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Further Reading

Worldwide Frigates and Corvettes

Modern surface combatants - which include cruisers, destroyers, frigates and corvettes - are the workhorses of the fleet. Corvettes and frigates play a dominant role in most navies. The term "Frigate" may be applied to ships with over 3,000 tons of displacement to as much as 7,500 tons. (By comparison, an Oliver Hazard Perry frigate displaces about 4,000 tons.) Corvettes are small, maneuverable, lightly armed warships (between the size of a patrol boat and a frigate) that various countries use for coastal duty.

Corvettes typically provide nearly all the striking and sensor power of a frigate in a smaller platform. The corvette is generally defined as a heavily-armed small surface combatant measuring 55 to 100 meters in length and displacing up to 500 to 2,000 tons. A distinguishing feature of the corvette is her capability for limited independent deployment, typically between 10 to 20 days, and usually equipped with self-defence capability against air and submarine threats. It is often also helicopter-capable - sometimes even affording her own hangar. Such craft can take on at least an ASM-armed helicopter at standoff ranges up to 13km.

It is difficult to establish a distinction between frigates and corvettes, inasmuch as even the displacement cannot be used as a basis of classification. Ships which would be designated in one navy corvettes, are called frigates in another. A ship the size of a small frigate or large corvette, on the order of 3,000 tons, provides a good balance between payload and endurance. It can deploy reliably overseas while having enough room for acceptable crew facilities, and it is the smallest ship deemed capable of supporting a single medium-sized helicopter.

AMI forecast that between 2010 and 2030 the US market will make up 63% of the world's future spending on aircraft carriers and large expeditionary ships, 39% of the world's investment in cruisers and destroyers, 37% of world submarine spending, and 23% of the global market for frigates and corvettes. The US naval and maritime security market is expected to remain the largest in the world over the 20 years 2010-2030. A Coast Guard study in 2002 estimated that the projected global market for frigates, corvettes and off-shore patrol vessels over the 15 years 2002-2017 was $57 billion. The Another 2010 estimate of the market for corvettes over the ten years 2010-2020 pegged the value at up to $4.5 billion based on an average vessel unit price of around $215 million. The size of this potential market indicates that the corvette is still a vessel in high demand and the sheer versatility of these vessels is the secret of their appeal.

Most countries have navies that greatly resemble the U.S. Coast Guard. They operate primarily along their country's coasts. Their missions focus mostly on search and rescue, smuggling and fisheries enforcement, and they sail relatively inexpensive, small ships. The great strength of the corvette and frigate is that they both offer a design, albeit of a different sizes, which can operate either independently, or as part of a taskforce. Whether on national missions or UN deployment, their main tasks are the protection of territorial waters, participation in global peace-keeping measures and cooperation in crisis management. They must be able to successfully counter threats from other surface vessels, submarines and aircraft. With these vessels, reliability, availability and minimum crew size are top priority factors. Long-range capabilities for patrol missions, long sea endurance in conflict areas and high speed for rapid redeployment to far-off theaters of operation are just as indispensable.

A frigate in the days of wooden war vessels was the designation of a full-rigged ship with two decks, and so distinguished from a ship of the line which had three. In large fleets, three-deck ships of the line had the advantage of overlooking those of inferior rates with the fire of their main and upper decks. Their imposing mass often contributes to ensure victory, solely by the impression of terror which they produce on board the enemy's ships which are not so high.

In time frigates were designed to ensure speed and ease in working them, while they remained of moderate size. After 1600, the frigate type became more or less fixed although a rigid adherence to a single form was not demanded until about 1750, after which frigates were classified as forty-fours, thirty-eights, thirty-sixes, thirty-twos, twenty-eights and twenty-fours; this classification being made on the basis of the number of guns aboard. In the British navy the tonnage of frigates was from 500 to 1,200, while in the early days of the United States navy, vessels over 1,200 tons were at times classed as frigates. Frigates were usually fast sailers, mounted with 28 to 60 guns, and were employed as scouts and as cruisers, to convoy merchantmen, etc. This sort of vessel seemed the most proper for independent cruising on distant expeditions.

The great battle of the Nile in 1798 was the most brilliant, and the most important of the scenes ot naval engagements which sustained the reputation and assured the safety of the British Empire from the arrogance of the common enemy of Europe. The victory would have been complete, had any frigates and small craft been attached to the British squadron. With such auxiliaries, none of the French transports in the harbour of Alexandria could have escaped destruction. "Were I to die at this moment," writes Nelson in one of his despatches, "want of frigates would be found stamped on my heart." Nelson was in want of frigates, - the eyes of the fleet, as he always called them : - to the want of which, the enemy before were indebted for their escape, and Bonaparte for his arrival in Egypt.

In the early 19th Century the British Empire possessed an immense number of ships of the line, and frigates. The Lords of the Admiralty would have thought that they were lavish of the finances of the three kingdoms, if they had caused new vessels to be constructed for such an unequal contest; it appeared to them sufficient to set apart for it, some of those with which their ports were crowded. The Americans, on the contrary, whose naval force at that time was inconsiderable, perfectly understood, that if they confined themselves to building vessels similar to those of the English, they would remain constantly inferior to them; and with a calculation, the justice of which was proved by the event, they sent to sea frigates respectively stronger than those of their adversaries. It followed that every time an American frigate met an English frigate alone, the latter was overpowered.

