WPB 110' Island Class
The United States Coast Guard acquired forty-nine 110' ISLAND Class patrol boats, of which forty-one remained in service as of early 2012, the others having been withdrawn from service following an unsucessful conversion to the WPB 123' configureation. The ISLAND Class' missions are to provide offshore surveillance, law enforcement, and perform search-and-rescue (SAR) operations. As such, the patrol boats were designed to have a 5-day endurance and a 3-ton payload margin. These boats replaced the Coast Guard's 95' and 82' patrol boats in this role. Originally, a construction contract for sixteen 110' boats was awarded in Fiscal Year 1984 (FY84) to the Marine Power and Equipment Company of Seattle, Washington. However, a United States District Court disallowed the award because of irregularities in the procurement process. As a result, Bollinger Shipyards in Lockport, Louisiana was awarded the contract for the 16 boats in August 1984.
In FY86, the U.S. Navy purchased an additional sixteen 110' patrol boats for the Coast Guard under the Department of Defense (DOD) Augmentation Appropriation. Next, the Coast Guard purchased five more patrol boats under the Anti-drug Abuse Act of 1986. All of the above mentioned procurements plus the final 12 boats were awarded to Bollinger Shipyards. The cost per patrol boat was approximately $7 million. The boats of the 110' ISLAND Class were commissioned between November 1985 and 1992.
At the time of contract award the design of the ISLAND class was approximately 20 years old. The design is based on an existing patrol boat developed by the British firm, Vosper Thornycroft (UK) Ltd. Such a route was chosen in order to minimize procurement costs and ensure the Coast Guard obtained a proven design. The ISLAND Class has a steel hull with aluminum deck and superstructure. In addition, they have a flush-deck with a round-bilge planing hull that is equipped with an active fin stabilization system.
However, after the first boats came into service it was discovered that the ISLAND class suffered from hull problems, most notably the development of cracks when operated in heavy seas. As a correctional measure, heavier bow plating was added to patrol boats WPB 1317 through WPB 1349. Other changes include an improved water purification system, and improved habitability and mooring fittings. Because of this and other modifications the patrol boats are grouped in A (WPB 1301-WPB 1316); B (WPB 1317-WPB 1337); and C (WPB 1338-WPB 1349) series.
The Island class has a round-bilge planning hull equipped with a active fin stabilization system. The hull was constructed in an inverted position to achieve better hull fairness. The steel hull and aluminium superstructure is bonded together using the Detacouple technique. The class is designed with a five day endurance.
There are three variants of the Island Class. The A & B classes use two Paxman-Valenta 16 CM engines as there propulsion plants while the C class uses two Caterpillar 3516s. Electricity is supplied by two 99 KW Caterpillar 3304T diesel generators capable of parallel operation. ATTU (WPB 1317) the first of the "B" class and all subsequent 110's have heavier bow plating to correct a hull cracking problem experienced in earlier "A" class vessels. Differrent armaments also distinguish the differrent variants as the A & B cutters have one 22mm machine gun and two M60 light machine guns and the C cutters are armed with two 50 caliber machine guns in addition to the standard weapons.
The first eight 110s were based on the East Coast in the 7th District. The ninth and following WPBs were spread around the country to Florida, Virginia, Alaska, Massachusetts, California, New Jersey, Alabama, Georgia, South Carolina, Oregon, Hawaii, Maine, Texas, and Guam. Today, several of the WPBs around the Gulf Coast and elsewhere along the East Coast have been, or are being moved to the 7th District in order to support drug interdiction efforts. Typically, Southeast Coast WPBs operate in the Atlantic Ocean and Caribbean Sea, with drug interdiction, LE, and SAR as primary missions. WPBs in the Northeast operate in the Atlantic, primarily providing fisheries law and SAR support, and also perform at least one District 7 patrol per year. West Coast WPBs generally operate in the Pacific Ocean and the Gulf of Alaska, with enforcement of fisheries laws, LE, and SAR as primary missions. WPBs in southern California are increasingly being called upon to assist in drug interdiction efforts.
The Coast Guard retrofitted all 49 Island Class patrol boats with the stern flaps. Plans are also being made for the installation of a stern flap on a Hamilton Class cutter. A large, 18-foot hydrodynamic hull model was constructed for use with stern flap optimization resistance tests, spray rail evaluation, and the prediction of resistance and estimated thrust needed for a new propeller design. Stern flap designs were model tested for a systematic investigation regarding the effect of varying the chord length, span, angle, and planform area distribution. The final selected flap design minimized the estimated fuel usage over a range of operating conditions that included two displacements and a varying speed-time profile from 12 to 30 knots.
