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16 MARINE REVIEW. [July 5, IMPROVEMENTS IN SCREW PROPULSION. By I. MCKIM CHASE. When advocating improvements in screw propulsion in a direction which has been little explored, doubt has sometimes been expressed as to the possibility of utilizing water that has once been acted on iby a screw propeller to further aid in producing thrust. It is urged that after being once acted on the usefulness of the water for producing thrust is ex- hausted so far as the vessel to which the screw is applied is concerned. Such opinions result from a failure to fully comprehend the principles in- volved in marine propulsion. At the risk of being thought prolix I will endeavor to make the principles of marine propulsion plain to any ordi- nary person and elucidate at least one way by which the water discharged by a primary propeller can be further made to produce thrust. A gun is such a familiar instrument and its behavior when fired so widely understood that it will make a good medium by which this may be done. Fig. 1 represents a gun secured to a-float. Should the gun be fired the recoil resulting : from the discharge of the Leg. e projectile and powder will tend to move the float in a direction opposite to that 7-- =~ of the discharge. This 5 Z movement will be increased See SSS as the weight of the projec- tile and powder increases or diminishes as that of the gun and float is diminished. It will be observed in this case that there is present a= condition which obtains in every case of marine pro- pulsion, namely, that it was necessary first to perform certain work, and that it was the reaction of the pressure required to per- form this work that pro- duced the thrust to move the float. It should tbe fur- ther noted that the work done by the explosion of the powder charge is divi- ded between that required to move the projectile in one direction and the gun and float in the opposite direction. Evidently the energy present in the mov- ing projectile was absorbed from that evolved 'by the explosion of the.powder, and while so present it could not be engaged in moving the float. The amount of energy absorbed in the movement of the projectile represents the wasted but necessary preliminary work that is required for the production of thrust in marine propulsion. Econom- ical considerations, however, demand that as little energy as possible be wasted in this preliminary work, and the chief purpose of this argument is to demonstrate how it is possible for this to be accomplished. The operation of an ordinary water wheel of the turbine type is readily understood because the different features of its operation are nearly all visible. The movement of the water by virtue of its gravita- tion and the impulse it gives to the wheel to cause its rotation are easily comprehended. When the water passes away from a turbine after per- forming work it possesses less motion than when it entered the wheel, the amount depending on the work performed during its action upon the wheel. In the case of screw propulsion the operation is the reverse of that of the turbine. The ultimate object sought is the driving of the ship, and in order to accomplish this it is necessary to produce an end pres- sure or thrust on the shaft. The screw is made to discharge a quantity of water, and the reaction of this produces the thrust. In this case, eliminat- ing the following wake which prevails with all advancing vessels to a greater or less extent, the water is at rest. The screw being made to rotate by the engine causes a movement of the water which is in contact with it, and this movement is accelerated while the water is being acted on until it is discharged by the screw. In many instances the water so discharged has considerable velocity. It is evident that such water is just as capable of perfonming useful work as that which is given motion by gravitation. When a screw propeller is driving a ship the power ab- sorbed in doing so is divided 'between that required to move the ship and that to move the quantity of water in the opposite direction neces- sary to produce the thrust. Another factor which enters largely into the problem of screw pro- pulsion is the inertia of the water acted on or the resistance it opposes _to 'being put in motion 'by the screw. But the chief factor is the reac- tionary effect of the water discharged by the screw, and it is the main purpose of this argument to demonstrate how this discharged water, which has once served its purpose, may be further utilized to aid in pro- pelling the ship. The same principle obtains with all systems of marine propulsion, whether it be by paddle, screw, or jet. The latter is here selected as presenting the simplest form for illustrating the method by which the discharged water from the propelling instrument may be em- ployed to assist propulsion. _ . Fig. 2 represents a boat provided with a nozzle. Ifa stream of water is discharged from the nozzle the reaction resulting therefrom will move the boat in an opposite direction to that of the discharge. It makes but little difference in the reactionary effect whether the discharge occurs below or above the surface of the water. The reactionary effect occurs while the fluid is moving in the pipe and ceases entirely after the water has moved from the nozzle a distance equal to about one-fourth of the diameter of the orifice. While the water discharged will cease to have any reactionary effect as above stated, it will continue to move and it is possible for it to have considerable energy impressed upon it. In the hydraulic system of mining as practiced in California streams of water are made to issue from nozzles with tremendous velocity. In some instances a stream will carry an enormous amount of energy, and be so dense and rigid that a reliable authority has stated that an ax could not be driven through it. gu face of the country in some districts has n entirely changed 'by these streams. : : ' cS Fig. 3 sae die ie boat, modified by having added to it a pair of paddle wheels with an impact or Pelton wheel geared to the paddle. shaft, Thus arranged the cups of the wheel receive the impact of. the stream of water after it ceases to have any reactionary effect on the noz- zle. The action of the