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Patrol Boat

The patrol boat is a small combat ship that uses heavy machine guns as its main weapon for offshore operations. It can undertake patrol, alert, mine and other tasks. Many countries do not even have equipped troops, but paramilitary coast patrols or police officers, used to check the daily routines. There are many designs for this type of ship. They can be used in the navy, the coast guard or the police. It can operate on marine environment or on rivers. This type of vessel is often found involved in missions to protect the territorial waters and borders, to defend against infringement of sovereignty, to combat smuggling, to fight illegal fishing and to participate in rescue operations. They are also known to be involved in rescue and anti-piracy missions.

The patrol boat has a small tonnage, high speed and flexibility, and the displacement is usually tens of tons to hundreds of tons. The speed is 30 to 40 knots, some can reach 50 knots, and the cruising capacity is 500-3000 nautical miles. Some speedboats are also equipped with 20 to 76 mm caliber guns. Larger tonnage boats may also contain mines and depth charges. The matching sensor system includes search, detection, weapon control, communication and navigation, and electronic warfare.

As an independent class, anti-submarine defense ships were introduced into the Great War due to the fact that submarines , which were originally supposed to be used for limited purposes near bases, from the first days of the war showed their high tactical qualities and combat effectiveness. For the first time, an urgent need arose for smaller, less expensive ships, compared to destroyers , capable of withstanding an underwater enemy. It took a special ship capable of searching for submarines, escorting transport vessels, and carrying out patrol service near naval bases. The destroyers could successfully solve these problems, but they were clearly not enough in quantity. Possessing considerable firepower, the destroyers were attracted mainly for other combat missions, the sector of which was greatly expanded.

England was the first to start an intensive search for forces and means to combat German submarines, develop tactics for anti-submarine warfare, and improve anti-submarine weapons and weapons. Thus, for the first time in the world, the first anti-submarine ships appeared in the British Navy during the First World War in connection with the active operations of German submarines. Then in England they began to build patrol ships - the Pi-Bots with a steel nose tusk (displacement of 573 tons, full speed - 22 knots , one 100-mm gun, two 2-pound guns, two torpedo tubes, depth charges). For the American fleet, following the example of the British, they urgently laid down about 60 units of ships similar to the TFR - such as the Eagle. In the Russian fleet, ships similar to the English anti-submarine defense ships were designated by the classification term "Watch ship".

Marine patrol boats are usually about 30 m (100 ft) long and armed with a medium-sized naval cannon as the main weapon and other auxiliary weapons such as machine guns or close-combat systems. Depending on the purpose of use, ships can be equipped with more sophisticated equipment such as sensor systems, torpedo tubes, anti-ship missiles or air defense. They are often used for patrolling in national exclusive economic zones. With the main task is to combat violations of sovereignty, combat illegal fishing, fight smuggling, fight illegal immigration, fight pirates, search and rescue. Large patrol vessels may have additional landing zones and helicopters, in the event of a war patrol vessels can assist large battleships in combat.

Most modern designs use gas turbine engines and have a speed of 2530 knots. Patrol boats and other relatively heavy boats are generally propeller driven. The conventional drive system includes high speed, fast engines which have a high power/weight ratio. There are known racing boats with water jet propulsion systems, but such systems are relatively new and more expensive than traditional propeller propulsion systems, as well as being less efficient in fuel consumption at certain speeds.

The small size means they are the lowest cost of warships built in the navy. All naval forces in the world have at least one patrol ship operating offshore or on the river. With their high speed and maneuverability, they are very useful on small or offshore waters. A fast patrol boat might typically be used for Customs and Excise, Coast Guard, Fishery Protection, Military and Police duties.

In boats which are capable of operating in a planing mode, especially near the stern where the weight of the boat is supported in the planing mode, the hull is usually "V" shaped in cross-section, each arm of the "V" being virtually flat and subtending an angle of less than 25 or 30 degrees to the horizontal, in order that planing can be sustained. For a planing boat, the volume of water displaced at rest is usually at least five or ten times the volume of water displaced when the boat is planing.

Such a planing boat suffers from several disadvantages. Firstly, it is uncomfortable to ride in, especially in high sea states. This is because when the bows hit a wave it has a tendency to "slam" into that wave, causing discomfort and possible injury to passengers. Secondly, this slamming behaviour can significantly reduce the life of the structure of the boat owing to the high structural stresses that it can cause. Thirdly, the boat may not behave uniformly well at all speeds. At very low speeds it may behave as a typical "displacement" boat, as discussed below. As such, it may ride fully in the water without displaying any planing behaviour.

At high speeds, it may behave fully in a planing mode. However, at intermediate speeds, as it attempts to surmount its own bow wave in order to achieve the planing mode, its behaviour may be less predictable, since it may intermittently achieve and then fail to achieve the planing mode. Finally, for a given weight of boat, the power required to surmount the bow wave and achieve the planing mode is very significant. This power requirement can be a serious limiting factor on the amount of fuel carried and hence on the range of the boat.

An alternative to a planing boat is one which behaves in a displacement mode, in other words, a boat which behaves according to the displacement rule. Such boats do not display any significant planing behaviour, but rather have a maximum speed which is limited by the drag losses of the boat hull as it moves through the water. The displacement rule postulates that the maximum achievable speed (in knots) is proportional to the square root of the length of the boat (in feet). The constant of proportionality has been found empirically to lie usually between 1.3 and 1.6. Hence displacement boats have a speed which is limited by their length. The speed of such a boat is insufficient for the present requirement of a light manoeuvrable fast patrol boat or the like.

An alternative to a boat which behaves either in a displacement mode or a planing mode is one which behaves in a so-called "semi-displacement" mode. Such a boat is relatively slender (say, having a length to beam ratio (a "slenderness ratio") of greater than 5 to 1, 6 to 1 or even 7.5 to 1). On the one hand, it does not have a maximum speed limited by the displacement rule, whilst on the other hand it does not exhibit any significant planing behaviour since it does not generate a bow wave of any magnitude over which it can rise. Hence boats which behave in a semi-displacement mode do not in general suffer from the disadvantages of boats which behave either in a displacement or a planing mode of, on the one hand, lack of speed, or, on the other hand, lack of range.

The major disadvantage with a long slender semi-displacement boat is its tendency to be unstable, especially in roll. Such roll instability is commonly caused by two factors. Firstly, the very slenderness of the boat means that there is little resistance to roll. Secondly, such a boat tends to have a hull surface which is deliberately designed to avoid planing, and hence has few sharp edges such as might increase roll damping due to vortex shedding off those sharp edges.

One solution to such a problem has been adopted in catamaran or trimaran configurations. Here stability in roll is achieved by connecting two or more slender semi-displacement hulls so as to be spaced apart from each other. Catamarans or trimarans suffer from two main disadvantages of relevance. Firstly, they can be awkward to manoeuvre and handle. Secondly, they can have no passive self-righting capability since they are equally stable inverted as they are the correct way up.

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Page last modified: 14-10-2019 19:10:23 ZULU