The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

"". vance ee / illustration No. 3, in place below the truck; at the bow and stern are guides to prevent it "zawing," but not in any way to pull or retard it. The opezator holds the model by means of two ver- tical levers until the truck has attained a uniform speed, when he allows the model to pull on the dynamometer, letting it go gradually. On one side of the tank, from north to sotth, are "mile-posts" -- small contact-makers alongside the rail 25 ft. apart. On the resistance drum the follow- ing are recorded: (1) The resistance in pounds; (2) the distance traversed in multiples of 25 ft.; (3) time in half seconds; (4) a measure of the current | in the water as recorded by the revolu- tions of two log-screws running in ad- of the model; (5) a graphic measure of speed from a strophometer, used for detecting any want of uni- formity of motion, this is geared di- rectly off the driving shaft. Nos. 2, 3 and 4 are recorded by pins actuated by electro-magnets. From Nos. 2 and 3 speed in feet per minute "over the land" is obtained, and, when corrected "for current, speed through the water is got. Then for a given model at known draughts and of known. displacements, 'the resistance in pounds and speeds in feet per minute are obtained. _ In special cases the trim is measured while on the run, by graphically re- cording the change of level at the bow 'aud: stern. Then a. -vertical: rod~ of -aluminum is supported on a knife-edge on the boat, and carries a pin at its upper extremity. This pin marks pa- per on a vertical cylinder, on which is traced a datum line; as the model is run down the tank, this cylinder re- volves, and the pin marks the rise or fall of the bow or stern with -regard to this datum line. Alterations of trim and draught when running are of great importance in paddle steamers,-as are also wave configurations along the ves- sel's side; these latter can be accur- ately got from the model experiments by photography, and the proper paddle float immersion given. On the screw-truck time, distance and revolutions of the screw-propell- ers are recorded on the rotating drum ~ by the aid of electro-magnets with pen atms attached. "fhrust" .and "belt" in pounds are weighed by means of spiral springs, and automatically re- corded. . Many refinements are intro- duced to redute friction such as ball- bearings, etc., and the masses of the gurnard and shafting are balanced by weights about the upper watch springs. 'Idle "thrust" and "belt," i. e., with the propellers off, are recorded under the same conditions as gross "thrust" and "belt,* and the net value of these due THE MARINE REVIEW _ to the presence of the propellers. ascer- tained. Friction due to the load of the propellers can also be allowed for. By the aid of this part of the appara- tus such problems can be solved as "propeller efficiencies," associated with definite "thrusts," while, in conjunction with the main truck, the following can be ascertained: "Wake factors," "thrust deductions," and "hull efficien- cies." One corner of the tank building is devoted to the making of propellers 'and one illustration, No.,5, shows a 'number of propellers that have been used experimentally. A light lathe also shown is found very useful in "tipping up," boring and finishing the bosses of propellers, and in the general work of the department. The results of all model experiments are first plotted in curves of resistance in pounds on a -base of speed in feet per minute. Af- terwards they are reduced to the con- stant system introduced by Dr. R. E. Fronde. Tank experiments can only supply values of effective horsepower for given forms; to get the correspond- ing I. H. P., a propulsive coefficient has to be used. This is purely a matter of judgment, based on previous experience with similar ships and _ engines, al- though the introduction of turbines -renders a knowledge of the effective horsepower more desirable than the indicated horsepower as used in reciprocating engines. Still it cannot be too strongly enforced that pro- gressive speed trials should be con- ducted with the greatest care, and the results critically analyzed. Otherwise propulsive coefficients cannot be accur- ately obtained, especially as the range they may cover is considerable. The makers of this experimental tank are Messrs. Kelso & Co., electricians and model makers, Glasgow. In this connection Messrs. Kelso & -Co. have just received an order for all the apparatus for an experimental tank, which is'to be constructed at the works of a leading Japanese' ship building firm. The name of the firm has not yet been officially divulged, ° but it is almost certain to be the Mitsu Co., of Nagasaki. This is the princi- pal ship building firm'in Japan, and during recent years extensive improve- ments have been made at their works. The new tank for the Japanese is to be practically a duplicate of that re- cently constructed: in the. yard. of Messrs. John Brown & Co., Clydebank. It will have a water way about 445 ft. in length, of which 4oo ft. is deep vary- ing. from 9 ft. at one end to Io ft. at the other. The breadth will be uni- formly about 20 ft. and it will be pro- vided similarily with small wet and dry docks, and all the necessaries detailed : in that at Clydebank. The making of © the actual tank and the building cov- ering it will be done by Japanese con- tractors, but otherwise everything will be supplied by Messrs. Kelso, their contract including not only the carri- age and recording apparatus, but also the dynamos and the model cuttifg machinery, and even the rails on each side of the tank, on which the carriage supporting the apparatus will run. The intention of the firm is that everything shall be in working order and capable of being tested in Messrs. Kelso's shop before being sent to Japan. Like the Clydebank tank that in Japan will have apparatus worked by electricity. MEASURING A VESSEL'S TON- NAGE. Eugene Tyler Chamberlain, commis- sioner of navigation, Washington, D. C., has recently rendered an opinion to the surveyor of customs, Memphis, Tenn., which is of interest to' vessel owners generally. The opinion is rendered in the case of the sternwheel river steamer Dardonelle. This steam- er has a freight "space, boiler space and engine room on the main deck. The spaces are open at the side and forward and are roofed over or cov- 'ered by a canopy or shade deck, sup- ported by stanchions not having a di- rect bearing upon the frames. The spaces are open to the sea and weather and the deck above them-. is apparently. = not --a.- deck. -to°> the hull within the meaning of the custom regulations of 1899. The engine room is enclosed. The ques- tion whether the freight space should be measured for' inclusion in such a vessel's tonnage has been submitted to various. collectors located on the Mississippi river and its tributaries, the great lakes and the coast. - Dis- similar opinions have been expressed, 'the majority of collectors holding, however, that the spaces are exempt from measurement. Among these are the custom officers at principal ports, including New York, " Philadelphia, Cleveland and St. Louis. - Commission- er Chamberlain decided that the spaces in question should not be measured or included in the vessel's' tonnage. Were the sides boarded up or enclosed so as to protect the freight carried from the sea and water the freight space would be measurable, although it might be open at the forward end. Joseph R. Oldham, superintending and consulting engineer, well known on the great lakes, announces that he has opened an office at No. 1005 Mon- adnock building, Chicago, Ill.