Taigei is the first ship of the new class. Two more are under construction. Another four are planned. They are the largest submarines built in Japan since World War II. And also the most expensive. The price for one is to be around $ 650 million (about PLN 2.5 billion). Almost half as much as older ships with traditional batteries.
However, the Japanese seem to be convinced that the new ships are worth the price. For now, they are the only ones, and the rest of the world is watching. What the Japanese are doing is a major revolution in the world of submarines. The technologies that were used on them almost from the beginning, at the turn of the 20th century, were thrown into the bin.
Two options to choose from
Submarines are currently divided into two main categories, differing in their propulsion source. Most powers build large and expensive nuclear-powered units. It is very powerful, for a virtually unlimited time and in an air-independent manner. It’s the perfect combination for submarines. However, it has disadvantages. The main ones are cost, complex technology and very difficult to obtain uranium fuel. Only in September, the Americans rejected a request from allied South Korea to provide it if the Koreans wanted to build a nuclear submarine. It was found that USA he will not pass it on to anyone, not even to his closest allies. Additionally, the reactors, turbines and all the equipment necessary for their operation is large and relatively noisy.
Faced with these problems, the world continues to do well in the second category of submarines. In Polish, they are called conventional. In English terminology, these are diesel-electric ships. Their driveline usually consists of diesel engines, which are powerful but require air to operate. So they can only be used on the surface or just below it, when the ship projects special pipes above the water, called snouts. They allow air to be drawn in and exhaust fumes to be expelled. Diesel engines are used not only to move a ship, but also to recharge large batteries. The energy from them powers additional electric motors, which enable swimming at greater depths, without access to air.
Such a system was invented as early as the end of the 19th century, although initially with gasoline engines. During World War I, diesel engines were already dominant, and it has remained so until today. Conventional ships have one major advantage, they can navigate underwater without access to air, and the whole system is reliable and quiet when using electric motors. However, they have a huge disadvantage, which is a very limited range and speed under water. It’s just that classic acid batteries are inefficient, and you can pack them into the tight interior of a submarine relatively little. So you cannot accumulate a large amount of energy for electric motors.
For example, very widespread today and considered successful Soviet / Russian Project 877 (Poland has one, ORP Orzeł). With a maximum underwater speed of 21 knots (39 km / h), they can only sail 24 kilometers on batteries. This range can be extended to more than 700 kilometers, but at the expense of a speed limit of just three knots (5.6 km / h), which is slightly slower than a marching man. As you can see, these are not dazzling possibilities.
Additionally, acid batteries can be dangerous. If water enters them, it may cause fire, explosion and production of poisonous gases. Something like that caused the loss of numerous submarines, or the death of some of their crews. Recently, the loudest incident was sinking of the Argentine ARA San Juan in 2017. The crew reported the battery fire and its containment, but then contact was cut off.
Search for something that would work
For decades, an alternative power source for submarines has been sought. One that would not be dependent on access to air. Germany during World War II, they experimented with an engine designed by Helmuth Walter that ran on hydrogen peroxide. However, it turned out to be too complicated, expensive, unreliable and dangerous. In the USSR, experiments were conducted with diesel engines powered by liquid oxygen, but also without much success.
Only in the 1990s were practically solutions developed. The Swedes included a Stirling engine in the propulsion system of their submarines. It is powered by diesel and liquid oxygen. It works in a closed circuit, emitting no fumes. The Germans, on the other hand, moved towards fuel cells in which the chemical reaction of fuel and oxidant takes place. The most common are liquid hydrogen and oxygen. The French modified the steam turbine by feeding it with ethanol and oxygen. Of these three options, the German and the Swedish ones have gained considerable popularity in the world.
The Japanese closely watched European drives and decided to buy a Swedish solution. The Soryu-type submarines, built since 2005, have Stirling engines. Thanks to them, they are to be able to swim up to 11,000 kilometers under water at a speed order 12 km / h (i.e. already running man). Years of experience with this type of solution, however, did not convince the Japanese that it is optimal. The main problem is the low power of the alternative drive, which prevents it from developing higher speeds underwater. In addition, the considerable size of the engine itself and its fuel tanks, which are usually quite exotic and cause logistical problems.
The simpler is the better
The Japanese decided that a better way would be to return to the roots, but with a modern twist. Classic acid batteries have been replaced with modern lithium-ion batteries. The ones that are currently the basis of virtually all civil handheld electronics. They are much more efficient, durable and can be recharged much faster. According to the Japanese, the ships equipped with them will have a similar range underwater as the ships with auxiliary propulsion. Additionally, they will be able to swim faster.
It was decided to pre-test the idea on the last two ships of the Soryu class, the eleventh and twelfth. While still under construction, the Stirling engine and its fuel tanks, as well as traditional batteries, were replaced with lithium-ion batteries. The ship, Oryu, has been in service since March 2020 and has been extensively tested. The Toryu is scheduled to enter service next year. However, both are treated as makeshift test platforms. Simultaneously with their construction, a seriously modified type of ships was planned and started to be built. From scratch prepared for lithium-ion batteries, with larger diesel engines enabling the use of quick-charge possibilities, and with newer electronics. These are the Taigei type ships.
The specific capabilities of ships with new batteries have not been revealed. The Japanese seem to be convinced, however, that they will be better than the previous solutions. At least when it comes to their needs. There is no doubt that this is a very expensive equipment. Lithium-ion batteries are relatively expensive, and new ships are expected to be several hundred tons. Moreover, as is well known, these types of batteries have the potential to ignite violently, releasing large amounts of heat and poisonous gases. The Japanese say that those for ships are specially reinforced, enclosed and surrounded by an efficient fire extinguishing system. Regardless, the threat remains.
Time will tell if the Japanese are right. In the armed forces and the armaments industry, this kind of revolution is approached with caution. Known, tested and refined, it is usually valued higher than new, uncertain and underdeveloped. Even if it offered, in theory, seriously improved performance. Certainly, all states and companies that create submarines will closely follow Japanese progress.
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