Author: David M. K. Brown, George Moore
Translations: Wang Xin, Cocoon, Yu Yaodong
The Royal Navy learned a lot from post-war target ship testing. In particular, the destructiveness of underwater explosions to the stern. Like the Scorpion in this photo.
"Stay afloat, stay mobile, keep fighting."
Admiral Lord Charterfield once said: "Warships are used for combat, and they need to be able to attack both on their own initiative and in the ability to withstand attacks." "At the beginning of World War II, almost as many destroyers were damaged each year as there were in service, and sixty percent of the frigates in the Falklands War were damaged. Even in peacetime, warships are more vulnerable to accidental damage than merchant ships.
To keep the ship from damage, the first line of defense is active defense (either preemptively attacking the enemy's base, destroying the platform before the enemy fires its attack weapon, or destroying missiles in flight). Some argue that, given the lethality of modern weapons, ships should focus their defenses on active defense. But in any case, being hit is always unavoidable, so passive defense must also be taken seriously to minimize the impact of being hit. But it's not easy to strike a balance between active and passive defense, and it's also not easy to strike a balance between defensive performance and other performance.
Threats to ships can be divided into three categories: accidents, terrorist attacks and enemy attacks. Accidents include fires and explosions (98 major incidents), collisions (125) and strandings (50), and the figures in parentheses are the number of such accidents caused by the British Navy between 1945 and 1984. (7) Although terrorist attacks are relatively rare, their potential threats still exist, such as the US Navy's "Kohl" destroyer in Yemen in 2000. The variety of weapons that can be used against battleships is dizzying, but regardless of the weapon, its lethal effect can be considered in six ways: fire, water ingress, structural collapse, vibration, shock wave, and the impact of fragments.
(Above) The Sheffield is on fire.
Non-contact underwater explosions such as sunken mines and torpedoes can cause rapid and violent deformation of the hull, causing the hull girder to bend and collapse, which is the most common cause of destroyer loss during World War II. Although there are currently no effective measures to provide this protection for ships, there are some measures that can improve this: avoid discontinuities in the main structure, such as fractures at the bow, etc.; ensure that the overall design stress is kept at a low level by increasing the depth of the keel to the deck; and the shaft system seal through the bulkhead adopts a movable design, so that there can be a large relative movement between the shaft and the structure. The radius of death of these near-blow weapons is generally quite small, and the above measures will further compress the radius of killing. Contact-explosive torpedoes and mines still pose a threat to warships (as in the 1991 Gulf War): World War II-era torpedoes typically explode a 30-foot-long, 15-foot-tall burst and break twice as wide into the water.
The impact of the explosion can cause the equipment on board to move significantly and cause damage to it. The hull should avoid the use of cast iron, but also avoid the use of suspension (cantilever) to install heavy objects. Mounting the device on an elastic base can reduce the impact of shock. These measures are very effective, and these impact damages are relatively rare, and some people even suggest that the anti-impact protection measures be abolished. Each new type of warship requires high shock payload tests to ensure the effectiveness of its impact response measures.
Underwater weapons will certainly cause the ship to enter the water, which will cause the ship to sink (usually in the form of capsizing) or the engine room to flood, making the ship unable to sail. The British Navy's frigates were able to ensure that any 3 cabins were flooded, but surviving in the event of 4 cabins being submerged was a really lucky thing (the Falkland Islands War Coventry sank after all 5 cabins were flooded). The cabin could also be attacked by air-launched weapons, and the unitary arrangement could provide good survivability, as early as the First World War, the British Navy's cruisers introduced a unitary arrangement. The simplest unitized arrangement of steam turbine-driven ships is to alternately arrange the cabins in the order of boiler cabin, engine room, boiler cabin, and engine room, and any boiler cabin can provide steam for any one of the engine rooms, so as long as there is no damage to 1 boiler cabin and 1 engine room, the ship can maintain its navigational capability. Ships with all-fuel alternating power units can also adopt a similar arrangement. An earlier computational study yielded the following results:
It was important to ensure that the individual units could have true independence and not rely on a common auxiliary system. The next generation of integrated all-electric propulsion ships should be better in this regard, they will arrange multiple generators with wide spacing, and the independently arranged propulsion motors may already be able to be arranged in pods located outside the hull.
