Of course, the design index of the Jiaolong-class submarine is very high, and its performance is also the most outstanding of its time, but the submarine is originally a very complex maritime weapon platform, and the complexity of design and construction is far greater than that of the previous fast gunboats. At the same time, the value of a submarine is more than ten times that of a gunboat, and it can easily cost millions of dollars.

From a design point of view, submarines, like other ships, are the result of a compromise of various factors. However, in the process of submarine design, it is actually very difficult to compromise by taking into account various factors, due to the various contradictory conditions that the designers have to meet.

The first thing to consider is the excellent underwater performance of the submarine, and the surface performance of the submarine should also be weighed. Another trade-off to consider is the balance between the submarine's displacement, its main dimensions and the submarine's overall performance. For example, an increase in displacement can bring many benefits, such as an increase in the amount of weapons carried, an increase in fuel, and an increase in combat sustainability, but an increase in displacement must have enough power as a support, and if the power is insufficient, the performance of the submarine will drop significantly, or even outweigh the losses.

When designing a submarine, it is also necessary to ensure that the submarine has enough buoyancy to float from under the water to the surface. When the submarine is under water, the displacement of the watertight part of the submarine must be equal to the total weight of the submarine. After the submarine is dived, the basic condition for controlling the submarine is that the submarine neither sinks nor floats to the surface of the water, and it is necessary to maintain a balanced state, and the slight ups and downs that occur during underwater navigation are controlled by horizontal rudders and thrusters, and it is not easy to do this.

Another difficulty of submarines is that submarines are ships that sail underwater, so it needs to withstand the huge pressure of seawater, and the deeper the submarine, the greater the diving depth. The more difficult it is to design and build. Volume is a fundamental parameter of submarine design, which begins with a prediction of the required interior space, and the pressure-resistant hull effectively encapsulates these volumes. Reducing the weight of the submarine did not reduce the displacement of the submarine, this is due to the fact that the space in the body of the pressure-resistant boat was practically not reduced, and the submarine could dive to great depths. Until the load on its pressure-resistant hull reaches a critical state.

The power plant on the submarine is highly weight-intensive, and the battery usually accounts for a large proportion of the weight, and also occupies a large amount of internal volume. Therefore, the weight and volume of these power units should be reduced as much as possible in the design to ensure that the submarine has enough buoyancy and will not sink.

All of this is a completely new subject for the Dragon Soul Ordnance Complex. At Xiao Weiguo's suggestion, the design team chose a cigar-shaped hull design. This is a very advanced design, which should have appeared after World War II, and the pre-World War II submarine designs were all ship-type. Of course, from the principle of mechanics, the ideal pressure-resistant hull should be a spherical structure, because the spherical structure is the strongest shape, but its internal volume is limited, and the strength becomes very low when the diameter is too large. So it is not suitable for submarines with a displacement of several hundred tons, thousands of tons.

So the cigar-shaped pressure-resistant hull of the Dragon Soul Ordnance Complex. It's a compromise. It is cylindrical in the middle, hemispherical in the bow and conical in the stern. It is a good shape both in terms of mechanical principles and underwater hydrodynamics. The reason why Xiao Weiguo did not have the best teardrop-shaped hull was because the materials and technology at this time did not meet the requirements.

The Jiaolong-class submarines are designed to dive to a depth of 150 meters. This is a high indicator. Because submarines at this time generally do not dive deeper than 100 meters.

From the perspective of the overall arrangement of the submarine, the internal space provided by the pressure-resistant hull of the submarine with a circular cross-section is a space that is difficult to deal with effectively, and it is difficult to make full use of it. There were designers who used elliptical cross-section submarine pressure-resistant hulls. But the intensity was not enough to fail. Later, during World War II, the XXI submarine of the German Construction Bank adopted a figure-8 cross-section, so that the increased volume was used to carry more batteries and improve the underwater endurance and speed. However, such a shape obviously has a great price to pay in terms of resistance, and in fact, the gains outweigh the losses. So Xiao Weiguo did not adopt this design.

In the selection of submarine hull structure, Jiaolong-class submarines adopt a double-hull structure. From the perspective of the three hull structure forms, the double-hull structure has obvious advantages. Compared with the other two structures, the single-hull structure is characterized by the small size of the submarine and the small surface area of the hull, so the resistance when navigating underwater is less. However, because the single-hull submarine is arranged with ballast water tanks in the pressure-resistant hull, the effective volume in the boat is much smaller.

The design of the double-hull submarine was proposed by the French submarine designer Maxim in 1896. At that time, submarines of this double-hull structure were called submersible ships, and it spent most of its time on the surface, diving only when the target appeared. On a submarine with a double-hull structure, there is also a lightweight, non-pressure-resistant hull on the outside of the pressure-resistant hull, which is often referred to as a light hull. The space between the light hull and the pressure-resistant hull is used as ballast water tanks, fuel tanks, and sometimes even for loading weapons, so as to provide reserve buoyancy for the submarine and increase the endurance and combat effectiveness of the submarine.

At this time, the reserve buoyancy of single-hull submarines was only about 10 percent, while the reserve buoyancy of double-hull submarines was as high as 30 percent. In addition, the double-hull submarine also has an excellent hull shape, the Soviet submarine designers are very willing to use the double-hull structure, this is because the Soviet submarine often sails in the cold and frozen seas, the single-hull structure submarine may be damaged once it collides with the ice, and the double-hull structure can play a protective role, in addition to the double-hull submarine in the attack, can also play a good role in protection.

Because Sweden and the Soviet Union are adjacent to each other, the submarine activity area of the Swedish Navy is similar to that of Soviet submarines, so the choice of double-hull submarines is also a consideration for the conditions of use, as well as for safety. In addition, Xiao Weiguo's Jiaolong-class submarine plan is borrowed from China's Ming-class submarine design, and China's conventional submarines are basically learned from the Soviet Union, all of which use double-hull structures, and it can be seen from the drainage holes outside the submarines that Chinese and Soviet submarines are double-hulled. In the early days, Germany also used a double-hull structure, but after the war, it was changed to a single-hull structure, of course, as the equipment on the submarine became more and more complex.

Therefore, now the Jiaolong-class submarine chooses a double-hull structure, which should be a very reasonable design. (To be continued.) )