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Project 661 Anchar / Papa - Design

This pilot high speed nuclear submarine of 661 project is a unique submarine which had no analogs in world shipbuilding. In fact a new industry branch was established to create the first soviet nuclear submarine with a hull from Titanium alloy. The ship was built at Sevmash during 6 years. In 1969 it was delivered in pilot operation, in 1971 it obtained record underwater speed of 44.7 knots [according to Sevmash]. Due to high cost of building and exclusive combat features it was called "Goldfish" ("Zolotaya Rybka").

Designers considered three alternative materials for the manufacture of the hull - steel, aluminum or titanium. They chose titanium, although there was no base for its production - it was created simultaneously with the construction of the boat. Titanium is anti-corrosion, low-magnetic and very durable. The light hull of the boat had a circular cross-sectional shape with the aft end of the split feed type with propellers spaced apart by 5 meters (later a similar arrangement of the screws was taken on the 949 and 949A boats). In the navy, such a scheme was called "pants". The bow of the submarine consisted of two cylinders with a diameter of 5.5 m each. They were located one above the other so that in the section they represented the figure eight. The upper cylinder is the first compartment, the lower cylinder is the second compartment.

At speeds above 35 knots, due to the turbulent nature of the flow around the boat, noise arose, reaching up to 100 decibels in the boats central station. Such noise not only drove the crews mind, but also deprived the boat of secrecy. But this, in fact, was the only drawback of the secret wonder-ship.

The SSGN of the project 661 had a two-hull architecture. Durable hull, made of titanium alloy, was divided into nine compartments. The stern end of the boat was made bifurcated in the form of two axially symmetric conical shafts of shafts with a distance of about 5 m between them (in common use this decision was called "pants"). Hydrodynamic optimization of the shape of the aft tip was achieved due to its elongation with small angles of the waterline in the diametral plane and the use of elongated propeller shafts with fairings that allow the installation of propellers of optimal diameter for a given rotational speed.

A ducted or shrouded propeller is a rotating blade system that operates in a close-fitting casing or shroud. The inflow may be accelerated or decelerated by the shroud. The system in which the flow is accelerated at the rotating blades is normally called a Kort nozzle. The system where the duct decelerates the flow at the blades is normally called a pumpjet. A water jet consists of a propeller enclosed in a long duct so that little or no circulation is generated around the duct. Propulsor design is a highly specialized field, requiring high-speed electronic computers for the more sophisticated methods. Even slight cavitation noise in generally not acceptable since it immediately produces troublesome self noise.

By the early 1950s, interest by the U.S. Navy in the possible application of shrouded propellers to various types of naval vessels for the purpose of delaying cavitation and propeller noise led to studies of the theory of such a propulsion system. By the 1980s, shrouded propellers, involving fitting a ring nozzle around a propeller were commonly been used for vessels in order to improve the thrust. An accelerating shroud can accelerate the fluid ahead of the propeller to provide more efficient propeller operation at low forward velocities. Decelerating nozzles or pump jets can cause the fluid velocities to decrease ahead of the propeller and prevent propeller cavitation at high forward velocities.

A considerable drawback of such shrouded propellers is their tendency to get blocked in ice conditions, when big ice chunks hit the nozzle, stop in front of it and prevent the water flow to the propeller. Hereby the thrust of the propeller is decreased and big strains are acting on the screw blades, the axle and the bearings. Various different arrangements exist in connection with shrouded propellers, by means of which it has been tried to prevent ice from entering the nozzle. For example, grid constructions have been applied in front of the propeller. Such propeller guards prevent big chunks from entering the nozzle together with the water flow. A drawback is, however, that the grids are rather close each other in order to achieve appropriate operation, whereby the flow resistance is increased and the efficiency of the propulsion is impaired. The grid constructions also have a tendency to get blocked by ice sludge. Protective fins were arranded in front of the shrouded propeller so, that the fins are rigidly attached at their one end to the hull of the vessel and, at their opposite end, to the nozzle. A drawback is hereby the big flow resistance of the fins. When the fins are oriented to form a big angle relative to the direction of the water flow, ice chunks have a tendency to get jammed and block the shrouded propeller.

The overall performance of a submarine is often limited not by the engine but by the amount of power which can be converted to thrust within the limitation of propeller size, propeller efficiency and noise produced. All three factors are strongly related to the strength of the vortices generated at the tips of propeller blades. By obvious reasons, the propeller size is often limited in practice. The higher the power level relative to the propeller diameter the stronger the vortices, efficiency is sacrificed and noise levels are raised. With this respect, the performance can be improved by enclosing the propeller in a shroud. Shrouds tend to disperse the tip vortices, but the vortices reform at virtually full strength some distance downstream from the propeller plane, limiting the benefits of the shrouds. Structural weight, manufacturing costs and a frictional drag penalty are other consideration limiting a widespread application of shrouds.

The speed of the submarine was set at 44.7 knots (more than 80 km / h), which is still an absolute world record for submarines. At such speeds, phenomena that have not yet been observed on the submarine were found at a speed of more than 35 knots, external hydrodynamic noise created by the turbulent flow around the submarine hull appeared, and its level reached 100 decibels in the central post of the boat. For his speed, the boat was really liked the Commander-in-Chief of the USSR Navy, Admiral SG Gorshkov. (Submarine of Project 661 Anchar K-222 is listed in the Guinness Book of Records as the fastest submarine in the world. This achievement has not been surpassed so far anywhere in the world.)

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Page last modified: 16-05-2019 18:50:55 ZULU