Water in tanks (computed by Atlantic Works).. Total weight.... Pounds. 13,000 2,000 31,300 240,753 This weight is exclusive of wood-work and outfits. The total weight, as estimated by displacement, is 113 tons of 2,240 pounds. MANNER OF MAKING THE TRIAL. For the purpose of determining the economic evaporation of the boiler, all coal was carefully weighed, in bags containing 100 pounds of coal each, on a Fairbanks platform-scale. The bags were tallied as they were taken from the coal-shed, a checktally kept on the yacht, and the empty bags afterwards counted to verify these tallies. All water fed to the boiler was drawn by the feed-pump from two, leveled, wooden tanks through a hose, the connection between the pump and hot-well having been broken. These tanks were so arranged that one could be pumped down to the limit, (a block about 2 inches high secured to the bottom of each tank,) while the other was filling. A careful man was stationed at the tank stop-valves, with special instructions to close tight the valve on the tank which had been drawn from, before opening the one on the full tank. Owing to the scarcity of fresh water, the water from the hot-well was pumped into the measuring tanks through a hose, only enough fresh water being drawn from the tanks of the Fish Commission to completely fill one measuring tank before the other was emptied. There were no leaks in the tanks, pipes, valves, and connections to boilers. The tanks were slightly irregular and, therefore, their capacities were determined by weighing them on an accurate platform-scale. The weight of water contained in No. 1 tank at 66 degrees was 1,901 pounds and in No. 2, 1,929 pounds at 70 degrees. A high-grade thermometer was placed in the stop-valve chamber on the steam-drum and another, in throttle-valve chamber at the engine. Thermometers were also placed in the fire-room, on deck in the shade, and in the measuring tanks. It had been the intention to place a pyrometer in the uptake at the base of smoke-pipe, but the instrument did not arrive in time. The approximate temperature of the products of combustion at that place was found by placing small pieces of tin, lead, and zinc on bits of fire-brick supported on the upper rows of tubes at the middle and front of boiler. The reading of the barometer was also taken. At the end of every four hours during the trial, the ash-pans were hauled and the dry ashes weighed. All preparations having been made, fires were started in the usual manner at 12.30 p.m. on Saturday, November 26, 1887, the ship being secured to wharf at the Fish Commission station at Wood's Holl, Mass. Steam formed at 12.50. The engines were then started and kept running until it was found that everything was in working order. At 2 p.m., the fires being in average condition, the water-level was marked on the glass gauge, the feed-pump started on a full tank, No. 2, the coal account begun, and the trial considered as having commenced, all data thereafter being observed and entered hourly in the log. The trial continued twenty-four hours, frequent calorimetric tests being made. The calorimeter and connections were arranged as follows: A clean alcohol barrel, of about 50 gallons capacity, was placed on a very sensitive and previously adjusted new Fairbanks scale, a drain-valve fitted to the bottom, and a thermometer, made by Huddleston, Boston, and graduated to one-half of a degree Fahrenheit, secured in the top head. A hose brought the coldest fresh water in the vicinity from one of the Fish Commission tanks to the barrel. Steam was taken from the center of the main steam pipe, just in front of the throttle, and led to the barrel by a three-fourths inch iron pipe, well covered and about 20 feet long, to which was coupled a short piece of steam hose. A brass diaphragm with a one-eighth inch hole was placed in the coupling to wire-draw the steam. The hose was punctured with several one-fourth inch holes near its free end, to reduce the shocks when steam was flowing into the water in the barrel. The tests were made as follows: The barrel having been drained and its weight with attachments noted, was filled to within 5 or 6 inches of the top, the weight again taken, and the temperature of the contained water noted. Steam was then blown through the pipe and hose until they were cleared of all condensed steam and thoroughly heated, when the hose was put in the barrel and the steam-pressure at throttle noted. When the temperature of the water in the barrel had been raised to about 1110, the water during this time being continually agitated, the hose was quickly removed, and the temperature of the water, weight of barrel and contents, and steam-pressure at throttle noted. From the data thus obtained the quality of the steam (that of "saturated” steam being unity) was computed by the following formula: Where W w (&'—)—(T—t)] = weight of cold water in barrel. w= weight of water added by passing steam into water. T= total heat in water due to the temperature of steam at the observed h' total heat of water of final temperature in barrel. h = total heat of water of initial temperature in barrel. The percentage of moisture in the steam is, therefore, 100 (1 — Q). The observed data and computed results of the trial are given in the following tables, the second one giving the data of calorimeter tests. The evaporation given in the first table is the apparent vaporization from the tank measurements and should be corrected for the percentage of moisture, as found by the calorimeter measurements, by adding to it. From Table II it is seen that the average amount of moisture in the steam is 6.31 per cent. As shown by the above tables, the evaporative capacity of the boiler is not particularly high, and the steam furnished as dry as is usually found in practice where no special provision has been made