The selected stern flap is predicted to increase the full load maximum speed by 0.8 knots to 27.85 knots. At the 24-knot cruise speed, a 3.7 percent reduction in delivered power is predicted. The annual fuel savings for the prescribed displacements and operational speeds is estimated to be 13,000 gallons per patrol boat annually.
Observation of the flow patterns and model trim during the resistance testing indicated the need for a supplementary spray rail. Discussions with the USCG boat operators indicated that additional spray suppression was needed and is now included in the ship alterations package.
A new Island Class propeller design to accompany the stern flap installation was undertaken with the goal of increasing fuel economy, reducing airborne noise, and improving engine reliability by providing proper engine loading. Special attention was paid to the suppression of root cavitation. The relatively simple wake field permitted accurate quasi- calculations modeling the blade and the hub were used to iteratively alter blade shape to achieve satisfactory performance. Model-scale open water and cavitation tests will not be conducted. The confidence in this propeller design is based on the NSWC experience gained from design, model test, and full-scale trial data on the PC 1 Cyclone Class propeller, which has operational conditions similar to that of the Island Class propeller.
The new propeller design is predicted to be an average of about 8 percent more efficient than the existing fleet propeller throughout the speed range. In addition, it will be free of thrust breakdown due to cavitation. With the stern flap, spray rails and new propeller, the maximum speed is predicted to be increased by 2.5 knots to 29.6 knots in the full-load condition. The speed increase is due to reduced resistance, greater propeller efficiency, and increased available engine power due to a better fit between the propeller power curve and the envelope of available engine power.
Combatant Craft Department (CCD), Code 23 completed the design, manufacture and kit production of a prototype combustion air silencer for the USCG 110' WPB Island Class Patrol Boats that are equipped with Paxman diesel engines. CCD performed a shipcheck of the CGC Aquidneck with the intent of designing the subject combustion air silencing system. In conjunction with the shipcheck data and a previously developed combustion air silencing system for the 170' PC, CCD produced production, ripout and installation drawings for the construction and installation of the combustion air silencer system. The kit has been delivered to the USCG Integrated Support Command Portsmouth, Virginia for installation.
These WPBs are constructed of a lightweight mild steel hull joined to an aluminum superstructure. In order to optimize performance, the hull plate thickness varies from 4# to 10# plate depending on hull location. Early on in its service life, the A-Class WPBs underwent a structural SHIPALT that installed intermediate frames between those originally installed and corrected some structural details. The B and C class WPBs were constructed with a structural layout similar to that of the modified A Class. As a result, although the B and C classes have other tankage and arrangements differences from the A class, they are comparable from a structural standpoint.
An overriding issue is that some areas in the cutters are very difficult, and in some cases impossible, to preserve. Tight machinery installations, small spaces, closely spaced stiffeners, and totally inaccessible tank areas together with a bilge and interior drainage system is most charitably described as uninspired combine to make corrosion a maintenance nightmare and in some cases a serious structural problem. This problem is present to a greater or lesser extent throughout the fleet, but are far more noticeable in the WPBs stationed in the South Florida and Puerto Rico. There, hot, humid, rainy weather and increased operating tempo conspire to age the WPBs far more rapidly than elsewhere.
The hulls and supporting structure in the Caribbean WPBs that are more than one year out of dry-dock are in generally only fair condition due to advancing corrosion. Flaking rust on the stiffeners is common, even on cutters relatively fresh from dry-dock. Pitted and corroded plating is routinely painted over without surface preparation due to the very real fear that the power cleaning will penetrate the hull.
Particularly severe problems were found in specific locations on the cutter. These areas include: the forepeak; void under the forward crew head; inaccessible areas in the forward auxiliary space; under the roll fins and water maker in the machinery space; skeg tops throughout the cutter; under the towing hawser reel in the battery compartment; the area around Bulkhead 28, including the gray water / oily water / bulkhead intersection, as well as the bulkhead itself where the corrugated plate meets the vertical plate; and under acoustic insulation tiles in the lazarette and battery space. In these areas, it is common to find corroded shell plating painted over, many successive stiffeners flaking or otted to one half the original profile, and evidence of prior metal replacement.
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