The terms frigate and corvette, which before the introduction of heavy guns designated well-defined types, were nevertheless used quite arbitrarily. In the age of sail, the original classification into ships of the line, frigates, and corvettes called all cruisers with covered batteries frigates, and limited the term corvette to those ships which were flush-decked with no covered batteries. In the late 19th Century, ships with 'tween deck batteries were called frigates or 'decked' corvettes. Ships with open batteries were called 'flush' decked corvettes.

Before the days of the steam turbine and steel hull, a corvette was larger than a sloop, but smaller than a frigate and usually characterised by a single gun deck. Their tasks would include small-scale combat, 'showing the flag' of a country around the world, or supporting larger fleets of bigger ships. Capable naval platform that helped to protect the convoys, in some ways corvettes are odd vessels; bigger than an offshore patrol craft, but lacking the size of a frigate; a bridge between a navy's brown-and blue-water capabilities.

With the miniaturisation of today's electronic systems, vessels of corvette-size are able to pack in more technology than previously thought possible. The development of space-saving multi-purpose devices from video-displays to missile launchers allow more by the way of weaponry, electronics and computing equipment. Already able to fit in a variety of SSMs like the Exocet and Harpoon, these fittings extend to SAMs and torpedoes.

New lightweight and compact air detection and defence systems were rapidly developed. The Sea Sparrow ship-launched, point-defence missile has semi-automatic/automatic modes with vertical-launch options. Vertical launch systems reduce the space taken up. Fully containerised Israeli IAI Barak vertical-launch AA missile launchers are available with particular attractiveness, as they require no deck penetration for fitting. Matra has also developed the Mistral launcher, designed for use on small vessels against aircraft and helicopters within the 4 to 6km range. The ubiquitous 76mm OTO Melara also has an upgraded super rapid-fire version to cope with air threats. Close-in weapon systems (CIWS), once thought of as suitable for major surface combatants now also have versions, like the Breda Twin 30mm guns, suitable for corvettes.

The larger build of the corvette comes along with the advantages of longer range and better seakeeping. This extra range is a consideration in view of the tighter defence budgets with the recent economic downturn. The new corvette would be expected to fulfil a multi-role function that goes beyond her current limit for strike operations.

Today, the maximum practical speed of displacement ships is about 32 to 35 knots. This can be achieved in a relatively small ship by making it long, narrow and light but also costly. There are major problems in delivering this power efficiently through conventional propellers due to cavitation problems and using conventional diesel or steam machinery which provide a very poor power/weight ratio. Modern large ships have traditionally been propeller driven with diesel power. Propellers are, however, inherently limited in size, and they also present cavitation and vibration problems. It is generally recognized that applying state-of-the-art technology, 60,000 horsepower is about the upper limit, per shaft, for conventional fixed pitch propellers. Moreover, diesel engines sized to produce the necessary power for higher speeds would be impractical because of weight, size, cost and fuel consumption considerations.

Another means to achieve high speed ships is the planing hull. This popular design is limited to a very short hull form, i.e. typically no more than 100 feet and 100 tons. If a 50 foot boat is scaled to the length of a frigate of 300 feet, the speed scales to the precise range of 12 to 60 knots. Thus scaled, the power required for a 300 foot planing frigate would be about half a million horsepower. Furthermore, the ensuing ride on this 300 foot ship would cause material fatigue as its large flat hull surface would be slammed at continuously high speed into the ocean waves inasmuch as it would be too slow to plane or "fly" across the waves as a much smaller planing ship would do.

Structural additions of various kinds and configurations have been implemented for various types of marine vessels in order to improve powering performance. Some very small pleasure craft and planing boats have been provided with adjustable trim flaps (trim tabs) for controlling the trim. As for combatant vessels, during World War II some small German ships were provided with stern wedges for the purpose of improving powering performance. Until the early 1980's, however, neither stern wedges nor stern flaps were known to be pursued by anyone for combatant ships of the frigate/destroyer size (approximately 3,000 to 10,000 Long Tons displacement). In the 1980's some navies began to successfully apply stern wedges to larger ships up to the frigate size.

A stern wedge design was initially attempted by the U.S. Navy for the FFG 7 frigate class; however, in the course of model testing it was discovered that a stern flap was more effective than a stern wedge on this class. The model tests demonstrated approximately a 5% decrease in delivered power at speeds of 20 knots and above. In 1989, a stern flap was designed and retrofitted by the U.S. Navy on the USS Copeland frigate (FFG 25). Analysis of the ship trials data for the USS Copeland frigate having a retrofitted stern flap indicated an 8% power saving, somewhat greater than the model test results, and increased top end speed.

Helicopters have now become entrenched as an integral part of the weapons system carried by destroyers and frigates in anti-submarine search and strike capacity. Invariably, landings and take-offs of these helicopters from vessels must be made in moderate to severe turbulence and once on the deck, the helicopter must be quickly secured and stored for protection from the environment.

Use of remotely piloted vehicles (RPV) or unmanned air vehicle (UAV) in the Naval environment [Shipboard Launch and Recovery system (SLAR) [also known as Launch, Recovery Securing, Handling (LRSH) Equipment of the RPV] adds a number of new challenges. For the proposed short range RPV in particular, operating from frigate sized and smaller ships means taking off from, and landing on, an unstable moving deck, with severe airwake turbulence from the superstructure and very tight space constraints both during operation and stowage. A strong trend is already emerging in favour of RPVs with a VTOL capability for the maritime role because of the demonstrated difficulties of landing a fixed wing air vehicle on even relatively large and stable ships' decks.