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Era of anaerobic submarines with new type of batteries is coming

This post was published in Nezavisimaya Gazeta. The point of view expressed in this article is authorial and do not necessarily reflect BM`s editorial stance.

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MOSCOW, (BM) – Scientific and technological progress is preparing us for another revolution in the field of naval weapons: in the foreseeable future, the classic diesel-electric submarine will be replaced by submarines with so-called anaerobic or “air-independent” power plants (VNEU).

However, it is not yet possible to say exactly what they will be due to the ongoing competition of ideas. And also due to the different approaches to financing R&D and the construction of experimental vessels adopted by the leading maritime powers.

Disadvantages of the classics

What’s wrong with a classic diesel-electric submarine (diesel-electric submarine)? And the fact that it is not “underwater“, but “diving”. Indeed, to charge the batteries that feed the underwater propulsion motor (and on modern submarines it also provides movement on the surface), a diesel generator is used, which requires atmospheric air to operate.

Floating to the surface to recharge the battery, the submarine becomes a target for surface ships and enemy aircraft. Ascent and dive processes are accompanied by strong noise, which is easily detected by sonar devices. In addition, the submarine on the surface is visible to radars, not to mention the means of species reconnaissance. Even the appearance of the so-called snorkel device (also known as the RDP: the device for operating a diesel engine under water) and electric boats (diesel-electric submarines with increased battery capacity) did not save the “wolf packs” of Grand Admiral Karl Dönitz from defeat in World War II.

Today, the most technologically advanced domestic diesel-electric submarines, for example Project 677 “Lada”, can spend no more than 9-10 days under water and travel up to 650 miles at a low economic speed (3-4 knots). This circumstance gave the critics of the project, including the then (2007-2012) Commander-in-Chief of the Russian Navy, Admiral Vysotsky, the right to speak of diesel-electric submarines (in general and in particular) as “brains and weapons” sitting on the “energy of the Second World War.”

Vladimir Sergeevich is wrong: the first diesel-electric submarines are considered the French Z built in 1905 and the Russian “Lamprey”, launched in 1908. In a word, diesel-electric submarines have been in operation for 115 years and their serial construction continues. On the same “frets” there is a total order of the Ministry of Defense of the Russian Federation for six ships, of which only two are ready so far.

Do not offer an atom

In parallel with them, Russia has been actively building nuclear cruisers with steam generating units (PPU) based on a nuclear reactor for more than 65 years. They have a cruising range, limited only by the endurance of the crew, a supply of food and essentials to ensure life on board.

In fact, an atomic PPU is an anaerobic power plant. However, this circumstance is usually ignored in general considerations both on the pages of the press and even in the internal documents of shipbuilders and government agencies. Instead, under the term “VNEU” only solutions that are not related to the physics of nuclear fission are considered. The reason is that many countries, for political and other reasons, do not want to get involved with nuclear energy and weapons. Placing such on a ship inevitably leads to a large dimension, high cost of construction and maintenance, which is unacceptable for many countries of the world for financial and other reasons.

The export of nuclear-powered ships is complicated by the existing agreements of the superpowers. Therefore, the project 670 submarine was leased, and not sold to India, where it was used during 1988-1991 under the designation S-71 Chakra. Today, Indian sailors have at their disposal the S-72 project 971I submarine, which was taken in 2012 on a 10-year lease.

So far, these two examples are the only ones in the world where a nuclear fission-based submarine built by one country was transferred for operation to another state. This fact once again confirms the special relationship of strategic partnership that has developed between Russia and India.

Indian competition

Meanwhile, the same India is holding an international competition for six non-nuclear submarines with VNEU with the right to order additional orders for the same quantity at the previously agreed contract value. According to local sources, a request for proposal (RFI) is expected to be sent the other day.

According to the terms of the corresponding tender 75I, the basic project must be proposed by a foreign participant who has already built and commissioned a prototype submarine, which is suitable in terms of parameters as an initial platform for creating a certain Indian version.

