The Hunt for Red October - Tom Clancy [28]
"On a boomer? You put something like that on a strategic missile sub?"
"The Russkies are a funny bunch, Jack, and they design things their own way. This is the same bunch that built the Kirov class with a nuclear reactor and an oil-fired steam plant. Hmm—twin screws. The aft doors can't be for a sonar array. They'd foul the screws."
"How 'bout if they trail one screw?"
"They do that with surface ships to conserve fuel, and sometimes with their attack boats. Operating a twin-screw missile boat on one wheel would probably be tricky on this baby. The Typhoon's supposed to have handling problems, and boats that handle funny tend to be sensitive to power settings. You end up jinking around so much that you have trouble holding course. You notice how the doors converge at the stern?"
"No, I didn't."
Tyler looked up. "Damn! I should have realized it right off the bat. It's a propulsion system. You shouldn't have caught me marking papers, Jack. It turns your brain to Jell-O."
"Propulsion system?"
"We looked at this—oh, must have been twenty some years ago—when I was going to school here. We didn't do anything with it, though. It's too inefficient."
"Okay, tell me about it."
"They called it a tunnel drive. You know how out West they have lots of hydroelectric power plants? Mostly dams. The water spills onto wheels that turn generators. Now there's a few new ones that kind of turn that around. They tap into underground rivers, and the water turns impellers, and they turn the generators instead of a modified mill wheel. An impeller is like a propeller, except the water drives it instead of the other way around. There's some minor technical differences, too, but nothing major. Okay so far?
"With this design, you turn that around. You suck water in the bow and your impellers eject it out the stern, and that moves the ship." Tyler paused, frowning. "As I recall you have to have more than one per tunnel. They looked at this back in the early sixties and got to the model stage before dropping it. One of the things they discovered is that one impeller doesn't work as well as several. Some sort of back pressure thing. It was a new principle, something unexpected that cropped up. They ended up using four, I think, and it was supposed to look something like the compressor sets in a jet engine."
"Why did we drop it?" Ryan was taking rapid notes.
"Mostly efficiency. You can only get so much water down the pipes no matter how powerful your motors are. And the drive system took up a lot of room. They partially beat that with a new kind of electric induction motor, I think, but even then you'd end up with a lot of extraneous machinery inside the hull. Subs don't have that much room to spare, even this monster. The top speed limit was supposed to be about ten knots, and that just wasn't good enough, even though it did virtually eliminate cavitation sounds."
"Cavitation?"
"When you have a propeller turning in the water at high speed, you develop an area of low pressure behind the trailing edge of the blade. This can cause water to vaporize. That creates a bunch of little bubbles. They can't last long under the water pressure, and when they collapse the water rushes forward to pound against the blades. That does three things. First, it makes noise, and us sub drivers hate noise. Second, it can cause vibration, something else we don't like. The old passenger liners, for example, used to flutter several inches at the stern, all from cavitation and slippage. It takes a hell of a lot of force to vibrate a 50,000-ton ship; that kind of force breaks things. Third, it tears up the screws. The big wheels only used to last a few years. That's why back in the old days the blades were bolted onto the hub instead of being cast in one piece. The vibration is mainly a surface ship problem, and the screw degradation was eventually conquered by improved metallurgical technology.
"Now,