Propeller shaft

“ Two elastic skeins of equal length and strength are attached to a second gear which meshes with the first. The only disadvantage of this form of motor is the long propeller shaft required. The objection, however, is sometimes outweighed by the fact that it is possible to employ a small gear wheel on the shaft meshing with a large one between the bands so that the action of the elastic is multiplied and a greater number of propeller revolutions secured where the length of the bands is limited and could not be increased in order to bring about the same result. ”

“ The engines are supported by two steel tubes held by four brackets bolted to the crank case, these being carried by twelve duralumin tubes bolted to the bearers and transverse frames of the car respectively. The drive from the engine is transmitted through a universal joint to a short longitudinal shaft, running on ball bearings. This shaft gears into two transverse shafts, which drive the propellers through the medium of a gear box to the propeller shafts, making five shafts in all. ”

“ In order that no balancing feats shall be required of the person in charge, there is, on the supporting standard, a quadrant, in the notches of which a lever on the engine frame engages, thus allowing the rigid framework, and therefore the propeller shaft, to be maintained at any angle to the vertical without trouble. ”

“ The bossing out of the stern, as in the Teutonic and Majestic, permits the screws to work without any exterior overhanging bracket, as in other screw steamers. The central boss of the propeller is made of steel; the three blades, weighing eight tons each, are of manganese bronze. A new feature in the machinery is what is called an “emergency governor,” which, in case of the shaft breaking, or the screw racing from any other cause beyond a certain speed, is designed to act automatically on the reversing gear and stop the engines. These gigantic engines are started and reversed by steam. ”

“ They were connected each to a propeller shaft and also to a dynamo used either in lighting or for furnishing power to the wireless installation. One of these engines with its propeller was placed at the [212] back of the large forward gondola; two were in the amidships gondolas, and three were in the after gondola. In the last case one of the propellers was in the centre line of the ship, and the shafts of the two others were stayed out, one on either side. The gasoline-tanks had a capacity of two thousand gallons, and the propeller shafts were carried in ball bearings. ”

“ They can’t stand all this driving and racing, with the propeller blades half out of water every second revolution of the shaft. No engines could stand it, with such a heavy sea on and the ship rolling and pitching all the time like a merry-go-round at Barnet Fair. The governor is no good; and, though Grummet or Links have their grip on the throttle valve all the while to check the steam, and I’ve every stoker and oiler on duty, the bearings are getting that heated that I’m afraid of the shaft breaking at any moment. Full speed, sir? ”

“ They can work up to 4500 horse-power with steam in the boiler at 15 lbs. and revolving at 45 strokes a minute, the expansion valve cutting off at one-third of the stroke; but, with steam at 25 lbs., without expansion, and cutting off at one-fourth of the stroke, they can propel with a power of 6000 horses, so that the combined force of paddle and screw engines gives the tremendous power of 11,000 horses! The propeller shaft, in two parts, is 160 feet in length and [Pg 504] weighs 60 tons, while the screw-propeller itself is 24 feet in diameter with 44 feet pitch. ”

“ The outer bearings of the propeller shafts, always difficult to regulate and keep in order on the twin screw system, are selfadjusting and accommodate themselves to every change of the direction of the shafts. ”

“ They weighed 500 tons. Six double-ended tubular rectangular boilers gave steam at 25 lb. pressure. The propeller was a four-bladed cast-iron screw 36 tons in weight, and of 24 feet diameter and 44 feet pitch. The shaft of the propeller weighed 60 tons and was 150 feet in length. So as not to interfere with her speed when the screw should not be working, two small auxiliary engines were fitted to keep it revolving when disconnected from the main engines. Her speed under the screw alone was about nine knots. ”

“ Before leaving for our camp at Kitty Hawk we tested the chain drive for the propellers in our shop at Dayton, and found it satisfactory. We found, however, that our first propeller shafts, which were constructed of heavy gauge steel tubing, were not strong enough to stand the shocks received from a gasoline motor with light fly wheel, although they would have been able to transmit three or four times the power uniformly applied. We therefore built a new set of shafts of heavier tubing, which we tested and thought to be abundantly strong. ”

“ During the duration of the Liberty program, four crankshafts failed from fatigue, failures starting from sharp corners at bottom of propeller-hub keyway. Two of the shafts that failed showed torsional spirals running more than completely around the shaft. ”

“ The general type of hull is the same as that of the Yarrow and Thornycroft, except that it is of composite construction, having a steel frame with wood planking below water and steel above. The propeller is a single two-bladed screw, placed under the keel just abaft the middle of the boat, the hollow steel screw-shaft being put in on a curve. The rudder is of the balanced type, and is suspended underneath the after-part of the keel. The pilot-house is abaft the smoke-pipe. ”

