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Pressure 9 Workin uad Engs. X uperheat S$ FIG. 1—RESULTS NOTED IN TABLE II PLOTTED TO SHOW GRAPHICALLY, PER- FORMANCE OF LAKE VESSELS WITH VARIATIONS IN POWER PLANTS (Continued from Page 58) It will be observed from this time the contenders for the place of honor, the lower left-hand corner, are exclusively triple engines with scotch boilers and saturated steam. It may also be added that without exception they are equipped with jet condensers and attached auxiliaries. The closer the approach to the corner the lower both capital and operating costs become. If any lesson could be drawn from this it would seem to be that the most suitable working pressure for all-round purposes is about 170 pounds per square inch. This agrees entirely with the writer’s own experience from which some interesting figures could be supplied but for the limitations already laid down, but it may at least be said that their effect would be to lower the average of column 3, Table II. Cost Of Operation Is Affected If we sit down with this information before us and attempt to estimate the economic features for a given ship of modern type of say 2200 indicated horsepower it works out something like this: using the indicated horse- power as a basis we can of course only consider the running time, or hours under way, and which for the average able ship in the average trade may be approximated at 150 hours per trip, but since a part of this time is at reduced power, suppose we say 140 hours at normal duty and 10 hours at about 1/3 power or 800 indicated horsepower, which gives a total of 316,000 horsepower hours. If the apparent difference in fuel efficiency actually existed the difference in fuel per trip in favor of scotch boilers would be about 57 tons (of 2000 pounds) or at average prices for the past season about $300 per trip, or, at 30 trips for the season, about $9000 for running time only. As with all calculations based on av- erages this figure is only approximate and may ,be in error for a specific case but the error may be in either direction. It may seem too high but it is equally possible that it is too low. Of course variables’ will occur as’ to hours under way, etc., but in general these do not affect the reasoning, they only affect the actual result. February, 1927 On the other hand there is a claimed saving in weight. Reliable figures are fortunately at hand applicable exactly to the case. Three pair of ships with exactly similar hulls and engines are available for comparison and represent the latest additions to a fleet in which all belong. Column 1 gives figures for scotch boilers and 2 and 8 for water-tube boilers. It will be understood that each column applies to a pair although the fig- ures are for one ship. Engines in all cases are of standard triple type. Mechanical heated draft is fitted in ship 1 and mechanical unheated in 2 and 3. (See Table III below). It will be observed that considerable uncertainty apparently attended the installations in 2 and 3. Ship 2 shows for the same power nearly 16 per cent more heating surface and 44 per cent more grate surface than ship 1. For ship 3 the heat- ing surface is again increased to 37 per cent over ship 1 and the grate surface is reduced so that it is 16 per cent above ship 1. The ratio of heating surface to grate area thus stands at, 42, 34 and 50 respectively. In other words the relative pro- portions as between 2 and 3 have apparently undergone an _ alteration of a’most 50 per cent. Ship 1 is a type of which a number have been built without modification. Difference In Weight Presumably ship 3, which appears to represent latest practice, may be taken for the purpose of weight comparison with ship 1. It will be seen that the difference in boiler weights, including the water in the boilers, is about 60 tons, lying al- most entirely in the water content and in the air heaters. These items are the most valuable things in the entire ship, the former constituting what Professor Rateau has so aptly described as “a steam fiywheel” and TABLE III Comparative Weights and Costs of Scotch and Water Tube Boilers Nimmber: of DOMETS Viiieinitstienan Total heating surface, square feet Total grate area, square feet ........... Superheat Weight, water in boilers, pounds Weight, furnace fittings, pounds CBAATEwWONe Weight, f 10 Weight, 11 Weight, 12 Weight, 13 Weight, 14. Weight, an and engine, pounds boiler mountings, air heaters, stack,” DOUNGS *-Avicsiscsccssess boiler covering, pounds flue blowers, pounds pounds 15 Weight, total pounds 16 Cost, approximate Weight, boilers and superheaters, pounds Soe neneee Weight breechings and uptakes, pounds pounds ..... Ween eee eee geneeeseeeererenes 2 3 1 Water- Water- Scotch tube tube 3 3 3 5,814 6,695 7,965 137.5 197 159 yes yes yes Sieh liecaache 250,900 249,500 268,500 Rae eRe rhe hee 135,000 40,000 48,000 Rog bRcmeaoeucs Veet Rar aTeee 30,800 13,400 18,400 sop staudncgudgudeaseeeasccd 14,300 18,700 20,000 SE Tee pasa coche obumucenvanzs 6,500 7,500 7,500 Sachieveleces recur cannot: 9,000 3,500 7,500 none none 13,560 15,000 2,000 2,100 eel Ga Neduveud cao Waavendcatinng: none none Reva Saleiceccavaoaartucenaes 509,900 348,160 878,000 edslbvacs aius olen Neanieeesé $60,830 $69,000 $50,260