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26 THE MarRINE REVIEW NOTES ON THE PERFORMANCE OF THE THOR- -. NYCROFT BOILER IN A MONITOR. - BY LIEUT. W. T. CLUVERIUS, U. S. N., MEMBER.* a ' To. have steamed 28,000 miles since commissioning, . three years ago, with nearly one-third of this time consumed in re- . pairing a turret mount at a navy yard dock, seems a fair test of the performance of the four Thornycroft-Daring boilers of the harbor defense monitor Arkansas. This type of water tube boiler has been present in our torpedo craft for several years, and trouble has been found generally in the fact that the upper rows of tubes could not be drowned and corrosion in these tubes readily set in. In the later pattern of these boilers, however, these tubes are flush with the top of: the steam drum and are drowned if the boiler is kept entirely full' of water.' This obtains'on the Arkansas, and é undoubtedly. the increased life of a Thornycroft boiler tube is due to this change in design, for on the Arkansas not a sign' of even slight: corrosion has' appeared until recently. In: fact,no tubes: had-been lost, except' once through' careless handling' of the feed' when: newly commissioned, until last month. Two tubes were lost at that time in the' vicinity of the: steaming' level, the only locality in'thée drum where the tube ends show 'any evidence of corrosion. : "Assuming that the life ofa tube depends upon 'the care nes it receives, and' that it is not affected by the forcing of the boiler within reasonable limits, the longevity of such tube may be detertiined rough inquiry into the. attention given: the boiler. 'The following is the procedure on the Arkansas, and, whether successful or otherwise, it is at least consistent : When the fires have been burned down and the boilers dis- ~-connected, the tubes are swept with a steam lance from top to bottom while there is still pressure showing in the gauge. If in port, the uptake also. This removes much of the deposit, though not any of that which has settled in the spaces where the nests of tubes contract to enter the steam drum and the wing drum. If neglected, these spaces, for a distance of nearly a-foot above the wing drums, and as much out- board from the steam drum, become entirely choked and reduce the heating surface, and therefore the efficiency, of the boiler materially. To get at this deposit, a tin scraper, together with a stiff whisk broom, is used. Each tube is 'carefully gone over and the interstices cleaned oyt. This is necessarily a-slow process, but it is time well spent. Even this does not reach properly the inner corner where the rear nests of tubes enter the wing drums; and if the furnaces are allowed to remain any length of time without cleaning it becomes | impossible to clear out these pockets without -removing the rear casing of the boiler. As a remedy it is 'suggested' that' soot doors be fitted-in the casing as in the 'front casing. 'Two such doors on each side, one just above the wing 'drum and the other vee up in the casing, would meet the reqtirements. As. regards reaching the tubes of the midile water drum, much less difficulty has been experienced. With this atten- tion in port to tubes and uptakes, the boilers have steamed freely for five days without sweeping. All of the feed water 'used is distilled on board, no matter whether taken from the -sea or the shore. The water is given frequent nitrate tests with: a standard solution at the distillers before it enters the reserve tank. The condensers receive the same test. I believe that no salt scale has ever been found in any of the four boilers. To insure an alkaline state, a small amount of sal soda is put in each main condenser every other day while underway, and in port about a quarter pound once weekly. To prevent the passage of grease into the boilers, no oil is allowed in the cylinders and but little for swabbing the rods. The dynamo engines being steepled, with low-pressure cylin- *From the journal of the American Society of Naval Engineers. der below, and running in oil as they do, some oil is drawn up the low-pressure piston rod and it finds its way to the feed and filter tank. The water in this tank is constrained to pass through three thick layers of loofa--a most satisfactory filtering agent--be- fore it reaches the feed pumps. This loofa is removed every fortnight and given a soda bath, being entirely cleansed of oil. The life of a piece of loofa is about two months. It is also used in the distiller filters with excellent results, Once each month the boiler drums are opened, cleared of zinc baskets, baffles, etc., thoroughly wiped out and inspected. A solution of 25 lb. of sal soda is then placed in the 'boiler; it is closed up, filled to steaming level and fires are started. It is boiled out for. six hours at a pressure of 50. lb. The boiler. is now blown down, opened and again wiped out. The drum fittings are overhauled, after which the boiler is closed and filled with water. Judging by the present' condition of the visible portions of the tubes--and it is impossible to determine the condition of a bent tube throughout its length--coupled with the uniform attention which the Arkansas boilers have received since in- stallment, I would submit that the period of complete effi- ciency of a Thornycroft boiler in a vessel of the monitor type, performing the same service as the Arkansas, is three years. After that, watch the tubes closely. There are two furnaces to' each boiler, and the small grate area of each (24.8 sq. ft.) necessitates a more frequent cleaning of fires than ordinarily. In free. route at sea, with the average quality of coal and under natural draft, it is often found desirable to clean one furnace of each boiler or half of the whole number of furnaces every watch. With clean coal, free from clinker or under forced draft, one quarter of all the furnaces suffices. The use of the blowers, so often demanded while steaming in squadron, through foul condition of hull or with poor fuel, has proved very trying to the furnace linings. Not only do the walls require constant patching, but the casings themselves suffer eventually, and the least warping of the front casing produces leaky furnace-door frames and also endangers the front-lining brickwork. In common with all boilers of this type, the proportion of heating to grate surface is large (47.3 to 1), and the gases well baffled. The Arkansas can. steam, under normal condi- tions of hull and sea, 2,700 miles-at a ten-knot speed. Probably the most interesting comparison in the operation of these boilers is that of their performance with a clean hull and with a foul one, other conditions being equal. A, is a sixty-hour trial during a run to the West Indies, clean hull, natural draft. B, is a sixty-one hour trial on the run north, very foul hull, natural draft. A Distance: tun, knots: 3.35. ee eee es 621.6 oan 2 Average speed, knots. 3... 0. ke es « 10.36 9.8 a Feveuions (2) oe ea 150.1 156.4 Revolutions per knot... .... 131g ae ots 16. (coal ner day, this rate, toms. . 2s. 5 6... oe 31, Al. Worcs per tOm Of COdl. 2... ec we eee 8. 5.7 Steaming radius. milés.........ss.ee5e0 2,672. 1,903.8 This shows a 25 per cent increase in the daily coal con- sumption due to foulness alone; so'that this factor, together with a heavy head sea, most of which is shipped, becomes a serious question in a monitor. Following is a table which may also be of interest: A B @ Revolutions per minute..... 206%. 107.1... 1601. 1867 Speed per hour, knots...... 13.5 12.7 10.7 11.6 Total horsepower developed *2,500 1,826.6 2,080.4 2,218.9 Pounds of coal per hour.... 7,200 6,720 5,471 6,850.5 : Mo sa ft. wrate Suipace ... ..; 30.4 33.9 27.5 34.6 (6 ae ta 2 per hour sk). 2.9 3.6 2.6 31 A, is the best hour's run the ship has made, hull clean. *A pproximated.