Sept. 26, 1889.] 



FOREST AND STREAM. 



197 



THE THORN YCROFT WATER-TUBE BOILER. 



ATTENTION has lately been drawn to this boiler by t he request 

 of the Herreshoffs that they be allowed to use it. in the 

 new torpedo boat tor the U. S. Government now under construc- 

 tion, in place of their own boilers. The following paper, for 

 which we are indebted to Knginccrinti, was read by Mr. J- I). 

 Thoinycrnft at the last meeting of the Institute of Naval Archi- 

 tects: 



In modern warships the weight to be carried is an ever iticreas- 

 ir-g source of difficulty. The essence of a skillful design is (lie 

 combination of great powers of offense and of defense, of sped 

 and coal endurance, in a limited displacement. In the ironclad 

 of to-day, evidence may be seen in every part of the struggle of 

 the (lesig&er to reduce the weight of his element* without im- 

 pairing the efficiency of the structure. Forced to increase the 

 thickness of his armor, he covers with it only a small portion of 

 the hall, and he hardens the face of his plates to increase tin; 

 resisting power of a given weight of material. The structure of 

 the hull has been elaborated uutil the amount of material has 

 been reduced to a minimum consistent with safely. The weight 

 of the guns has been reduced, 1 am inclined to think, quite as 

 much as is desirable when the amount of the charge is consid- 

 ered; and the engines, like the guns, have had their pressures and 

 velocities increased until progress in these directions appears to 

 have reached a limit. In the boilers, however, there is still much 

 room for reduction of weight, not only by economizing material 

 but also by economizing fuel. Mr. Sennett's paper, last year, 

 shows how strong is the pressure brought to bear upon the engi- 

 neering department with a view of saving weight in the boilers. 

 His answer has been, reduced test pressures and reduced thickness 

 of material. Economy of fuel in steam boilers depends greatly 

 on the amount of heating surface that can be allowed for a given 

 Evaporation. If we can estimate the weight of a unit of heating 

 surface in different classes of boilers, it becomes a very simple 

 matter to calculate the comparative weight of boilers for a given 

 economy of fuel. On the other hand, for a given weight of boiler 

 we can estimate the saving in fuel, or the increase of power, due 

 bo a change from one class to the other. 



some experiments were made at Portsmouth two years ago 

 having a direct bearing on this subject. By an evaporative trial, 

 at natural draught, of two boilers, the on- locomotive and the 

 other water-tube, t he heating surfaces of which were in the ratio 

 01 1 to 2$, it was found t hat in the case of the lat ter hoiler the 

 rate of evaporat ion could be increased in the ratio of 1 to 8JM with 

 the same economy. It follows that a water-tube hoiler will evap- 

 orate a little more wafer per foot of surface than a locomotive 

 whi n working equally economically, and, therefore, under these 

 conditions, the weights of the two types will be proportioned to 

 one another as the weights of a unit of beating surface. The 



weights of hoiler and water and fittir 

 face of the lot omoiivea 



were 



;'.Yiilhs. 



and 9.61 lbs 



wate 



r-ttihe 1 



lotler and \\ 



asal 





ive boiler a 



tice \ 



ve pre; 



Br to make 



the 1 



oil- ra i 



ess bard ox- 



face 



for a 



given quail 



meat 



s bette 



r economy 



upon 



the ho 



lers. 



_ per foot of heatin^ . . 

 ter-tuhe boilers tried at Portsmouth 

 respectively. The weight, therefore, of a 

 iter, working at the same economical rate 

 id water, will be loss than half. In prae- 

 smaller reduction in weight, and to work 

 giving a larger allowance of heating sur- 

 ety of water to be evaporated. By this 



Whereas the common wind pressure for locomotive boilers in 

 torpedo boats is from •I'm. to 5in. of water, we do not usually ex- 

 ceed lj£in. to 2in. with the water-tube, and a corresponding re- 

 duction could doubtless be made in war-ship practice. The7 fol- 

 lowing figures wil show the amount of the saving in weight: 



Indicated 

 horse power. 



