New Britain herald., 1917-12-10
FACIS ABOUT THE AMERICAN NAVY
Screw Propeller
BY LIEUT. FITzHuGH GREEN. D. g. N

Next to being a sailorman I think I'd rather be an anthropologist than anything else in the world. I could then find out all the interesting hows and whens in regard to our customs and crafts, and especially how we came into them. For instance: Prlnciple of the Screw means next to nothing to the average man. Screws hold down hinges, panels and thermos bottle covers. Screws are the little metal gadgets which are always getting lost A nut Is an inside screw And so on, until the sum total of popular knowledge about screws amounts to the fact that they go in or out according to the way you twist them.
 As for ships propellers, most of us don't even connect them with screws at all. Yet the theory of them considers water as solid as wood and the prOpeller's advance analogous to that of screw revolving through substantial and uryielding medium. Truly enough a vessel bores ahead
 Way back in the Stone Age men knew screws. Recently discovered tribes of Eskimos give us good sam ples of primitive mans invention and use of spiral grooves on hunting inn plements. Threaded bone plugs are still used to stop wounds in sea game lest the body sink. Seals especially are inflated by the hunters blowing into the harpoon cut and screwing in little rough-hewn peg.
 It is curious that very nearly the first use of screw propellers on ves- sels came with the development of submarines. In 1795 David Bushnell ,l.l< l. f1oated upright. He had two sets of revolving oars as he called them. that were really screws. He was afraid someone would bag his idea before he perfected 1t.
 These oars were real screws. That is, their blades comprised a spiral sur face through one complete turn. That one in a horizontal plane raised or lowered the craft; while a common vertical screw propelled her.
 John Stevens in 1894, without any definite knowledge of the egg Bush nell was so secretly trying to hatch, fitted a screw on his IS foot steam boat. Very early in the game he req lized that only a small percentage of the screw area could be utilized. Ra- pid revolution threw the water away and left nothing to push against. So came aDOut our present DlaOeO pro- pel1er. which is merely three or four sections of the helix. and carried through only a fraction of g. turn.
 This having something to push against" is the great problem in propeller design. Some years ago an interesting tank experiment was car ried out to investigate unexplained speed losses. Of course if water were solid the faster the screw revolved the faster the ship would travel. But water sweeps away very easily. This was shown by throwing a beam of light directly on the blades at one point in the circle. After a certain speed was reached what looked like a lareO h&iDtOr developed about tAO middle oR xAe b1Rde area. In reality this was . :ppot of vacuum. :, WateT was being shot out radially by the propeller faster than it could flow back.
 So that now on our fast cruisers and destroyers we carve away the after hull and give body lines that induce a flat flow into the screw. High speed turbines must be geared down to suit the sluggish water, and propeller:' themselves made only steep enough to give push without outrunnlng tnelr push medium"
 And thought 1t hasn't any real bear" ing on the subject, can't you see no"