for drying or superheating. The rate of combustion was only 12.8 pounds per square foot of grate, and it is not certain that, with a high rate of combustion with forced draft, the steam would be as dry. The coal used was Cumberland, of good quality, mined during the present season at George's Creek mine, and was the average run, not selected. The percentage of ash was less than 8 per cent., although a small amount of fine coal fell through the bars and was weighed with and counted as ashes. The fires were not forced, even by the steam-jet over the fire doors, and the smoke-pipe was not sufficiently high to produce a strong draft. The temperature in the uptake was found to be as high as the melting point of zinc, (the sharp edges of which had been slightly touched,) the tin having completely disappeared and the lead melted down and partially oxidized. STRENGTH AND SAFETY OF THE BOILER. In all tubulous boilers, of which the Belleville is one type, dependence is placed upon the rapid production and use of the steam. Their interior capacity is small, and hence, in case of explosion, the quantity of explosive being smaller, the result must be less disastrous than it would be in the case of shell boilers. The tubes and connections of this boiler are of such small dimensions and excessive strength, compared with the strains imposed on them, that the boiler may be termed non-explosive, as far as these parts are concerned. In the Shearwater's boiler, the part subjected to the greatest strain in proportion to its strength is the steam-drum, the strength of which may be taken, there:ore, as the measure of the strength of the boiler. The reported United States Government test of a piece taken from this drum showed a tensile strength of 54,000 pounds per square inch, with a reduction of area of 12 per cent. The thickness of the drum is given as one-half inch, (its actual thickness is 15 millimeters, nearly five-eighths inch,) and its outside diameter is 19 inches. 2ts Taking the usual formula, P allowing 70 per cent. for the strength of double-riveted seams, and using 6 as the factor of safety, we get for the maximum, safe-working pressure, or two and one-third times the maximum pressure ever carried. Reported tests by the French builders showed a tensile strength of 59,000 pounds per square inch, with a reduction of area of 19.2 per cent. Using this in the above formula, the greatest safe pressure allowable becomes 381.5 pounds per square inch. It will be noticed that there is a difference in the reduction of area of the materials as found by the American and French tests. The reduction of area would indicate, in a measure, the ductility of the material and the facility with which it can be worked, but can have only a limited bearing on the strength of the finished structure. A more important consideration, bearing on the safety of a boiler, is the limit of the elasticity of the material; for, after having been once strained beyond this limit, its ability to resist subsequent strains is diminished. Besides considering the Shearwater's steam-drum as a simple hollow cylinder, it must be remembered that the diaphragm plates lend considerable additional strength by their stiffening influence, a fact which must be apparent. In view of the above considerations, there is no hesitation in expressing the opinion that the Belleville boiler of the Shearwater is perfectly safe for a pressure of 300 pounds per square inch. PERFORMANCE OF THE VESSEL. It is doubtful if any complete and carefully-measured data of the performance have ever been taken, as none were obtainable by the board. The machinery is well proportioned, and is capable of developing the 220 horse-power for which it was designed, provided that sufficient steam were supplied, but it is not certain that so much power has ever been realized. It is said that, under favorable circumstances on one occasion, a run of 48 nautical miles was made in four hours; the revolutions per minute were 170, but neither the coal consumption nor indicated horse-power were given. In ordinary steaming the speed, as given by the officers on board, is about 10 knots, occasionally, but rarely, reaching 11 knots, with a coal consumption of about 450 pounds per hour. No log is kept. During the boiler test, several sets of diagrams were taken from the engines-one set, with 143 revolutions per minute, giving an indicated horse-power of 132.60; and another, with 137 revolutions, 127.65. CONCLUSION. It is to be regretted that there were no means of increasing the rate of combustion and production of steam by a powerful forced draft. Under the conditions of the trial, the evaporation and rate of combustion were not greater than in boilers in common use in the naval service. The boiler steamed freely, was under easy control, and furnished comparatively dry steam. Its weight seems excessive for the quantity of steam furnished, but this is due largely to the heavy casing and brick-work, which would be proportionally less for a number of boilers placed together. The advantage of accessibility of its parts for repairs may be, perhaps, offset by extra liability to derangement on account of the large number of joints required in the fire-surface. During the trial, however, the joints were all perfectly tight, the boiler being new. This report would be incomplete without an acknowledgment of the assistance rendered and facilities furnished by the officers of the U. S. Fish Commission at Wood's Holl, and particularly of the liberality of Mr. Forbes, who not only placed the yacht and her crew at the disposal of the Government for the trial, but also supplied some necessary instruments. Very respectfully, Engineer-in-Chief GEO. W. MELVILLE, U. S. N., F. C. BIEG, Assistant Engineer, U. S: N. Chief of Bureau of Steam Engineering, Navy Department, Washington, D. C. |