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58 ' WARINE REVIEW Reduce Fuel Bill (Continued from Page 16) full content at any temperature before placing on board and apply the cor- rection for the observed temperature which has to be done in any case. Referring to Table I the examples are all too few and comprise only these which are defintely certain. Others may exist in the second group but the fact is not, at least to the writer, clearly established. The table is condensed from trial data to which some reference may be made later. There are three examples, of two different types, in th2 water tube class and two in the scotch. A third scotch boiler ship in which actual weights are given is rejected because the calculated rate seems too high with the stack temperatures shown. It may be said here that while evapo- ration from and at 212 degrees per pound of combustible is of course the true basis of comparison, yet the method of ascertaining the weight of combustible in all the tests is open to very serious errors. This is to deduct the weight of moisture and refuse from the weight of coal as fired and the remainder is con- sidered as combustible. However the refuse frequently contains a consider- able amount of only partially burned fuel so that while. the apparent weight of combustible is thus reduced a considerable proportion of the heat value of the actual fuel has passed into the boiler so that a misleading evaporative figure is thereby es- tablished. A further error is in- troduced if the refuse is not perfectly dry when weighed and this feature demands the closest attention on the part of the observer. These things are true with either, or any, type of boiler and sometimes lead to rather curious results. Thus ships WT1 and WT2 exhibit rather high refuse per- centages and yet both are fitted with mechanical stokers. The other three ships are hand fired. WT1 with the highest refuse is using the same grade of coal (Pittsburgh mine run) as Sl, 82 and WT3. WT2 is using a slack, evidently of low grade, as indicated by the b. t. u. value, nevertheless one is inclined to look for decided offsets through the use of stokers. Hence comes about the _ curious anomaly that the lower the com- bustible values the higher the effi- ciency when based on combustible, as any one with sufficient curiosity may demonstrate. It is not to be under- stood that this is confined to any type of boiler; among the reported trials of scotch boilers is an instance where the moisture is reported at 13.3 per cent (which is probably a fable) and ash at 16.1 per cent or a combustible value of 70.6 per cent. It would be interesting to examine 87 pounds of coal with 13 pounds of water added to it. The dry coal efficiencies of WT1 and WT3 are missing because no b. t. u. values for the fuel are supplied. So far as Table I is concerned therefore the comparison resolves itself into lines 7 and 8. It is admitted to be a somewhat narrow base but lack of dependab!e data prevents its exten- sion. There is however a very broad field concerning which there is a consider- able amount of information which is ° © fav! [usalio7) — [+67[s09] dependable in some respects but in- volves other factors besides boilers. Numbers of ships with both types of boilers have undergone trials where the only data of interest here lie in the indicated horsepower and the amount of fuel burned in terms of pounds per indicated horsepower. Metered water measurements. are given in numbers of instances but are rejected for reasons already stated. Ash and moisture are given in many instances and may or not be reliable. On the whole it is believed that the February, 1927 results of their omission will average out. The indicated horsepower and the fuel weights may be accepted as fairly accurate and thus in a large group may be said to reflect the in- fluence of the type of boiler on the ship’s performance. The fuel per indicated horsepower is to be under- stood as for all purposes. To assist in making comparison the table is separated into two groups, classified under triple engines and quadruple engines. The data are condensed from trial reports derived from builders and owners and in some instances from trials conducted by outside ob- servers of unquestionable competence. The author has excluded all data derived from trials in which he took any part or which were conducted under his direction. Some of the in- formation is confidential and the identity of all vessels has been there- fore withheld. The table does not of course ex- haust the list in any class nor even of ships from which figures more or less uncertain are available. Triple en- gines with water-tube boilers have been few in number and while quad- ruple engines with scotch boilers form a fairly large class reliable figures are scanty. All these ships are bulk cargo vessels and working under similar conditions as to fuel which, it should be kept clearly in mind, varies as to quality not only as be- tween ports but also as_ between different fuelings in the same port. The figures seem to speak for themselves. The quadruple engine contributes its share of responsibility but this point will be taken up later. Apparently the scotch boiler has the best of the argument by quite a wide margin. This may seem excessive but if we turn back to Table I for a moment we see that the difference there in evaporation from and at 212 degrees per pound of dry coal (line 8) averages nearly 23 per cent better than with the water-tube. It is true, as already said, that the examples in Table I constitute a very narrow base, but if we now look at Table II we see these same two ships reappear as 1 and 2 and we see that their fuel per indicated horsepower averages 1.88 and we see further that several ships in the same column are close up, two in fact better than S2. On the other hand the three water-tube ships of Table I are among the very highest as to fuel per indicated horsepower in Table ITI To assist in visualizing the relative performances the figures from Table II are plotted in chart form in Fig. 1. (Continued on Page 62) ee ee ae ee