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Are Lake Vessels Efficient? Some Comments on a Recent Article—A Reduction in Operating Cost Is Possible with Modern Pro pu Isive and Auxiliary Machinery sels’ Fuel Bill,” published in Ma- RINE REVIEW in four parts, be- ginning in the February issue, Henry Penton has brought up some _ inter- esting questions, and, while one must read the article with the respect due to his experience, it seems to embody largely an expression of opinion rath- er than a statement of definite proofs of the questions raised. Not in a con- tentious spirit but in the interest of better marine engineering practice it may be worth while to look into some of the points brought out by Mr. Penton. It is to be regretted that so few real boiler tests have been made on lake vessels. A test which stops at weighing the water and coal without striking a heat balance can hardly be called a real boiler test. The tests which Mr. Penton shows in Table I have only gone half way and the boiler is held responsible for the com- bustion, a factor over which the type and design of the boiler can have little control. Combustible in the ash and the CO, content of the flue gases are largely a matter of having a good fireman and this human fac- tor can easily account for 5 per cent in the efficiency of the boiler. If we neglect to take CO, readings and to weigh the ash and determine the quantity of combustible in the ash, we can only assume these factors to equalize each other in making a com- parison. We then have a _ possible error of at least 5 per cent. | HIS article, “Reduce Lake Ves- Two Installations Not Comparable The water tube boiler WT, is com- pared with the two scotch boilers S, and S,, both of the latter having air heaters. The temperatures of the gases leaving the boiler in these two cases are not given, but these temperatures have been reduced to 255 degrees Fahr. and 265 degrees Fahr. respectively, through the air heater. The heat represented by this drop in temperature has been used to raise the temperature of the air supply from say 80 degrees Fahr. to 298 degrees Fahr. and 308 degrees Fahr. respectively, this heat being returned to the boilers. What we really have in tests S, and §S, is not the boiler The author, gineer attached to the staff of the ‘Fransportation Co. is an en- Bradley R. C. Stanbrook, BY R. C. STANBROOK efficiency, but the combined efficiency of boiler and air heater. This effi- ciency is then used in a comparison to the detriment of the water tube boiler using unheated air. It is a common practice to use air heaters or economizers with water tube boilers and if this type of equipment were used with boiler WT, to bring the stack gas temperature down from 445 degrees Fahr. to 298 degrees Fahr. we would gain about 3.5 per cent making the watertube boiler compare favorably with the scotch boilers. Should Determine B.t.u. in Coal In tests WT, and WT.,, the b.t.u.s of the coal have not been determined and the only reason the tests have been in- cluded seems to be to show “water per pound of coal from and at 212 degrees Fahr.’”’ Pounds of coal have little interest for the engineer un- less he knows the b.t.u. and, if the owner is buying coal without some check on the b.t.u., a revision of his purchasing methods should promise some savings. In Table II Mr. Pen- ton condemns water tube boilers on the basis of “pounds of coal per indi- cated horsepower hours for all pur- poses.” Again we do not know the b.t.u. of the coal used in the various tests and it is unfair to make com- parisons unless one assumes that the averages will give reliable results. So many factors enter into “coal per indicated horsepower for all pur- poses,” that one should hesitate to condemn any one piece of equipment without testing separately for the efficiencies of the various units com- prising the installation. It would seem that the question of scotch versus water tube boilers at 175 to 225 pounds pressure per square inch and triple versus quadruple ex- pansion engines at about 3000 in- dicated horsepower will continue to be an open one. Use Efficient Surface Condensers With regard to surface condensers, it is clear that considerable improve- ment could be made over any con- denser which gave a difference in condensate temperature and the the- oretical temperature due to the pres- sure of 20 degrees Fahr. Some con- densers have apparently been built MARINE REVIEW—June, 1927 with the idea of getting as much cool- ing surface in as small a space as possible. A well designed condenser with good distribution of the steam, ample steam lanes and effective air extraction, should not give a tem- perature difference of more than 10 degrees Fahr. under operating condi- tions. This is equally as good as a jet condenser, where one observation of conditions will usually show a hot- well temperature of 125 degrees Fahr. with 24-inch vacuum, a difference of 15 degrees Fahr. Mr. Penton’s figure of 3% per cent fuel saving in favor of the jet condenser is fictitious. The quantity of water required to condense a given amount of steam is indepen- dent of the condenser and this water has to be pumped whether by a large air pump as in the jet, or a separate circulator as in the surface con- denser. There is some difference in the friction head in favor of the jet condenser represented by less than 4 horsepower for a 2500 indicated horse- power engine. Turbines and Reduction Gears A modern, well designed’ surface condenser does not require much up- keep and it certainly is good to have the vacuum when handling the vessel. The extra investment is not large if the cost of an adequate purifier is added to the cost of the jet condenser and will be easily repaid by having clean feed water for the boilers. The impression one gets from the article under consideration, is that the marine engineering of 25 years ago, cannot be much improved on. From a survey of the more recent lake vessels, one would be inclined to agree. There have been few improve- ments except in minor details. This seems strange when we consider the progress which has been made ashore where we now have modern electrical power plants with their kilowatt hour per 14,000 b.t.u. The turbine is given scant con- sideration and the subject is dis- missed with the statement “the tur- bine is absolutely dependent upon su- perheat.” It is interesting to note that many turbines have been in- stalled to utilize the exhaust from existing reciprocating engines, and have developed when working with 28%4-inch vacuum, as much power 21