Budget Circular A-109 dealing with major systems acquisition, specified much of the contracting process. 
The project was reviewed by the Transportation Systems Acquisition and Review Council and approved on 25 March 1992. Congress enacted $23 million for the first stage of acquisition in the FY 1993 budget. On 1 July 1992 a request for proposals was issued to the shipbuilding industry. On 12 March 1993 the technical and cost evaluations of the proposals were completed. On 17 May 1993 final contract negotiations were completed. On 1 June 1993 the Commandant of the Coast Guard issued a document titled "WLM(R) Circular of Requirements", specifying major aspects of the ships' design. On 22 June 1993, a contract was awarded to Marinette Marine Corporation to build the ships. Aspects of the acquisition process were criticized by the General Accounting Office. 
The contract was a firm order for detailed design and the production of the lead vessel in the class, , at a fixed cost of $22 million plus various performance incentives, with options for thirteen more ships, spare parts, and training. If all options in the contract were exercised by the Coast Guard, the total value of the deal was $291 million. The Coast Guard exercised options for three additional ships on 7 February 1996, six more ships in February 1997, and the final four in September 1997. 
At the time of the contract award, the Coast Guard announced its intentions to replace the eleven White-class and cutters still in service with the fourteen keeper-class ships. This saved maintenance expenses on the aging ships, and also significantly reduced personnel requirements through the introduction of advanced technology. While the Keeper class launched with a crew of 18, the Red and White-class buoy tenders they replaced had crews of 32 and 24, respectively. 
As the Coast Guard planned to replace its coastal buoy tender fleet, it also needed to replace its seagoing buoy tenders. This fleet also consisted of World War II ships that had served beyond their original design life. Thus, the history of the Keeper class is entwined with the seagoing "Juniper" class in a number of ways. Since the Coast Guard was replacing almost all of its saltwater buoy tender fleet, it considered the mix between seagoing and coastal tenders. This resulted in a buoy tender fleet with more of the smaller, cheaper Keeper-class ships, and fewer of the more expensive seagoing ships. Since both classes were designed in the same time period, they adopted similar technical solutions, such as Z-drive propulsion. All ships of both classes were built by Marinette Marine, and the construction overlapped. The Coast Guard placed a 60-person Project Resident Office on site at Marinette's shipyard to monitor and facilitate these two concurrent construction programs.
Construction and characteristics.
All fourteen ships of the Keeper class were built at Marinette Marine's shipyard in Marinette, Wisconsin. Their hulls were built of welded steel plates. The ships are long, with a beam of , and a full-load draft of . They displace 850 long tons fully loaded. Their gross tonnage is 904, and their net tonnage is 271. The top of the mast is above the waterline.
Rather than building the ships from the keel up as a single unit, Marinette Marine used a modular fabrication approach. Eight large modules, or "hull blocks" were built separately and then welded together.
The ships have two Caterpillar 3508 DITA (direct-injection, turbocharged, aftercooled) 8-cylinder diesel engines which produce each. These drive two Ulstein Z-drives. Keeper-class ships were the first Coast Guard cutters equipped with Z-drives, which markedly improved their maneuverability. The Z-drives have four-bladed propellers which are in diameter and are equipped with Kort nozzles. They can be operated in "tiller mode" where the Z-drives turn in the same direction to steer the ship, or in "Z-conn mode" where the two Z-drives can turn in different directions to achieve specific maneuvering objectives. An implication of the Z-drives is that there is no reverse gear or rudder aboard Keeper-class ships. In order to back a ship, the Z-drives are turned 180 degrees which drives a ship stern-first even though the propellers are spinning in the same direction as they do when the ship is moving forward. Their maximum speed is . Their tanks can hold of diesel fuel which gives them an unrefueled range of at .
The ships have a bow thruster. The Z-drives and bow thruster can be linked in a Dynamic Positioning System. This gives Keeper-class vessels the ability to hold position in the water even in heavy currents, winds, and swells. This advanced capability is useful in bringing buoys aboard that can weigh more than . 
Electrical power aboard is provided by three Caterpillar 3406 DITA generators which produce 285 kW each. Each ship also has a 210 kW emergency generator, which is a Caterpillar 3406 DIT.
The buoy deck has of working area. A crane with a boom long lifts buoys and their mooring anchors onto the deck. The crane can lift up to .
The ships' fresh water tanks can hold . They also have three ballast tanks that can be filled to maintain their trim, and tanks for oily waste water, sewage, gray water, new lubrication oil, and waste oil.
Accommodations were designed for mixed gender crews from the start. Crew size and composition has varied over the years. When "Ida Lewis", the lead ship of the class was commissioned in 1997, she had a crew of 18, commanded by a Chief Warrant Officer. By 2000 the crew had been increased to 20 personnel. Currently, the crew is 2 officers and 22 enlisted personnel.
Keeper-class hulls have a strengthened "ice belt" along the waterline so that they can work on aids to navigation in ice-infested waters. Not only is the hull plating in the ice belt thicker than the rest of the hull, but framing members are closer together in areas that experience greater loads when working in ice. Higher grades of steel were used for hull plating in the ice belt to prevent cracking in cold temperatures. Keeper-class bows are sloped so that rather than smashing into ice, they ride up over it and break it with the weight of the ship. The ships are capable of breaking flat, thick ice at .
Each ship carries a cutter boat on davits. They were originally equipped with CB-M boats which were replaced in the mid-2010s with CB-ATON-M boats. These were built by Metal Shark Aluminum Boats and were estimated to cost $210,000 each. The boats are long and are equipped with a Mercury Marine inboard/outboard diesel engine.
All 14 Keeper-class cutters are named after distinguished American lighthouse keepers.
In-service vessel sustainment.
Keeper-class ships were designed to serve for thirty years. In order to reach that goal, the Coast Guard has awarded class-wide contracts for a number of major maintenance items:
Ships in the Keeper class.
All of the ships were launched into the Menominee River in Marinette, Wisconsin. There they were completed and underwent builder's trials. When the Coast Guard accepted the ships, and ownership passed from Marinette Marine, they were placed "in commission, special" status. The crews were trained by Marinette personnel in Lake Michigan. They then sailed through the Great Lakes and out into the Atlantic to reach their new home ports. They made frequent stops. For example, "Henry Blake", which had one of the longer trips from Marinette, made port calls in four countries and eleven states. When the ships reached their new homes, a public commissioning ceremony was held, and the ships were placed "in commission, full" status. 
References.
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