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16 TAE MARINE REVIEW which met the approval of the committee in both houses of congress. I quote a few words from their report: " 'The American shipping in the foreign trade has been for forty or fifty years the only American industry ex- posed directly to foreign competition that has not been protected by the government. There is no need to look beyond this one sentence for the explanation of the hard fact that this one American industry has halted and shrunk and while all others have made prodigious increase. " 'The American merchant mazine is essentially a floating factory which is built and maintained on the American wage rate but there is this vital difference that while the land factories are covered by national protection averag- ing almost 50 percent, these floating factories, the few that. are left, work up and down the ocean without any protec- tion whatever save that granted to a few steam lines by the postal subventions of the law of 1891. _ "An adequate American ocean fleet would mean the sav- ing to this country of $100,000,000 which now goes to build up the commercial power and naval strength of Europe and Asia.' "The bill suggested wisely includes provisions intended to create and maintain a reserve of seamen for our naval ferces. There have been added to the navy. during the past year five large armored cruisers and there will be added during the coming year seven or eight first-class battleships and two armored cruisers and the resulting demand for increased enlisted force in the navy has brought keenly home to our naval officers the force of the maxim that 'No nation can maintain an efficient navy without a prosperous commercial marine to support it.' "During the past year evidence has accumulated that there is ample field for development and extension of the coast- wise steamship traffic and it is unquestionable that this can be promoted by the careful study of naval architects to the necessities of the trade if carried on simultaneously with the improvement in terminal facilities. The tendency will _no doubt be much enhanced by the encouraging efforts for the development of the marine turbine in the United States." SOME PROBLEMS.IN FERRY BOAT PROPULSION. Reading of papezs then became the order of the day. The first paper to be read was upon the subject "Some Problems in Ferry Boat Propulsion' by Col. E. A. Ste- vens, vice president. Col. Stevens has for several years made a specialty of ferry boats and his investigations are exceedingly interesting. The subject matter of the paper is well conveyed in his introduction as follows: "The propulsion of double-ended screw boats offers some difficult problems in screw design. The subdivision of the power shown by the indicator is very complex, and its exact distribution is, with the knowledge at hand, well nigh impossible. There are also few instances in which screw design is of more importance. The Scranton class of boats recently put into service on the Hoboken ferries can serve as an illustration. The wheel originally de- signed for these boats did not give satisfactory results in backing. It was decided to try a wheel of another type. The main dimensions were as follows: Wheel No. 1. ' Wheel No. 2. eee se ee te 16 6" eS 2° iii ste. 11' 144" 10 6" Bee Be eis eee 38.8sq. ft. 90.5 8d. ft: "The first wheel had blades of oval outline with rounded backs and a directrix curving to the rear. The second wheel was of the so-called DeLamater type, with sections designed to give equal efficiences in both motions and with vertical directrix. With greatly reduced slip the second wheel consumed about 20 percent more power at the de- signed speed without any appreciable gain in backing power. On the subsequent boats the original wheel was cut down in diameter and area." Power curves were submitted to show the results ob- tained by the Scranton with both wheels, and by the Scandinavia, a sister ship, with a smaller wheel of the same type. Col. Stevens then proceeded to discuss the results obtained to which attention will later be paid in the columns of the Review. DISCUSSION OF COL. STEVENS' PAPER. Prof. H. C. Sadler: Mr. President, there is one remark that I think Mr. Stevens might explain a little moze, and that is when he makes the statement that the thrust deduc- tion minus the weight gained in those boats is probably negligible in design. It seems to me that in an ordinary ferry boat with the bow propeller that the thrust deduction will remain much about the same as in an ordinary boat, -but the weight gained will be less. I should expect.that the hull efficiency in these boats would certainly not be ~ more than 95 percent, and probably less. I would like to know what Mr. Stevens thinks about that. This is, toa certain extent, I think, borne out by the efficiency curves. All the curves of total efficiency are very low for this type of boat. That is, the ratio of e to 1 never gets over 45 percent, if we omit the Edgewater. And there is no doubt there is some error in the Edgewater's curves, for it is practically impossible for this curve to run up in the way as shown. 'I should also like to ask Col. Stevens if he has performed any experiments or has noticed any tor-- sional vibrations in the shafts of these vessels. I think there is no doubt that there will be considerable to-sion vibration set up. Col. E. A. Stevens: The only method I know of in which the algebraical sum of thrust deduction and weight gained could be obtained is by single screw type; so that in those which have been attempted, as the Cincinnati, the Bergen and the Edgewater, the hull efficiency worked out at very close to 99, somewhere over 98. When you come to the double:screw condition it is practically impos- sible to separate the race augment from the total -sum. That efficiency falls to a very low figure; but I know of no process to obviate it. I have tried a number of times to get at some process by which the thrust deduction could be estimated apart from race augment, but I have been simply floored; I have been unable to get anything fur- ther. I suppose there is an increase in the screw motor for any design. The whole cannot be charged up to race augment, and no serious error will be involved, as the two losses are of kindred nature, and no difference really occurs, whether it occurs from the action of the bow screw or the stern screw.. As to torsional vibration, the shafts of these boats are usually much larger than would be .used in ordinary practice. I think that the very fact -- that they have been operating now for some time, very nearly 20 years,--some 18 years--practically without shaft troubles, shows that the shaft is working under very low stresses. I have not been able, except in one case, to suspect that vibration was arising from torsional vibration of the shaft. I havé never taken any such measurements as would give me any practical data on the subject, except the fact that I have never been able to trace the vibrations - to an unknown cause, which I would then call torsional vibration. : Mr. F. L. DuBosque: Col. Stevens has said. that it is impossible to analyze the performance of screw on ferry boats. It comes to us with a great deal.of satisfaction. We have been experimenting with these inclined wheels, as we call them, for the last 8 years, and we have been try- ing to analyze the forces to determine what size and type