Returning forward, they passed into the long compartment at that moment presided over by the diligent Clancy. The two great engines occupied every bit of space there save for a central passage barely wide enough to move through. Clancy held forth at length and with enthusiasm on those engines, but Nelson, whose bent of mind was not mechanical, found it difficult to understand what was told him. He did get away with one or two interesting facts, however: as, for instance that the Diesels burned crude oil instead of kerosene or gasoline, at a vast saving, and that instead of having the charges in the cylinders ignited by electric sparks, in the only way he had ever heard of, the engines produced their own heat for ignition by compression.
“It’s like this,” elaborated Clancy. “These are four cycle engines, do you see? That is, one of the pistons does four strokes to one explosion of the charge, two up and two down. Now take this fellow. When the piston in this cylinder goes down it draws a lot of air into the cylinder after it. When it goes up again it compresses that air something fierce; about five hundred pounds to the square inch. That heats the air, do you see, to something like a thousand degrees. Next oil is sprayed into the cylinder by compressed air, and when it hits that hot air already there it lights. That’s what they call combustion, and that sends the piston down again and turns the shaft over. That’s the third stroke. The fourth is the next up-stroke and that pushes the burnt gases out, and there you are!”
Nelson shook his head. “It sounds all right,” he said, “but what makes the engine start first of all?”
“The storage batteries.”
“And how fast will they drive the boat?”
“Sixteen knots at a pinch, but we usually do twelve on account of using too much fuel at high speed. You got to think of fuel, you know.”
“I suppose so. And where do you keep that?”
“Everywhere.” Clancy waved a big hand vaguely. “There’s tanks of it all over. The main tanks are fore and aft, next to the keel, but we’ve smaller ones here and there. There isn’t any space wasted on one of these contraptions, Nep.”
“Why did he call you Nep?” asked Martin curiously as they went on. Nelson explained and his friend chuckled. “That’s not so bad, either. Guess I’ll have to call you that, too. This we call the after quarters, but technically it’s the after battery compartment. About half the storage batteries are underfoot here. You can see the cables leading forward there. These gratings lift up when you want to get at the cells. That’s my bunk there. Those cupboards are where we stow our gear. Next is the central station. Can’t show you around there, though, for the Old Man doesn’t like us hanging about. Everything’s controlled from there, you see.”