Indicated horse power per ton weight of water-tube boiler, 

 including all littings, mountings, water pipes, donkey, 



spare gear and funnel 63 



Locomotive boiler of same power in a torpedo boat IS 



Locomotive boiler in the latest English torpedo catcher. . . t;> 



Boilers of H. M.S. Anson 21.3 



Boilers P. and O. steamers 16|(i 



The boiler has other qualities which render it. particularly suit- 

 able for warships. In audition to the saving of fuel due'lo the 

 greater economy, the power of getting up steam in a short inter- 

 val of time must tend to further saving, for when it takes a long 

 time to raise steam it must be Kept up continuously, if there j« a 

 probability that it may be wanted with onlv a notice of an hour 

 or two. Willi the power to get up steam quickly, it would be suf- 

 ficient to keep steam in one holier, for Che purpose of starti a" 

 auxiliary engines and warming the maiu engines. It has been 

 found that steam can be raised in from 15 to 20 minutes without 

 risk of injury, and forced firing has never caused leakage of the 

 tubes. 



Tne water-tube boiler consists simply of three cylinders lying 

 parallel to each other, the smaller being at the base of the struc- 

 ture, and t he larger one at the top. (See Fig. 1.) These cylinders 

 are connected by means of two large tubes at the firedbor end 

 and are stayed at the opposite end by a triangular frame. A 

 further connection exists between the top and bottom cylinders 

 in a great multitude of small tubes. These are the steam-gene- 

 rating tubes. On looking carefully, it Will be noticed tba : : i f 

 inner row of tubes, forming what would be the crown of the firebox 

 and the outer row, forming what would be the shell in an ordinary 

 boiler, are, by means of a very simple alteration at their end* 

 made to lie quite close together, so that none of the products of 

 combustion can pass between them (Fig. 3). The lower part of 

 the upper cylinder is thus protected from the direct action of the 

 heat. The tubes are fixed in the cylinders by expanding in the 

 ordinary way, and an outer casing of thin steal covers the whole 

 In the upper half of the upper cylinder a curved baffle-plate with 

 serrated edges is fixed to protect the steam pipe, and effect the 

 separation of the water and steam. The hrebarsare disposed at 

 the base of the boiler, and between the two lower cylinders They 

 are surrounded by firebrick slabs, which act as protectors' to the 

 lower cylinders, and as bridges over which the flame most pa«s 

 on its way to the chimney. 



When steam is required, the boiler is filled with water up to 

 nearly the middle of the upper cylinder, and the fire is lighted 

 The products of combustion pass ovr Mr ...... , : 



through tne spaces between the lower ends of the generating 

 tubes, into the spaces between the tubes, and along tnem to the 

 upper half of the upper cylinder, whence they pass to the funnel. 

 In addition to the heat absorbed by the gases a great amount of 

 radiated heat is received by the tubes forming the crown of the 

 furnace. The heat absorbed by the tubes is at first only commu- 

 nicated to the small volume of water within them, so that 

 the density of the water is rapidly reduced. At the same 

 time the two large tubes which connect the upper and 

 lower cylinders are filled with water of the original 

 density, thus more than balancing the weight of the 

 contents of the generating tubes, and causing rapid circulation. 

 The discharge from the tubes into the upper cylinder is a mixture 

 of steam and water, and these elements are separated as thev 

 flow over a curved baffle-plate, which is placed immediatelv under 

 the openings of the tunes, and incloses a considerable space above 

 the water surface protected from spray, and from which the 

 steam is taken. 



The absence of leakage may be briefly explained as being due to 

 the facts that the. tubes can expand freely, and that their connec- 

 tion with the upper and lower cylinders are not exposed to the 

 heat of the fire, while in fire-tube boilers the part of the tube ex- 

 posed to t he most severe heat is its junction with the, tube plate 

 around which there is no water to cool it. 



Opinions have been expressed that this boiler will have but a 

 short Me. Opinions on such a matter are not of much value, and 

 the author thinks it will be of interest to the institution to learn 

 how the boilers, of this type, which are already at work, have 

 stood the test of time. The first one was made for the Congo Mis- 

 sion steamer Peace. The vessel was tried on the Thames in 188 ! 

 then taken to pieces, the boiler included, and re-erected in Africa 

 by the Rev. Geo. Greufell, with black assistants only. She com- 

 menced work on the Congo in the spring of 1884, and has per- 

 formed continual, service since. The last, news we had of her was 

 contained m a letter from Mr. Grenfell dated the 18th &t Septem- 

 ber last. He says: "The boiler itself is doing splendidly, and we 

 have no difficulty in keeping up steam sufficient for 400 revolu- 

 tions; in tact, quite steam enough for any purpose, and when 

 head to wind oiteii too much." 