The competition is being held by the Indian military department, among the invited participants are companies from Russia, Germany and France. Sometimes Sweden, Spain and even Japan are also ranked among them. However, according to the information we have from Indian sources, firms in these countries either refused to respond to requests from Delhi, or cannot satisfy them on the merits.

The above list of states where work is underway on “non-nuclear” VNEU is far from complete. In our case, it is artificially limited by Indian specialists. And they carefully studied the issue and turned only to those who have made good progress in solving issues, have knowledge and skills and are ready to share them for a fee.

The requirement for the mandatory inclusion of VNEU in the list of systems of the future submarine of the Indian fleet significantly increases the technical risks of the implementation of the corresponding project. Analysis shows that none of the known types of anaerobic installations are ideal in every way, each has its own advantages and disadvantages. In addition, shipbuilders need to take into account the peculiarities of geographic zones, basing conditions and the level of training of the fleet personnel of the main customer and foreign customers.

German way

The German company Howaldtswerke-Deutsche Werft (HDW) from the ThyssenKrupp Marine System concern has advanced farthest to meet the needs of the fleet of its country and its closest allies in the NATO bloc. She built (1998–2017) a series of 10 type 212A submarines with VNEU based on the so-called fuel cells with intermetallic hydrogen storage. Six are operated by Germany, the rest by Italy.

During acceptance tests, the U-32 submarine of the German naval forces demonstrated the possibility of continuous underwater navigation for 18 days, and also covered a distance of 2,800 km (1,512 miles) without surfacing. These are quite high figures, and they are actively used by the Germans as proof of the correctness of their path.

The anaerobic power plant chosen by the German shipbuilders is built on the basis of an electric power generation system using fuel cells. Research on them has been going on for more than half a century, and in the USSR they were considered both for submarines and space ships. As a rule, we are talking about alkaline, but there are others: for example, Indian scientists are experimenting with phosphoric acid.

Let’s pay tribute to the developers of type 212A: they managed to go a long way from theoretical and experimental research to the practical implementation of their ideas in metal. Only between the moments of the first launch of the experimental VNEU and the delivery of the finished submarine to the fleet passed a quarter of a century!

The European Union authorities helped to achieve the result HDW, which financed long-term programs of science and industry for the introduction of hydrogen energy in road and sea transport. Since the mid-70s of the last century, activities in the field of hydrogen fuel, including the storage and transportation of hydrogen, have been carried out by many European companies, primarily auto giants. Then, after the formation of the EU, this direction was actively supported and financed by pan-European structures, which helped to attract additional commercial investments.

One way or another, HDW specialists managed to bring a submarine with a well-functioning VNEU to the international market. It provides low noise when driving under water, low temperatures of the power plant, and emissions are reduced only to the discharge of ordinary water obtained as a result of a chemical reaction on board.

Problematic moments

At the same time, the German power plant has problematic moments. First, there is great technical complexity and high cost. Secondly, it is an addition to the existing energy of the classic diesel-electric submarine and, accordingly, entails a significant increase in the size of the ship. Submarines of type 212A are more than three times larger than those that replaced in the German fleet – type 206. Thus, the total displacement is 1840 tons against 500 tons.

Thirdly, the anaerobic installation proposed by HDW requires a long study of the material by the submarine crew and coastal services, as well as the construction of the necessary coastal infrastructure.

The biggest problem with the proposed HDW solution is considered to be the so-called intermetallic hydrogen storage. The hydrogen metal hydride used in Type 212A submarines provides a high level of crew safety, but causes an increase in volume and weight. With a large specific gravity of the metal hydride alloy, the hydrogen content in it is very low. For this reason, shipbuilders have to make numerous compromises, trying to provide the required tactical characteristics of the boat with a significant mass of metal hydride transported by it. Among them – a decrease in ammunition to 12 torpedoes (versus 18 on Russian and French diesel-electric submarines).

