China Claims ‘Rim-Driven Thrusters’ will Make its New Nuclear Attack Subs the Best

By | Jun 05, 2017 09:32 AM EDT
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Voith rim-driven thrusters. (Photo : Voith)

Chinese state-controlled media is hyping the Chinese version of a western invention called a "rim-driven thruster" as the engine that will make the new nuclear powered attack submarines (SSNs) of the People's Liberation Army Navy (PLAN) the best on the planet.

Chinese engineers are reported to be planning a rim-driven thruster specifically being developed as an auxiliary propulsion unit for the PLAN's new Type 095 SSNs now under development. There are unconfirmed reports the first of the Type 095 boats is under construction.

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PLAN plans to build five of these boats.

Sources in the PLAN were quoted by Chinese media as saying the Type 095 will be the first in the world to use an electrically-powered rim-driven thruster, whose main advantage over traditional propulsion systems consisting of a propeller or propellers linked to a shaft is its low noise emissions.

The main disadvantage of rim-driven thrusters, however, is their reduced efficiency. This means they're unable to develop high underwater speeds compared to traditional propellers. Cavitation, which increases the noise generated by propellers, is another problem associated with rim-driven thrusters.

Rim-driven thrusters are relatively new, having been introduced only in 2010 by the German firm Voith GmbH and the Dutch firm Van der Velden Marine Systems B.V. They're intended for use as maneuvering units and not as main propulsion units.

Despite these disadvantages, rim-driven thrusters are reported to have found favor with the PLAN and are being championed by Rear Admiral Ma Weiming.

A rim-driven thruster is a marine propeller that doesn't need a hub for transmission of the driving torque. Conventional propellers need a shaft line driven by a turbine; a diesel engine or an electric motor.

The blades of a rim-driven thruster are mounted on a ring, which constitutes the rotor of an electric motor. It's surrounded by a ring-shaped stator that creates the necessary torque.  Rotor and stator are water tight and the whole unit operates submerged.

 Adm. Ma is responsible for developing multiple Chinese naval electromagnetic programs, including the electromagnetic catapult and railguns, said Chinese state-owned TV.

He revealed the PLAN is outfitting the Type 095 with a "shaftless" rim-driven pumpjet, or a rim-driven thruster.

In the Chinese version, a rim-driven pumpjet has a ring-shaped electrical motor inside the pumpjet shroud. The motor turns the vane rotor whose fan blades are attached to a rotating band built on a cylinder interior, as opposed to a propeller shaft inside the pumpjet cavity to create thrust.

Adm. Ma said that removing the propeller shaft and reducing the number of moving parts decreases the noise made by the pumpjet. Rim driven pumpjets are allegedly easier to maintain.

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