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, this tunnel drive system avoids the cavitation problem. You still have cavitation, but the noise from it is mainly lost in the tunnels. That makes good sense. The problem is that you can’t generate much speed without making the tunnels too wide to be practical. While one team was working on this, another was working on improved screw designs. Your typical sub screw today is pretty large, so it can turn more slowly for a given speed. The slower the turning speed, the less cavitation you get. The problem is also mitigated by depth. A few hundred feet down, the higher water pressure retards bubble formation.’
‘Then why don’t the Soviets copy our screw designs?’
‘Several reasons, probably. You design a screw for a specific hull and engine combination, so copying ours wouldn’t automatically work for them. A lot of this work is still empirical, too. There’s a lot of trial and error in this. It’s a lot harder, say, than designing an airfoil, because the blade cross-section changes radically from one point to another. I suppose another reason is that their metallurgical technology isn’t as good as ours – same reason that their jet and rocket engines are less efficient. These new designs place great value on high-strength alloys. It’s a narrow specialty, and I only know the generalities.’
‘Okay, you say that this is a silent propulsion system, and it has a top speed limit of ten knots?’ Ryan wanted to be clear on this.
‘Ballpark figure. I’d have to do some computer modelling to tighten that up. We probably still have the data laying around at the Taylor Laboratory.’ Tyler referred to the Sea Systems Command design facility on the north side of the Severn River. ‘Probably still classified, and I’d have to take it with a big grain of salt.’
‘How come?’
‘All this work was done twenty years ago. They only got up to fifteen-foot models – pretty small for this sort of thing. Remember that they had already stumbled across one new principle, that back-pressure thing. There might have been more out there. I expect they tried some computer models, but even if they did, mathematical modelling techniques back then were dirt-simple. To duplicate this today I’d have to have the old data and programs from Taylor, check it all over, then draft a new program based on this configuration.’ He tapped the photographs. ‘Once that was done, I’d need access to a big league mainframe computer to run it.’
‘But you could do it?’
‘Sure. I’d need exact dimensions on this baby, but I’ve done this before for the bunch over at Crystal City. The hard part’s getting the computer time. I need a big machine.’
‘I can probably arrange access to ours.’
Tyler laughed. ‘Probably not good enough, Jack. This is specialized stuff. I’m talking about a Cray-2, one of the biggies. To do this you have to mathematically simulate the behaviour of millions of little parcels of water, the water flow over – and through, in this case – the whole hull. Same sort of thing NASA has to do with the Space Shuttle. The actual work is easy enough – it’s the scale that’s tough. They’re simple calculations, but you have to make millions of them per second. That means a big Cray, and there’s only a few of them around. NASA has one in Houston, I think. The navy has a few in Norfolk for ASW work – you can forget about those. The air force has one in the Pentagon, I think, and all the rest are in California.’
‘But you could do it?’
‘Sure.’
‘Okay, get to work on it, Skip, and I’ll see if we can get you the computer time. How long?’
‘Depending on how good the stuff at Taylor is, maybe a week. Maybe less.’
‘How much do you want for it?’
‘Aw, come on, Jack!’ Tyler waved him off.
‘Skip, it’s Monday. You get us this data by Friday and there’s twenty thousand dollars in it. You’re worth it, and we want this data. Agreed?’
‘Sold.’ They shook hands. ‘Can I keep the pictures?’
‘I can leave them if you have a secure place to keep them. Nobody gets to see them, Skip. Nobody.’
‘There’s a nice safe in the superintendent’s office.’
‘Fine, but he doesn’t see them.’ The superintendent was a former submariner.
‘He won’t like it,’ Tyler said. ‘But okay.’
‘Have him call Admiral Greer if he objects. This number.’ Ryan handed him a card. ‘You can reach me here if you need me. If I’m not in, ask for the admiral.’
‘Just how important is this?’
‘Important enough. You’re the first guy who’s come up with a sensible explanation for these hatches. That’s why I came here. If you can model this for us, it’ll be damned useful. Skip, one more time: This is highly sensitive. If you let anybody see these, it’s my ass.’
‘Aye aye, Jack. Well, you’ve laid a deadline on me, I better get down to it. See you.’ After shaking hands, Tyler took out a lined pad and started listing the things he had to do. Ryan left the building with his driver. He remembered a Toys-R-Us right up Route 2 from Annapolis, and he wanted to get that doll for Sally.
CIA HEADQUARTERS
Ryan was back at the CIA by eight that evening. It was a quick trip past the security guards to Greer’s office.
‘Well, did you get your Surfing Barbie?’ Greer looked up.
‘Skiing Barbie,’ Ryan corrected. ‘Yes, sir. Come on, didn’t you ever play Santa?’
‘They
