Pump jets are quieter and more efficient at higher speeds than traditional submarine screws. They do have a lower propulsive-efficiency at lower speeds compared to a traditional propeller. Pumpjets work very well at speeds above 30 kts for small speed-boats and medium-weight torpedos. They are only known to be used on nuclear submarines. Pump jets are known to “have a tactical advantage” over traditional submarine screw, which is assumed to mean acoustic advantages.
Pump Jets give a lower dived endurance, dived range, indescretion ratio, endurance. Flow separation is the primary cause of the low efficiency at low speeds by creating unsteady eddies and vortices. The inefficiencies of a pump jet over a conventional screw decrease as hotel loads increase. The pumpjet may have variations of rotors and stators that propel and straighten the flow, but regardless of the design, you want to minimize the gap between the blades and the duct. The stator may be placed in front of the blades.
There are more blades in a pump jet than a skew-back propeller, but the number of blades are still prime numbers. If there are multiple rotors, then each of the rotors have different blade numbers.
[[Acoustic Advantages of Pump Jets]]
[[Efficiency Disadvantages of Pump Jets]]
[[Ross Ireland]] – marine modeling of pumpjets
[[Hydrodynamics]] – foundational to pumpjet development
[[Turbomacchinery]] – also foundational to pumpjets
[[Shortfin Barracuda Block 1A]] – Submarine with a Pump Jet
[[Flow Separation]]
[[MK 48 MOD 6AT Propulsion System]] – uses a pumpjet
[[Virginia Class Submarine]] – uses a pumpjet
[[Seawolf Class Submarine]] – has a pumpjet
[[Suffren Class SSN]]
[[Shortfin Barracuda Block 1A]]
[[BOREI-I Class]] – also use a pumpjet
[[Shrouded Screw]] – similar but not identical
[[Poseidon Torpedo]] – uses a pumpjet
Sources
- [1] H I Sutton, Top 5 SSK Submarines and Other Questions, (Aug. 17, 2021). Accessed: Nov. 28, 2022. [Online Video]. Available: https://www.youtube.com/watch?v=qWeg7OCGw4Y
- [2] A. Morrison, “A comparison of pumpjets and propellers for non-nuclear submarine propulsion”.
Backlinks
[[Alrosa]]
[[Electric torpedoes]]
Hotel Loads
Nuclear-Powered Submarines