This unitary arrangement later developed into the concept of "partitioning": the frigate could have up to 5 partitions, each with independent facilities such as power supply, ventilation (to prevent smoke from spreading), water supply, cooking, and toilets. It is very difficult to achieve complete zoning of a ship, each partition needs to lay out all the key equipment needed, but even if it is only in some areas, it is already a huge step forward. Ideally, crews should live in the area where they work, so that they don't need to open the doors and hatches when they go to the war position.
The explosion of missiles hitting above the waterline and the fragments they produce can destroy a wide range of superstructures and important equipment inside those structures. Armored defenses couldn't do anything about it either: flying fish anti-ship missiles from the Falklands War could penetrate 12 inches of armor. The main way to deal with these threats is to control the scope of their destruction, but these protections can only be concentrated in the vicinity of important equipment, which the British Navy will set up backups and arrange separately. The main cable also needs to be well protected, if the main cable is combined with the structure, it can save a lot of work, so that it can resist the 99% of the fragments hitting the cable.
By the end of World War II, the effects of water ingress were the only ones that could be accurately calculated among all forms of damage. Even if there was no computer at the time, the resulting values were very close to the actual situation. Today, it only takes a click of the mouse to calculate the stability of the ship after damage, and the calculation structure is more accurate. The rest of the effects were studied by experimenting directly on older ships, which were often modified to try out various new ideas. Recognizing the dangers of asbestos, a large number of related tests had to be abandoned, only a small fraction of them were preserved, and had to be carried out at least 200 nautical miles from the coast, and the experimenters had to wear a full set of protective clothing. In 1988, the British Navy conducted an experiment called "HULVUL" on the first frigate that did not use asbestos at all. The experiment covered more than a hundred projects, including igniting a helicopter located on a flight deck. In a later test, the ship replaced half of the boiler chamber with the Type 23 power bay structure for high-yield underwater explosion tests. In the next section, we will discuss the lessons of the Falkland Islands War.
Computer simulation technology has been developing rapidly, and by the mid-1980s, the effects of explosions and fragmentation have been accurately reproduced, and vibrations and shocks can also be studied. It is not yet possible to estimate the impact of the fire very accurately, but researchers are working on it. The purpose of studying these effects was to develop a specification that would have an x% chance of maintaining a combat capability of y% when each part of the ship was hit by a 500 kg warhead.
USS Coventry near the Falkland Islands. It was hit by 3 bombs and 5 main watertight compartments were flooded, and there was no hope of survival. In a design, it is impossible to calculate the effects of large-scale asymmetric water ingress on ships without computers with powerful computing power.
There is a prominent problem here: ships can be lost due to some very simple failures, so the computer assessment must be very detailed. When the computer evaluation of a newly designed ship is carried out in sufficient detail, it may be too late for the personnel involved to make drastic changes to the design. The computer evaluation of a new vessel is divided into two phases: the first phase requires a rough analysis of key features such as the spacing of the ship's bulkheads, and the second phase requires a detailed study of the completed design of the ship. The overall design of existing ships can no longer be changed, but the relevant calculations can still provide experience for the next generation of ships.
The real problem with damage tube control is exactly what its goal is. The goal of the damage pipe is not to create an "unsinkable ship"; I think the goal of the damage control is to make the enemy's task as difficult as possible, and our ships cannot be lost by a trivial attack. Ultimately, this kind of thing is still to blame the designer: can he sleep peacefully when his work sinks to the bottom of the sea? Has he really done his best?
This article is excerpted from the History of the Development of Warship Design in the Royal Navy, Volumes 1-5 (5 volumes)
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