“ Extending out from the forward end of the tube is a small propeller, the purpose of which is to set the firing mechanism after the torpedo has run a certain distance from the vessel from which it has been fired. This is a safety device to prevent the torpedo from being exploded near its own ship. The torpedo running through the water causes the propeller to revolve, which turns a shaft. After the shaft makes a certain number of revolutions it sets a firing pin, and then if it hits an object it will explode. ”

“ The transmission and propeller shafts were at first made of tubing one-sixteenth of an inch thick, but these were abandoned both on account of the necessity of abandoning the screw-thread method of attaching the flange couplings and gears, and also because these shafts had been designed when it was expected to transmit only twelve horse-power to each propeller, while the increase of power in the large engine necessarily required much stronger shafts. ”

“ A, B, blank from which propeller is shaped; P, P, pencil lines at centre of bend; C, D, sections of blade at points opposite; E, G, propeller after twisting; H, view of propeller endwise, showing outward twist of tips; also shaft.
As the propeller is the most difficult part to make, it is best to begin with it. The flat blank is cut out of the whitewood, and subjected to the action of steam issuing from the spout of an actively boiling tea-kettle. The steam must be hot; mere vapor will not do the work. ”

“ She was capable of carrying 2500 passengers and the crew numbered 860.
The largest plates employed in the hull were 36 feet long, weighing 41⁄2 tons each, and the largest steel beam used was 92 feet long, the weight of this double beam being 4 tons. The rudder, which was operated electrically, weighed 100 tons, the anchors 151⁄2 tons each, the center (turbine) propeller 22 tons, and each of the two “wing” propellers 38 tons each. The after “boss-arms,” from which were [Pg 180] suspended the three propeller shafts, tipped the scales at 731⁄2 tons, and the forward “boss-arms” at 45 tons. ”

“ The weight of the turbine engines of this vessel is only 3 tons, 13 cwts., and the whole weight of the machinery, including boilers and condensers, is only 22 tons, with an indicated H.P. of 1576, and a steam consumption of but 16 lbs. per hour. The weight of the turbine is only one-fifth of that of marine engines of equal power; the space occupied is smaller; the initial cost is less; not so much superintendence is required; the charges of maintenance are diminished; reduced dimensions of propeller and shaft suffice; vibration is eliminated; speed is increased ”

“ The Majestic is propelled by four of these propellers, two on each side astern. Turning at 180 revolutions a minute they utilize 80,000 horse power. One might think that propellers would waste much of this power—that is, that they might turn in the water without pushing the ship forward very much, as a wood screw sometimes turns round and round without getting a grip on the wood into which the carpenter wishes to drive it. This is true to some extent when a ship is first starting, but once the ship is in motion a properly designed propeller will be 95 per cent. ”

“ Turning to the means of propulsion, we find sails as the main, or almost only, reliance during the early years of the century. The steam-engine operating paddle-wheels had come to be recognized as a possibility, and under certain conditions as a commercial success. The screw-propeller as a means of propulsion was known only as a freak idea, and was without status or recognition as a commercial or practical means for propelling ships. ”

“ He further contended that the proportion of stroke to diameter should be greater in an engine that is to drive a screw propeller direct than what is required for applying the same power to a paddle-wheel, and it would soon be found that as an instrument of propulsion, even for great speed, the screw would not be inferior to the most approved patent paddle-wheel. ”

“ Of course, it will be understood that we are not taking into account resistances, and defects proper to the screw, from which hydraulic propulsion is free, nor are we considering certain drawbacks to the efficiency of the hydraulic propeller, from which the screw is exempt; all that we are dealing with is the waste of power in the shape of work done in moving water astern which we do not want to move, but cannot help moving. ”

“ While the last few years have seen great advances made in the designs of steamships and of their engines, little or nothing has been done in the way of improving the screw propeller. As a general rule it would appear to be taken for granted that no radical improvement could be made in the form of the propeller, although various metals have been introduced in its manufacture with the view of increasing its efficiency. For sea-going steamers, however, the shape remains the same, the variation chiefly relating to the number of blades employed. ”

“ The elongated hull and ballonet were resumed, and the stiffening pole was elaborated into a longish car resembling Renard’s, but of triangular cross section. On this long trussed frame were placed the motor, propeller, rudder and the rider in his basket. A seven horse-power engine turning, at one hundred revolutions per minute, a screw propeller having two blades, each 13 feet across, gave a thrust of 66 pounds. ”