The next boiler was fitted in a second-class torpedo boat for the 

 British Navy, and tried eariy in 1886. it has therefore been at 

 work tor about three > r ears. I obtained permission from the 

 Admiralty to remove some of the small tubes for ascertaining 

 their condition. These specimens were cut out last week, and are 

 exactly m the condiiion in which they were taken from the boiler 

 In examining them 1 was exceedingly pleased to find thai the 

 deposit it them was so very small in amount. It appeared possi- 

 ble that this boiler might fail, from the tubes becoming obstructed 

 by deposit, and as it is impossible to gain access to much of their 

 interior, this would have been a very serious drawback. Iam 

 not aware that the boiler from which these tubes are taken has 

 been treated with any special care; the surface condenser is of 

 the ordinary kind, and is not specially made to prevent leakage 



A few of these tubes, however, are not in such good condition 

 as 1 had hoped; oxidation seems to have taken place to a slight 



THE THORN YCROFT WATER-TUBE BOILER, 



extent within them, and the external surface of those taken from 

 the outer rows has been very much rusted, aud seems to indicate 

 that these tubes have been wet for a considerable period. This is 

 corroborated by the fact that the plates forming the external 

 casting are also decayed in places. It is most satisfactory, how- 

 ever, to find that the tubes in the flue, and also those forming the 

 firebox, are in most excellent condition. The blue scale is still 

 visible on the outside, and the parts of the tubes exposed to the 

 most intense heat do not show the least trace of injury from the 

 fire. 



The next examples are the boilers of the Ariete and Rayo. It 

 will be remembered that an exceedingly high speed was attained 

 by these vessels, due largely to the lightness and steaming power 

 of the boilers, of which each boat had two. They were delivered 

 to the Spanish Government in August, 18S7. Very soon afterwards 

 newspaper reports appeared as to defects having manifested 

 themselves, and it was stated that the boilers were condemned, 

 and were to be replaced by others of locomotive type. We had 

 no communication made to us officially concerning these alleged 

 defects. 



Seeing in the newspapers an account of certain maneuvers in 

 which these and other torpedo boats were engaged, where it was 

 stated that one of the boilers of the Ariete was disabled, we applied 

 to the Minister of Marine for permission to send an engineer over 

 to examine the boilers, and to put right any defect which had 

 arisen. After much delay this was granted, and our engineer 

 reported as follows: 



"The work of removing pipes, casing, etc., was commenced 

 March 15. On removing the front and back plates of boiler cas- 

 ing, all the small tubes were found covered with a coating of soot 

 from 5^in. to 3 16 in. thick. I then caused the side casing to be 

 removed; when this was done the lower parts of the casing (ad- 

 joining the coal bunkers) weTe found wasted away, caused by 

 small coal, ashes and soot being allowed to accumulate to a depth 

 of about 5in., the steam-heating gear pipes being imbedded and 

 partially destroyed. 



"The front frame plate carrying the ashpan doors was then 

 removed, and I found the ashpans firmly fixed in a bedding of 

 small coal and soot which had been allowed to accumulate; this 

 had to be dug away before the ashpans could be removed, and 

 through this accumulation it has to some extent corroded the 

 sides of ashpans. On going inside the firebox I found the Are- 

 bricks much damaged, and they have been in this condition for 

 some time; those on the port side will have to be removed. The 

 center firebrick on the inside of end casing, nearest the safety 

 valve end of boiler, is missing, and from the crumpled appear- 

 ance of the plate has beeu in this state for some time. The inside 

 of separator tube aud collector tubes are very fair, no appearance 

 of pitting being discernible, although the collector lubes have a 

 deposit on the bottom of %ux. of lime, etc. The separator dash- 

 plates (zinc) have wasted in their thickness from %xa. to s i e in. on 

 the part that has been in the water, while the upper parts have a 

 great deal of sediment fixed on them. The zinc bars in the col- 

 lector tubes are but. slightly worn. 



