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1899] MARINE REVIEW. | 13 increased (probable) available power; increased ease of protection; in- creased handiness when partly disabled; smaller water-tight compart- ments; smaller propellers; more efficient propellers; less peripheral speed of propellers; less screw friction; increased revolutions of engines; de- creased loss from cavitation, the word being used in its broadest sense; increased efficiency of the screw working in the following wake; decreased danger to propellers in ramming; decreased danger to ship that is rammed or torpedoed; shorter propeller shafting; decreased racing of screws; freer design of stream lines; freer access of water to screws; in- creased piston speed and economy; decreased total size of cylinders; de- creased weight of machinery; decreased condensation in engines at all-- especially at low--powers; adaptability to light draft; high ratio between stroke and diameter of cylinders; less glacis plating required; ease of pro- peller design; latitude of engine design; great gain in economy at low powers. Disadvantages--Greater number of parts; greater number of valves and pipes; greater number of auxiliaries; increased engine room force; loss of power due to drag of idle screw; with center engine alone used, the loss of the tactical advantages due to twin screws. In the case of the proposed system of triple screws with small wing engines the only disadvantages set down are that there would be two sizes of engines in the same ship, increased cost of building and increased num- ber of spare parts to be carried, while the advantages claimed are: The arrangement fits the ship; ease of installation and design; great gain in economy at all speeds; tactical advantages of twin screws economically re- tained; engine room space reduced; powerful center engine has a most economical screw working in following wake; vibration minimized; loss from drag of screw minimized, one screw only being dragged; small size of working parts; two independent plants, each capable of economical propulsion up to 15 knots speed; small size of working parts with maxi- mum ease of repairs. CRITICISM OF ENGLISH EXPERTS. In discussion of the paper, both Mr. A. E. Seaton and Professor Biles said that it would have been more satisfactory if the author had stated the data upon which he arrived at many of his conclusions. In Mr. Sea- ton's opinion Commodore Melville had stated his case most ably, but had stretched it a little further than was necessary. He had given fullest value to the advantages that followed the use of triple screws but had minimized the disadvantages. The nuisance that arose from the engines not in use had been dealt with lightly. If three engines were to be fitted, the center screw should have more power than the wing screws, but he would suggest that the center propeller should be. two-bladed, so that it should be shielded by the stern-post when not in use and the drag would be less. In conclusion, he would say that the paper would form a most valuable addition to the transactions of the society, for the author, at least, had put the various points relating to triple screw propulsion in a light that perhaps few had seen it before. : Professor Biles thought the paper was open to criticism that the au- thor had tried to prove a little too much, but that was due to his generous and enthusiastic nature, which was also the cause of so much of his suc- cess in life. His triple screw ships might be looked on in this way. He had taken a twin screw ship and divided one set of engines into two parts. There were, however, twin screw ships both in British and in the Ameri- can navy which had two distinct sets of engines on each line of shafting, and it might be said, therefore, that the Commodore had taken a four- engine twin screw ship and knocked two of the engines into one. In any case the advantages claimed for the bigger engine did not all apply to the whole of the machinery, but only to 50 per cent of it. It was easier, how- ever, to get in three propellers than two on a given draught. The author had said that with three screws a better performance was obtained at sea in bad weather than if two were used. What the meeting would like to have 'had would have been the facts on which this statement was based. Sir William White, director of naval construction, said that the sub- ject of the paper was one in which he had taken the keenest interest throughout his professional career, and he hailed with gladness any op- portunity of getting fresh information on the question. Some members might remember that twenty-one years previotsly he had read a paper in which he strongly recommended twin screws, not only for the purpose of affording a shallow draught design of vessel, but also for ships of deep draught. At that period the suggestion was not a popular one, but time had justified it. His excuse for recalling this earlier paper of his own was that it showed he had an open mind on the subject of multiple screws, and it would form a fitting preface to what he had then to say. There was a good deal of difficulty in dealing with a paper such as Commodore Melville had presented, because it was full of opinions, of speculations, and of arguments, but contained very few facts. When he heard the paper was coming he was delighted, and said, "Now, at last, we are going to have from the best authority the facts about the Columbia and Minneapolis." If, however, experiments had been made with these ves- sels, their details were not recorded in the paper, and there was, therefore, insufficient data for fortifying opinion. In an analysis of the performance of a steamship, to arrive at her efficiency, there was wanted a very great deal more than the author had given. Commodore Melville had said that 200 ships had been tried, but the speaker would like to know how many of these were triple screw ships. He thought that he had a fair knowledge of what trials had been made with vessels of that class and, so far as he knew, they were comparatively few. He was afraid that the deductions contained in the paper were built up on a very slender basis. He appeared before the meeting in an unusual position. He knew more than he was able to say, that was not a usual condition, but it arose some- times. He had knowledge of experiments, but 'the could not furnish the facts, as they were given him as personal information only. The paper said that three screws led to economy. He knew of no facts supporting this statement. The paper also recommended a third arrangement of triple screws in which there would! be small wing engines with the large engine in the center. In Russia the three-screw