stream will cause the rotation of the paddle- wheels with the result that the propulsion of the boat will thereby be in- creased over that it receives from the jet alone. The Pelton wheel in combination with the jet serves the purpose that guide blades would if connected with a screw propeller. The method. which promises the greatest success in utilizing the discharged water from a screw propeller to aid propulsion is by the use of guide blades in combination with the screw. The conditions which generally surround the application of screw propellers makes the combination of guide blades with the screw somewhat more difficult than the above arrange- ment with the jet, but success has been achieved with problems much more difficult. CANADA'S CANALS. THE BRITISH VICE-CONSUL AT OHIOAGO PREPARES A REPORT ON THE POSSIBILI- TIES OF DIRECT TRADE BETWEEN THE LAKES AND LIVERPOOL. Reports on commercial subjects from our own consuls in distant countries are sometimes hurriedly prepared and not always reliable as to detail. The same may be said of a report prepared by Thomas Erskine, British vice-consul at Chicago, on the subject of direct trade between lake cities and England as a result of the opening of Canada's St. Lawrence canals. Of course Mr. Erskine lays particular stress on the chances of trade for British ships from Chicago (flour, grain, provisions, etc.), but he also refers to all the large ports on the lakes. The practical vessel owner of the lakes sees much to criticize in all the discussion relative to direct trade (between the lakes and Liverpool, but Mr. Erskine's report, taken for what it is worth, will nevertheless prove interesting. Opening with the total amount of shipments and arrivals at Chicago last year, the report goes on to show the advantages of the Canadian artificial route to salt water. It says: "Tast year (1899) Chicago shipped by rail and lake 221,972,000 bushels of grain, and 5,421,000 barrels of flour, and of this only about 12 per cent. was shipped to Canadian ports, but with the opening of the Welland canal, giving a direct passage to the Atlantic for vessels of about 1,500 tons register, it is expected that an increased quantity of grain will be shipped to Montreal, and there loaded on larger vessels. It is also thought pos- stble that vessels may find it profitable to bring merchandise direct to the lake ports and return to Liverpool loaded with grain and flour." Continuing, the report expands on Canada's ability to offer rates competing with the Erie canal to New York and the agitation now being carried on in New York state for the expenditure of $60,000,000 to im- prove the American waterway. It is asserted that New York stands to lose much trade unless the Erie canal is made navigable for large lake barges to run direct to New York, and there trans-ship their freight to ocean-going ships. '"The Canadian canals," says the report, "may bring some British vessels into the lakes, and, if successful, may lead to a big trade, and a consideration of the conditions of the class of vessels able to --pass through the St. Lawrence river and canals will interest ship owners and others engaged in marine work. "Canada has connected Georgian bay with Montreal by rail, and the Canadians now advocate making a canal from Georgian bay to the Ot- tawa river, giving a direct waterway which, while shortening the distance from Chicago and Duluth to Montreal by about 400 miles, would save the expenses of the Welland and other canals and the difficulties of the upper St. Lawrence. The only drawback to the Welland canal, which it is hoped will not be found in the Georgian bay canal, if it is constructed, is that it was not planned on a broader scale as to dimensions, as the modern freighter can deliver to the railroads and Erie canal three times as much grain as can be carried' by a vessel of the St. Lawrence and canal tonnage. _. The trade opened by the Canadian canals, to which the attention of British ship owners is called, is for vessels which will pass through the canal locks, which are of the following dimensions: Length, 270 feet; width, 45 feet, and 14 feet depth, and which will trade either direct with ports in the United Kingdom or carry their freight to Montreal and there transfer it to ocean steamers, and the extent of this trade will depend upon whether, with economy in coal, etc., British vessels can compete with the large freighters which carry the grain for the railroads to New York. That British shipping does not have its proper share of this trade is shown by the fact that while there were 161 vessels entered at Chicago and South Chicago in 1899 from Canada, only twelve of these were British, the rest being American. The distance from New York to Liver- pool is 3,053 miles, while from Quebec it is only 2,600 miles, and the dis- tance from Quebec. to Chicago, the furthest port on the lakes, is 1,400 miles, The direct imports to Chicago in 1899 were valued at 2,824,282 pounds, and of this amount Great Britain is credited with 653,546 pounds. nearly all of which must have come 'by Atlantic ports of the United States, and then by rail, or from American ports on the lakes, and, of course, does not take into account importations cleared at the New York custom house and then sent on to Chicago." The pith of the matter is said by Mr. Erskine to lie with the British vessels drawing 14 feet of water in the canals being able to compete with the large American freighters and the railways by 'bringing merchandise from the United Kingdom direct to Chicago and other lake ports, and returning with grain. The following are stated as the conditions under which the ocean ships would travel during the lake end of their trips: A vessel could carry enough cargo to Montreal to enable her to pass through the canals and there load down to her seagoing water line, and in this way vessels of greater draught but of the proper length and breadth could be used in the trade; it would be necessary to have a pilot on board from Quebec whose remuneration would not exceed $5 per day; the ques- tion of extra insurance rates on account of the more northerly latitude at which the vessels would cross the Atlantic and because of their being navigated on an inland sea would also require adjustment, although the