Diagram 1. (Courtesy sourmasov(dot)eu) indicates the openings of the the starboard impeller tunnel in a Kilo 877's or 636's light hull.
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From two Anonymous sources, early April 2018, propulsion information for Kilo submarines have been put together. Kilos are equipped with a main propulsion propeller served by one main propulsion motor of around 5.5 MW up to 500 rpm.
At high speeds, the main propulsion motor is connected to the shaft. The shaft speed (propeller speed) is reduced by the main propulsion motor’s reduction gear (eg. max speed of 500 rpm is significantly higher than propeller speed, eg. max speed 250 rpm).
At very low speeds (perhaps less than 3 knots) <3 knots="" nbsp="" span="">the main propulsion motor is not connected to the shaft and the main propeller is driven only by a small ("Economical Prop Motor in Diagram 2.) propulsion motor to achieve "economical" (less battery use) and silent operation.3>
Kilos (both the 877s and 636s) also use two small pump impellers (can also be called internal thrusters but for submarine) in two tunnels (see the two diagrams below especially Diagram 2.). These can be for:
At very low speeds (perhaps less than 3 knots) <3 knots="" nbsp="" span="">the main propulsion motor is not connected to the shaft and the main propeller is driven only by a small ("Economical Prop Motor in Diagram 2.) propulsion motor to achieve "economical" (less battery use) and silent operation.3>
Kilos (both the 877s and 636s) also use two small pump impellers (can also be called internal thrusters but for submarine) in two tunnels (see the two diagrams below especially Diagram 2.). These can be for:
i) for very low speed manoeuvring,
ii) or staying still in a current (eg. while releasing or retrieving special forces divers).
The pump impellers are set inside tunnels in the Kilo submarines light, external, hull. Kilo submarines have a double hull structure consisting of the external light hull and the inner pressure hull.
It is not known how common pump impellers are in Western and Northeast Asian (Japanese, South Korean and Chinese) submarines.
As reduction gear vibrates at high speed, the Improved Kilo 636.3 (built only for the Russian Navy) seems to have a louder acoustic fingerprint than more modern submarines (designed by TKMS, Naval Group, KHI-MHI or Saab) driven by PSMS or DC motor without reduction gear.
The Kilo appears to be too old in many respects and a new Russian conventional submarine design with modern technologies such as PSMS, AIP, LIBs and higher power diesels is needed. However with most of Russia’s submarine design budget going to Russia’s nuclear propelled submarines there is insufficient money to bring Russian conventional submarines up to Western or Northeast Asian standards.
Anonymouses and Pete