"I have examined the safety valves and stop valves, and these 

 are in a very fair condition. This day I have tried the small 

 tubes with water, and have discovered one tube in the row marked 

 I, or the second row counting from the top center of separator, 

 and it is the eleventh from the safety valve end of boiler; this is 

 the only one I have discovered, and it is caused through a small 

 hole in tube of about %in. in diameter. I propose to draw this 

 tube and refit a new one, to remove all sediment from the col- 

 lector tubes, clean zinc dash plates and bars, refit new firebricks, 

 well cleanse the outside, of small tubes from the soot, and remove 

 the damaged parts of side casings and fit strips of plate 8in. deep 

 to take the place of damaged parts. 



"I would add that there is nothing in these repairs, excepting 



the damaged tube, but what could have, and should have, been 

 done by tne stokers belonging to the ship, but which, from the 

 total neglect the boiler has received, has very seriously impaired 

 the efficiency of the boiler, until the neglect is rectified, in ref- 

 erence to tne damaged tube, there are a number of special plugs 

 supplied with the ooat for the purpose of putting out of use any 

 detective tube or tubes. Had this been applied— and the applica- 

 tion of it is very simple— no annoyance would have been experi- 

 enced, except instead of 918 tubes there would have been 917. 

 From the general appearance of the boiler and fittings, it shows 

 it has been greatly neglected, for in addition to the steam clean- 

 ing gear, there are brushes supplied to assist; these have not been 

 used, nor have the end plates been removed for this purpose nor 

 for inspection, since the ooat left England." 



The next vessels in order were tne Danish torpedo boats Stiiren 

 and Soloven, delivered in 1887. Since then we have supplied 

 water-tube boilers in ail the new torpedo boats built tor that Gov- 

 ernment, and are now replacing tne locomotive boiler in a ooat 

 5}4 years old, with two water-tuoe boilers. 



Careful experiments have recently been made by Prof. Kennedy 

 on one of these boilers, in order to ascertain the evaporative 

 efficiency at different rates of working. The best result was with 

 natural draught, when the evaporative duty reached lo.tlbs. of 

 water per pound of coal, from and at 213°. Tne Calorific value of 

 the coal, as determined by analysis, was 15.411bs. per pound of 

 coal. The efficiency of the boiler with natural draugnt was, there- 

 fore, 87 per cent, of the theoretical evaporation, wnich we have 

 reason to believe is the highest on record. 



MIRAM1CHI Y. C. 



THE last race for the Miller and Call-Noonan cups was sailed 

 on Sept. 12, the course being trom .Newcastle to Chatham 

 and return, 10 miles. Wind, deau ahead on the first leg. Kilbride 

 lead from the start, with Kittock second, Blondy third, and 

 fedora (schr.) last. When oft Chatham Fedora was knocked over 

 by an unexpected pulf or great force, the first of the day, and re- 

 fusing to luff, tilled and aanii in BUtt. of water. "Let go" sheets," 

 ordered the skipper, Vice-Corn. Stewart, as he jammed the helm 

 hard down, but the crew of 4 leaped upon the windward rail and 

 seized lore aud mam rigging. Dir. Stewart went down with the 

 ship, nelm down and sheet in hand, and had to disentangle some 

 ropes that floated up around his tegs before he could get up. He 

 reached the surface Lift, from the masthead, to winch the crew 

 were clinging, and, though he dad never swam a stroke uefore, 

 swam on me water and under the water, against the tide to the top 

 mast stay. Clear grit andcoolness won agaiust the heavy odds. 

 The judges' steamer, Derby, tooK the snipwiecked yachtsmen off, 

 none the worse tor the bath. Kilbride won, and lLondy took 

 second place on time allowance. Mr. Secretary Watts's ooat cap- 

 tured the Call-Noonan cup. Tne lollowing is the record: 



PI R.ST 01, ASS. 



Elapsed. Corrected. 



Kilbride, J. C. Miller 1 59 33 1 59 33 



Kittock, Jas. Miller 2 04 42 2 03 50 



iilondy, W. R. Gould a 08 22 2 03 33 



Fedora, J. L. Siewait Capsized and sank, 



siseoiai class. 



Mackerel, Geo. Watts 2 53 45 



Squirrel, Thos. Crimmen 2 59 04 



Gommodore Milter has won his own cup twice, and Secretary 

 Watt nas won the Call-Noonan cap. The next unci last race of 

 the season will be for the Vice-Commodore's pennant. 



LAWLEY'S YARD.— Messrs. Lawley & Son will put in new 

 tools this fall, including a plant for composite construction, 



