A few weeks ago the editor of the Proceedings took advantage of an opportunity to go aboard the new Italian liner Conte di Savoia. He was much impressed with the equipment, decorations, and appointments of the public rooms; particularly the beautiful “Colonna Hall” with its tapestries, statues, murals, and general air of taste and luxury. But while the passenger accommodations were, to him, of more or less academic interest, he found the emergency equipment and the navigating equipment of more technical importance. The size, strength, and efficiency of boats and launching gear, and the motor lifeboats were illustrative of the great progress made in insuring the safety of life at sea since the days of the Titanic. The efficiency, completeness, and ruggedness of the navigation and ship-control equipment was a joy to behold. He left the ship feeling that the Italians had built a vessel in which they might justly take much pride.
The writer found much to hold his attention, but nothing left him with more food for thought than did the gyro-stabilizer. In a compartment far down in the forward part of the vessel are three 13- foot flywheels each weighing 110 tons that may operate separately but simultaneously at 800 r.p.m. These flywheels with all their appurtenances, appliances, accessories, foundations, and associated structure weigh 750 tons and may absorb as much as 2,000 hp., but they can and have kept this 48,000-ton ship on virtually an even keel in rough weather. This equipment, costing about $1,000,000, was built by Vickers; but an American concern, Sperry Gyroscope Company, holds the patents, designed the plant, and superintended its construction, installation, and operation. In keeping with so many other mechanical and electrical developments of the past twenty years, the matter of ship stabilization has progressed by leaps and bounds. The earlier installations on the Worden, the Henderson, and the G-4 (or was it some other submarine?) now appear as antiquated and inefficient as the aero engines and planes that were in use about the same period.
We found it difficult to credit Captain Antonio Lena’s statement that by cutting in the stabilizers the ship’s roll of thirty degrees (complete arc) was reduced to less than three degrees on a side, but the automatic recorders bore him out. An examination of other automatic records showed that as the rolling was reduced the yawing decreased. In fact, it was easily possible to examine the course recorder charts (gyropilot is used for steering) and point out exactly when the stabilizer was operating. An engineer officer gave us another side light. He said that there were not enough data to give exact figures, but that in rough weather, use of the stabilizers, with their consumption of many kilowatts, actually reduced fuel consumption. He ascribed this to reduced losses from yawing, rolling, and inequality of immersion depths of opposite propellers.
We were astonished to find that the foundation of the stabilizers was little if any heavier than that necessary to carry the weight. Additional stiffening was reported as unnecessary because no great strains are carried to the ship’s structure.
It was about then that we began to realize how little we knew of waves, rolls, and stabilization and resolved to make some inquiry on the subject. We learned, of course, that it really takes but little power to counteract any single wave, and that roll results from the many successive waves passing under a ship, each one adding a little to the tilt. The stabilizer is built with the idea that it need be just large enough to meet the turning force of the single waves. If that is constantly done the roll can never build up.
It is not waves impinging against the side that cause a ship to roll but the displacement of the center of buoyancy. The accompanying illustrations, which the Sperry Company has kindly permitted us to use, may help you to visualize what happens. If not, perhaps Ellsberg’s description in the March issue of Fortune will do the trick.
The tired business man, the ship, and the ball share a phenomenon: they roll. Simple the situation, embarrassing the compromise in this triangle drama wherein the three principals are M (the metacenter), G (the center of gravity), and motion.
M is that imaginary point about which a body swerves or rolls. In the ball it is the exact center, and if G coincides with it the ball will roll freely in any direction. But if, as by the introduction of a weight (W), G is drawn away from M, the ball will invariably come to rest with M directly above G. In a ship, M is the center of that circle of which the shifting center of buoyancy (below the water line) describes the arc B-B'. The distance between G and M is the metacentric height, the GM. Obviously the greater the GM the more stable the ball and the more rapidly it will right itself.
So likewise, with his G well below his M, the man to the left takes his fearless ease. If instead he trusted the dotted rockers, with G above M' (the lowered metacenter), he would court overthrow.
And so with the ship and the Navy’s dilemma, about which volumes have been written. If the GM is great and the ship thereby stable, she rights herself with such violent abruptness that accurate gunfire is impossible. If the GM is little, she becomes an equable platform for guns—yet may, in a brutal storm, or from gunfire injuries, capsize.
Looking over old copies of the Proceedings and through the Institute’s library we found but little about waves, rolling of ships, or stabilization. Possibly the Navy as a whole has been as little interested, and probably as poorly informed on this subject as the editor of this publication. Now that our interest has been aroused we should like to know more of “Why They Roll.” Captain McEntee in 1920 read a paper in regard to the relative merits of bilge keels and gyro-stabilizers and the encyclopaedia and some textbooks touch lightly on the question.
Why for instance, after spending considerable money in experimentation, did the American Navy drop the idea of gyro- stabilization about the time it became successful? One reads advertisements of Frahm’s anti-rolling tanks on German liners; but what of the cost, flexibility of control, etc.? Such tanks were in use to a greater or less degree before the World War; has some recent development been made that increases their effectiveness?
Many of us knew that a lot of yachts had gyro-stabilizers installed. But naval vessels aren’t yachts; and, in theory at least, men-of-wars men scorn the idea of getting seasick. But we should like to know if the Italian destroyer Pigafetta with her stabilizer has better gun control and torpedo control than do her sister-ships? And if she is a flotilla leader, will the stabilizer materially aid her in getting the course and speed of the enemy?
Speculate as to whether or not stabilizers would have helped Cradock at Coronel, but ponder too over the fact that the Japanese aircraft carrier Hosho had a gyro-stabilizer installed many years ago and that the new carrier Ryujo, completed last year, has a similar installation.
Do carriers with stabilizers enjoy an increased freedom of action in sending off or in recovering planes? Stabilizers check normal rolls, but how much aid are they to a destroyer making 30 knots in line of bearing where it is catching the bow wave of the next ahead? And finally will stabilizers permit a commander in chief to deploy on a more favorable course than would otherwise be possible?
Probably few of those who read these pages will ever become any more intimately acquainted with the workings of the gyro-stabilizer than they now are with the gyrocompass. But most of them might wish to know if this is a development of which the Navy should take cognizance. Possibly some officer has already inquired fully into the merits and demerits of such equipment, and will give the results of his investigations to those who know so little.