This question has been bugging me for a while now, everyone keeps mentioning that turbo-electric propulsion (as used on SSN-685 and French nukes) is somehow inherently quieter than conventional steamturbines. Why is that? Even a turbo-electric sub would need turbines to generate the electricity for the e-motor, wouldn’t it? Is the advantage based solely on the possibility of using batteries like a diesel-electric submarine and taking the turbine/generator offline during silent running?
By: Arabella-Cox - 4th October 2005 at 22:22
Yep, none of the French designs (officially) exceed 25knots. That’s still quite an achievement with respect to le Triomphant, the much smaller SSN-685 only managed 23 IIRC.
Did some research into the French propulsion systems and have found out (with my limited French!) that SNA Barracuda will have a hybrid turbo-electric/geared turbine plant! The e-motor will be used for silent running at low speed, with the turbines being connected to the shaft via reduction gear for higher speeds.
Interestingly this is exactly the same arrangement used on Britain’s Valliant class almost 40 years ago (although the equipment raft will probably stay insulated at all speeds, I’d expect).
I also learned that le Triomphant apparently features a spherical bow sonar, few sources seem to mention this.
By: hallo84 - 3rd October 2005 at 22:46
Many compromise but it all depends on the Tactics being deployed. Over all French Subs use a standard but compact design pressurised water nuclear reactor. They do not require high speeds only 25 knot.
By: Arabella-Cox - 3rd October 2005 at 15:16
Ah, the reduction gear of course, thanks! Makes you wonder what compromises (if any) the French made to develop this system to maturity when the US failed. Curiously enough the Russians don’t seem to have even tried (correct me if I’m wrong).
By: rickusn - 3rd October 2005 at 03:35
Im not an expert.
But if I remeber correctly it has to do with the noise generated by the reduction gears and the shaft.
The turbine and generator can be well isolated from radiating noise outside the ship if I remember correctly.
Heres a snippet repeated over and over:
“While this design is quieter, it is heavier and larger than conventional drive trains. Those disadvantages, along with reliability issues led to the decision not to utilize this design on a wide scale.”
Heres an excerpt and a link to a pertinent article:
“Two nuclear-powered submarines of the 1960s and 1970s, USS Tullibee and USS Glenard P. Lipscomb, also used turbo-electric drive for certain purposes –primarily to achieve quieting for ASW (antisubmarine warfare) missions. Both boats were somewhat under-powered in comparison with their contemporaries, though, and the carbon brushes of their direct-current, mechanically commutated propulsion motors created recurring maintenance problems. For that reason, the Lipscomb was retired early. Meanwhile, the rest of the submarine force retained geared turbines.”
http://www.navyleague.org/seapower_mag/july2001/ips_advantage.htm
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October 3, 2005 at 3:02 am