The next problematic point is the applicability of the proposed HDW power plant in various climatic zones, primarily in the north and in the tropics. The work of the German system in the warm waters of the Indian Ocean seems to be especially difficult.

High seawater temperature can spontaneously increase the temperature of the metal hydride at the very moment when the process of hydrogen evolution is in progress. It itself is accompanied by an increase in the temperature of the alloy. Accordingly, there is a risk of inadvertent release of additional hydrogen in excess of the required measure. And in the north, the cold seawater can, on the contrary, reduce the amount of hydrogen released below the required level.

Optimized for NATO

HDW has optimized the parameters of the energy system of the 212A submarines for operation in the Baltic and North Seas in accordance with the operational plans of its own country’s fleet. When negotiations began with Italy, the project had to be changed taking into account the climatic conditions of the Mediterranean Sea.

It should be remembered, however, that the fleets of the European NATO member countries are operated near the coast where the North Atlantic bloc has full control over the use of air and sea space. Accordingly, divers can safely swim in and use diesel generators to recharge their batteries, and use fuel cells only when absolutely necessary. This practice is evidenced by the analysis of the exercises conducted within the framework of the interaction of the military of the NATO bloc.

As part of the deployment of a grouping of German-type submarines, the countries of the North Atlantic Treaty have erected and are operating numerous hydrogen infrastructure facilities. They are engaged in the production of this fuel with a given degree of purity, as well as the means for storing it and delivering it to specially designated naval bases. It should be noted that the construction of such a coastal infrastructure was an important part of the international program within the framework of bloc solidarity.

Export type 214

Having decided to launch a large-scale project to introduce non-nuclear submarines with an additional power plant based on fuel cells and intermetallic hydrogen storage, HDW initially counted on export. Otherwise, it would not have been possible to return the invested own funds and commercial investments.

Therefore, having created a type 212A under the requirements of their own fleet, the firms began work on the export version. It was type 214, characterized by increased dimensions: the length increased from 56 to 65 m.

According to the developer, type 214 was created primarily for customers among NATO countries: Portugal (a couple of boats were delivered), Greece (four were delivered, two more are under construction), Turkey (assembly of six under license). However, there is another explanation: the initial project turned out to be unpromising for further development. Especially considering the emergence of new types of missile and torpedo weapons: they simply did not have enough space.

Meanwhile, the technical feasibility of integrating it on board in the future has become critical to maintaining HDW’s position in the global market as a strong rival emerges for its products. First of all, Russian diesel-electric submarines of the Varshavyanka family in versions of the 877EKM project (for India) and 636M (for China), which differed from the previous ones by the installation of the most powerful Club-S missile system.

Marketing studies have shown that the German submarine, which is difficult to build and operate, and is also demanding on coastal infrastructure, has low chances in Southeast Asia. To date, it has been “registered” only in South Korea, where a program for the acquisition and assembly of nine buildings is being implemented. Low demand in the region is due to the lack of expensive European-style hydrogen infrastructure, which will take decades to deploy. Besides, why buy a German “goldfish” if it also turns out to be “unarmed” in the face of improved Russian “Varshavyanka” (projects 636.1 and 636.3), not to mention the new generation embodied in the design of “Lada”.

Competitive friends from France

For all the ostentatious “European solidarity” between the countries of the Old World, there is tough competition. In addition to Russian shipbuilders, French and Swedish shipbuilders are gladly ready to move HDW on the global market.

So, much less technically complex, but better armed “Scorpion” (classic diesel-electric submarine in modern French performance) bypassed the Germans in competitions in India, Malaysia, Chile and Brazil. Among other things, this showed that it is too early to write off a submarine of the traditional scheme for scrap. Moreover, when there are simple solutions to slightly increase its autonomy. By the way, the basic version is capable of passing 550 miles under water at a speed of 4 knots – much worse than the test result of the U-32.

