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July, 1925 _ TUG BOAT RUSSEL NO. 2—NEWTON CREEK TOWING CO.—FITTED WITH 135- HORSEPOWER LOMBARD DIESEL ENGINE —EQUIPPED WITH 5 INCHES SIZE MAXIM SILENCER INSTALLED IN STACK by the Maxim Silencer Co., Hartford, Conn. The theory of operation, the construction and the use of silencers under ordinary conditions of gas flow are interestingly described in a new catalog brought out by this company. Two questions would naturally arise in regard to any silencer, the first, what the effect will be on back pres- sure and the second how much of the noise in extracted. Considering the two cycle engine, in which obviously the effect of back pressure would be more serious than in the case of a four cycle engine, increasing the back pressure of the outlet of the exhaust gases at the beginning of their move- ment is permissable if a correspond- ing decrease in resistance is obtained at the end. The manufacturer claims that this is exactly what happens as the pas- sages of the silencer are long and free. An exhaust pulsation entering the silencing unit is slightly impeded at the start but when the long column ot gas in the silencer passages is started in motion it tends to persist in motion, and actually serves as a partial vacuum towards the end of the exhaust period. If the exhaust port of the engine closes just at the moment of lowest pressure, the best engine performance is obtained. In regard to the proportion of noise extracted we are told that this is a matter of compromise. Ninety per cent reduction is readily obtainable; the next 5 per cent requires a big in- crease in the silencing parts; the next 3 per cent a still greater increase in proportion. Complete 100 per cent extraction is not feasible. The silencers are therefore proportioned to meet practical needs and kept within rea- sonable dimensions and price. The gas pulse first passes into a MARINE REVIEW TANKER TEXACO 125--TEXAS OIL CO—LENGTH 96 FEET 5 INCHES—BEAM 23 9 INCHES—DRAFT 10 FEET 3 INCHES—FITTED WITH 200 BRAKE HORSEPOWER 271 concentric annular channels. These channels communicate with each other in stages by longitudinal ports in the cylinder sides. Silencers built on this principle are particularly effective in quieting sharp hissing noises and are used on air compressor blower intakes and on four cycle diesel exhausts. The diesel engined tug and small tanker illustrated herewith are both equipped with silencers. That the silencer serves a very practical pur- FEET i FAIRBANKS MORSE & CO. TYPE C-O ENGINE—EQUIPPED WITH 8 INCHES SIZE MAXIM SILENCER ON EXHAUST comparatively small expansion cham- ber which smooths delivery in the same way as an air chamber on a re- ciprocating pump, and further pro- vides a place where solid and liquid matter in the gases can deposit for easy removal.. The silencing unit proper, into which the gases then pass, trap out the noise wave in one of two ways: First, by utilizing repeated reflec- tion to dissipate the energy of the wave. Second, by stretching out or sub- dividing the wave over a longer time interval so that it reaches the ear in small dulled fragments. Distinctly different silencing unit construction is required for the two principles, and that chosen depends upon the noise conditions. Units built on one or the other of these two lines have been found to meet all noise problems. Silencing by repeated reflection is accomplished by building the unit of cast sections which when assembled form parallel spiral passageways. This principle is used most frequently for two cycle exhausts. Silencing by subdivisions is obtained by building up the unit of cylindrical plate of different diameters set be- tween flat heads to form a series of pose, and if properly designed and in- stalled, that it does not rob the en- gine of any power, is quite clearly demonstrated by the increasing num- ber of craft making use of it. Engine Speed Indicator for Marine Use Every commander whether he be on board of a battle cruiser, a yacht or an old tramp is entitled at all times to receive accurate information auto- matically conveyed to the _ bridge. on the position of the helm and what revolutions the engines are turning up. Many accidents can be traced to lack of or inaccurate information received on these important points. To complete its line of aids to navi- gation and particularly as a compan- ion instrument to its helm angle indi- cator, the Sperry Gyroscope. Co., Brooklyn, N. Y., has brought out a new type of engine speed indicator, the component parts of which and method of installation are shown in the accompanying illustrations. This engine indicator will show at any desired position on the ship, the num- ber of revolutions per minute of the main engines or the propeller shaft and whether or not these revolutions are ahead or astern. But in addition