ships, however, had large screws at the sides. There was material information in the paper in regard to the waste work of revolving an idle screw. The author had taken a vessel of 12,000 tons, 28,000 horse power, and 22 knots speed. Now, it was evident chat was not an American ship, and it would be in- teresting to know what vessel it represented. Again, triple screws were recommended by the author as a necessity on account of a 24-foot draught, but he would undertake to produce a most effective twin screw vessel of the character indicated upon that draught. Speaking generally, the di- rector of naval construction said that it must not be understood he alto- gether condemned triple screws, but he was of the opinion that the con- ditions laid down in the paper did not bear out that they were yet demanded. From what had been said, he was under the impression that Commodore Melville had not introduced in his analysis the results of model experiments. Naval architects were, however, under the greatest obligation to such sources of information, and found they were constantly borne out by actual trials which they had foreshadowed, and in working out results they had found it of advantage to come back to the model screws. In regard to the utilisation of the frictional wake, upon which the paper dwelt, he would point out that it was quite possible to speak of tendencies, but what was really wanted was the actual aggregate result. For instance, the late Mr. Froude had at one time favored putting the single screw far aft, to reduce the augment of resistance, reasoning on tendencies he had observed; but on experiment it was found that the balance of advantages was in favor of the ordinary arrangement. As a matter of detail, he would have liked to have seen a more exact state- ment as to the space occupied, not only by the engine compartments in -- a triple screw ship, but by the shaft passages. The stowage of ammunition was a problem that had to be solved in the design of all warships in the British navy. For well-defined reasons they distributed the ammunition as equally as possible between two ends of the ship, but with the three- shaft passages difficulty might arise. It was a detail which showed that one cannot discuss warship machinery from the point of view of efficiency alone. He trusted that what he had said would not appear to overlook the obligation the institution was under to Commodore Melville for the paper he had contributed, and if there were further information at his-- | the author's disposal, and if he were at liberty to give it, it would be a most desirable thing that it should be included in the transactions of the institution. The speaker had always thought that if we go on progress- ing as we have done in the design of engines and propellers, and if they remain based on the same general principle upon which they are now designed--if there were no radical changes thrusting existing practice on one side--then we might come to triple or other multiple screws. But as matters stood he did not think that Commodore Melville had made out his case. ; GRAIN BILL OF LADING. A circular letter just sent out by Secretary C. H. Keep of the Lake Carriers' Association, deals with the meeting of the executive and bill of lading committees of the association in Cleveland. On the 11th inst. the proceedings of the Buffalo conference, March 8.and 9, having been duly considered, the Lake Carriers' Association unanimously agreed upon the following action: First. Each vessel owner may, if he so desires, at the time he char- ters his vessel, provide for an individual consignee at lake destination,_ and he may stipulate that if his vessel is sent to more than two elevators to load, the extra service shall be without expense to the vessel. It is believed that delays at ports of loading may thus be remedied to a great extent. Second. The following provision should be included in all lake grain bills of lading. "If the grain covered by this bill of lading is consigned in care of a party at destination of vessel, then, unless the original of this instrument is there presented for cancellation on or before arrival of ves- sel, delivery to the party in whose care the grain is consigned herein, shall be a good and valid delivery." Third. The Lake Carriers' Association accepts the offer of the com- mercial exchanges tendering the services of their respective boards of. arbitration without expense to the Lake Carriers' Association, to hear and decide any claims the association may desire so heard and decided, in respect to any exceptional detention for which the lake carrier deems it just that demurrage should be paid by the party or parties responsible for such detention, or in respect to any exceptional grain shortage for which the lake carrier claims he should be relieved from liability. Fourth. The Lake Carriers' Association will appoint a committee of three of its members, resident in Buffalo, to act in consultation with the committee of control, provided by the Western Elevating Association, in securing prompt dispatch in unloading grain vessels at the port of Buffalo. Fifth. The grain trade having objected to the shortage clause which the Lake Carriers' Association proposed to insert in the lake grain bill of lading, upon the ground that the commercial value of the bill of lading for collateral uses would be impaired, the association has decided not to insist upon the use of the proposed clause, but to allow the existing short- age clause to stand unchanged until the close of the present lake season. The Lake Carriers' Association then hopes to present a definite and rea- sonable shortage provision, that will not be subject to objection by the grain trade upon the ground of uncertainty in use. Sixth. No clause providing for the payment of demurrage will be inserted in the lake grain bill of lading this season. The detention clause proposed at the Buffalo conference as a_ substitute for the demurrage clause, will be modified in consultation with the counsel of the Lake Car- riers' Association, so as to express correctly the practice which it is understood will, by mutual agreement, govern the unloading of grain cargoes at grain delivery ports this season. The secretary of the Lake Carriers' Association will then submit the detention clause, as modified, to each vessel owner for vote as to the advisability of inserting said clause in lake grain bills of lading after a named date. Seventh. It is understood that the grain trade, rail carriers and ele- vators, will co-operate in every reasonable way to correct abuses in the ma'ter of shortage and detention and to secure dispatch to vessels at ports of loading and unloading.