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Equipment Used Afloat, Ashore New Propeller Log Gives Revolutions per Minute for Each Shaft and Average—Also Gives Speed Corresponding to the Average Revolutions E knows his ship, is an expres- sion which is often heard. The essential meaning of _ this phrase applied to the navigator is that under any given conditions he has, through experience with a par- ticular vessel, acquired a sort of sixth sense as to how she will behave un- der varying weather and tide condi- tions for certain engine speeds and position of helm. Having this knowl- ,edge he will without hesitancy signal the engine room for any degree of speed required ahead or astern. In the engine room the signals for vary- ing speeds ahead or astern mean only one thing, and that is, varying the engine revolutions in either direction. The real basis for this knowledge of the ship is therefore the number of revolutions of the propeller. - A really practical and accurate revolution counter would consequently be of in- estimable value to the navigator in asking for, and the engineer in giv- ing, the correct speed. Furthermore the navigator could with the help of such an instrument learn to know his ship with much greater precision. After a ship has been standardized, which is done for navy vessels on their trial trips by making a great number of runs over a measured mile course from the lowest to the high- est speeds, and which may be done for merchant ships as a matter of observation during working condi- tions, a definite relation is established between the number of revolutions of the propellers and the speed of the ship, due allowance being made for tide, weather, loading and condition of the bottom. Sufficient experience with a ship will therefore establish an accurate relation between the _ pro- peller speed and ship speed under any conditions. Hence the primary problem is to determine the propeller revolutions, and where there is more than one pro- peller, the average revolutions accu- rately and in a practical manner so that this figure for each minute is constantly before the eye of the navigator. Secondly, to furnish the navigator with the actual speed of the ship in knots corresponding to the revolutions according to that particu- lar vessel’s ratio of speed to revo- lutions. George Walker, an inventor of Bos- ton, after ‘several years of study and experiment has perfected an instru- ment for determining the revolutions of each propeller, the» average revo- lutions when there are two or ‘more propellers, and the _ corresponding speed of the ship. The writer wit- nessed an entirely successful shop test of this apparatus in Boston. A sea trial is soon to be made and there is every reason to believe that this will be equally successful. The accompanying illustrations and the following description were fur- thus showing continuously for the minute just elapsed the number of revolutions of each propeller and the average number of revolutions of all the propellers. From the average propeller speed per minute, the distance the ship has traveled is computed and the miles traveled is continuously recorded. The mileage counters may be reset to zero at any time while the instrument is in operation. The instrument is de- signed for ships having one, two, saffors fiet eon brow roe RSs. Sherreenetbens sos) 7 A COMPLETE INDICATING UNIT OF THE PROPELLER LOG FOR A TWIN SCREW SHIP— THE TOP ROW POINTERS WILL MOVE FOR ONE MINUTE AND THEN STOP FOR ONE MINUTE DURING WHICH THE LOWER ROW POINTERS MOVE, AND SO ON—THE POINTERS WHICH FOR THE TIME BEING ARE STATIONARY POINT TO THE READING FOR REVOLUTIONS OF THE PRECEDING MINUTE nished exclusively to MARINE REVIEW through the courtesy of Mr. Walker. The instrument is electrically oper- ated and is absolutely automatic in all its functions. When the operating switch is closed, the instrument starts, and automatically adjusts itself, (no matter in what positions the parts may be at the time of starting), and operates continually recording cor- rectly at any and all speeds until the operating switch is opened. It shows, minute by minute, the exact number of revolutions of all the propellers, 369 three, or four propellers. An instru- ment may be used on any ship hav- ing the number of propellers for which it is designed. The distance traveled is computed and recorded by means of two computing cams. The computing cams are designed to cor- respond with the propeller speed curve of the ship on which the instrument is to be used. Furthermore, the instru- ment can be provided with several sets of computing cams corresponding to different sailing conditions of the ship; whether she is heavily laden or