Carrying out active marketing of the “export-oriented” project “Scorpen” (only nuclear submarines are in service with the French Navy), designed for countries that in the future want to get hold of diesel-electric submarines from VNEU, the French were sometimes very cunning. They, in particular, proposed as an option the installation of an additional compartment with a VNEU of a very exotic type – MESMA, which is a closed cycle steam turbine that consumes ethanol and oxygen.

However, this type of anaerobic installation has found application only on experimental ships and prototypes of “sabotage” boats. The energy efficiency is extremely low, but according to formal criteria, MESMA quite fit the definition of VNEU. They bought it in India, when they carried out an international tender for Project 75. As a result, we got: the planned construction timeframe for a series of six Kalvari boats (modification of the Skorpen) could not be met even though in fact none of them was equipped with VNEU will be. The parameters of those that can be installed in the additional compartment by cutting it into the center of the boat’s hull of this project turned out to be too low.

In an effort to reassure their Indian partners, who were frankly upset about the progress of the practical implementation of Project 75, six years ago the French informed them about the development of a second-generation fuel cell intended for use in a promising anaerobic plant based on diesel fuel reforming. If you cut in a compartment with a similar VNEU during the overhaul, the Kalvari’s underwater autonomy will increase to three weeks. It has not yet been possible to interest the client with a new plan: the Indians are counting primarily on a similar installation, developed by specialists from the Naval Systems Laboratory, which is part of the Ministry of Defense.

We break – the Swedes bend.

The Swedes proposed and practically implemented a project to introduce an anaerobic plant based on Stirling engines as an addition to a battery with a propeller electric motor. They consume diesel fuel and liquid oxygen, and the exhaust is easily emitted overboard at shallow and medium depths (while acting as a kind of unmasking sign if the enemy has the proper sensor equipment). In fact, this system became the first VNEU to achieve combat readiness at the turn of the century. Today it is used on submarines of the Swedish, Singapore, Japanese and Chinese navies.

Swedish submarines of the “Gotland” type (three were built in 1992-1998) with an underwater displacement of about 1600 tons have an underwater autonomy of up to two weeks. Low noise is considered the strength of Stirling engines. It is smaller than that of diesel generators for diesel-electric submarines, which gives a certain tactical advantage when charging batteries. And the compactness allowed the Swedes to build boats of relatively small displacement.

Size matters for the small and shallow Baltic Sea with its heavy commercial shipping. Since similar conditions are observed in the Strait of Malacca, Singapore decided to purchase a pair of old Swedish Westerjötland-class submarines, which were overhauled with the installation of Stirling engines, and the purchase of a batch of new construction.

But the Japanese, having spent a lot of time on improving the engine images acquired from Sweden and creating their own, recently abandoned their further development. The fact is that they build submarines of a much larger displacement (over 4 thousand tons), which required not two, but four Stirling engines to ensure an acceptable underwater speed. Attempts to create motors of this type with increased power with the possibility of using them as a single power plant ended in failure.

Perspective

Instead of using Stirling engines on submarines of the Soryu family, the Japanese from the 11th corps decided to replace the lead-acid battery with a capsule-type battery of the “ion-lithium” type that does not emit hydrogen as a by-product. In a word, the SS511 Oryu submarine, which was put into service in March 2020, is a classic diesel-electric submarine – and at the same time the first in the world with a lithium battery. Due to the increased capacity of the battery by one and a half times, as well as its better properties in charge and discharge currents, the new boat has tactical characteristics no worse than those of the previous ones with VNEU.

The domestic fleet is planning to follow the same path, already operating batteries of a new type on special-purpose underwater equipment. According to the estimates of specialists from the Rubin Central Design Bureau for Mechanical Engineering, the installation of the ion-lithium battery will increase the time of continuous swimming under water without surfacing from 9-10 to 13-15 days.

Technically, the appearance of lithium batteries in the fleet does not cancel VNEU. Therefore, many fleets of the world, including the domestic one, continue to work on both the first and second directions. Their efforts are focusing on new ways of producing and storing hydrogen, which is needed to generate electricity from fuel cells. What kind of work is being carried out, we will tell you in subsequent publications.

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