Whose factual errors?
The Public Affairs Office, Naval Submarine Base, Kings Bay, Georgia, agrees with Doc Nickel. DESCRIPTION OF NAVAL NUCLEAR PROPULSION PLANTS
Okay, okay, the reactor heats water that in turn through heat exchangers then heats the water that drives the turbines, and the water doesn’t actually boil, and I suppose if one wants to get technical, the turbines are more accurately labelled motors rather than engines. I’ll go sit in the corner for two tenths of a second in chastizement.
However, it’s more accurate to say the reactor crates steam which drives turbines, rather than what was insinuated in the post I was replying to- IE, the reactor crates electricity which drives the boat via large electric motors.
The rest, smaller, lighter, etc, are more or less the truth- a steam turbine of X shaft horsepower is considerably lighter and less bulky than an electric motor of an equivalent rating. Heat exchangers aren’t light or compact, but then, neither are massive banks of batteries- however, the generator sets to supply the batteries would add considerable bulk.
My own.
Oh. Sorry. 
According to Warships1 the Tang and Barbel class submarines were much faster underwater on electric motors. This is a terrific site with details about all the warships of the world.
Hmm. That site does make a point of mentioning these classes of subs were the first to use the teardrop or “albacore” hull shape, which is usually associated with nuclear subs. Obviously, MonkeyMensch was right when he said these hulls were more efficient submerged than surfaced. This is very counterintuitive, but numbers don’t lie.
Ex-submarine officer here (688-I class)…
Not much to add here, as most of the misconceptions have been addressed. I hate to let a sub thread go by, though, so I’ll add my two cents, and second some of the points that have been made.
Modern subs with teardrop-shaped hulls travel considerably faster submerged than when surfaced. (These hulls are also referred to as “Albacore” hulls after the name of the first experimental boat with this hull shape. The Nautilus was of course the first nuclear submarine, and its hull shape was similar to the old-WWII hulls. IIRC, the Skipjack was the first submarine to combine nuclear power with a teardrop-shaped hull.)
The teardrop-shaped hull is not optimized for surfaced travel. (In particular, there is no angular bow.) The inefficiency becomes so great that there is a self-imposed limit for reactor power on the surface. Near max surface speed, one could double the output of the main engines and gain a trivial increase in speed. Thus, the power limit, so as not to needlessly waste nuclear fuel.
The main engines on modern U.S. subs are steam-driven, not electric. There were a couple of trials in the past with electric drive, though, and the design may make a comeback in the future.
Oooh, oooh! robby I’m going to guess the Springfield? Do I get a prize if I’m right? Can I go out and do angles and dangles?
Sorry, not the Springfield. (I had a buddy on that boat, though.)
[sub]BTW, I was out of town for the weekend, hence the delay in replying.[/sub]
Lizard wrote,
I don’t believe this is correct. Power and energy aren’t the same thing. Given enough time, a 500-watt electic motor could have its batteries charged by a a 2-watt guy on a treadmill.
http://www.fourays.org/submarine/agosta2.htm
That’s 2686 kilowatts from the diesels (apparently using a single type of unit isn’t hip in the heady world of French Submarine Describing).
Batteries of any size could be used to power that motor. If it was a 2685 kilowatt-hour battery it would take an hour for the diesels to charge it. I’m sure most diesel-electric subs have more powerful diesels than electrics, but I don’t believe there is any physical principle dictating this.
Here is an image I hope will illustrate robby’s point about modern subs on the surface.
That’s a picture of the USS Seawolf (or maybe the Connecticut) on the surface. Notice the depressions in the surface of the water on each side abaft the bow. It is probably caused by the blunt nose of the modern hull shape - something you’d never see on a surface craft (or a pre-schnorkel submarine*). It certainly doesn’t look very efficient. As has been established, designers of modern subs don’t care much about surface movement, so it’s not a strike against this fearsome new class.
Couldn’t find any really good images of WWII-style subs since my connection is slow and I am lazy.
http://www.kriegsmarineart.com/type_viic.htm
They aren’t photos, but they look pretty true to photos I’ve seen in books of pointy-nose boats blazing along at convoy-beating speeds on their big diesels.
- And by pre-schnorkel I mean one conceived of before the potential of schnorkels was truly realized; plenty of subs were designed and built - along conventional slower-when-submerged lines - until long after the Dutch invented the schnorkel (in the early 1930s, IIRC).
My experiences with flowing steam, steam in heat exchangers, and steam turbines were that they were kind of loud. How is this dealt with? Sound insulation or parts designed to minimize noise?
The USS Tullibee (SSN 597) was a pure electric drive, it had steam driven generators that produced the electricity for the drive motors.
Indeed. USS Tullibee (SSN 597) was one of the “couple of trials” I referred to in my first post. The other was USS Glenard P. Lipscomb (SSN 685). Both boats were test platforms, and neither can be considered to be a successful design. To illustrate this point, note that both were one-of-a kind designs. (Compare this to the 62 hulls of the SSN 688 Los Angeles-class and the 37 hulls of the SSN 637 Sturgeon-class.)
Relevant quote from FAS website on USS Glenard P. Lipscomb:
Yes. 
In some cases old U-Boats actually where faster underwater that on the surface, in rough seas the surface speed was greatly reduced, so if they submerged they could actually move faster. :rolleyes:
But nominally, they didn´t have the horsepower nor the hidrodinamics to run faster underwater.
However I recall a prototype sub that used hidrogen-peroxide as fuel that could go REALLY fast underwater, although for short periods of time.
I remember seeing a small one-man sub built like a speedboat that could use its regular internal combustion engine underwater fed by its air tanks. Would carrying extra air tanks for the engines to run on given the old diesel subs greater underwater speed and range?
An otherwise “normal” U-Boat that could run it´s diesel engines underwater would be still slower when submerged because of all the drag created by the deck structures (tower, handrails, deck gun, etc)
I doubt you could carry enough air to power the diesel engine for any decent running time. You need a way to exhaust fumes, too, and having bubbles come to the top is probably pretty noisy.
Er, come to the surface.
Also, there were U-Boats that ran underwater with schnorkels. They were still slower with diesels, due to hull design.