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348 THe Marine Review a ee cae a Es bd ee * iS) fe S. S. Tacoma Maru in Dry Dock at BREMERTON, the master down and cabin boys, from passers entire crew, to the coal is Japanese. The Tacoma Maru is in every way -a credit to the rapidly growing mer- chant fleet that flies the red sun flag of Japan. TUG FOR PORT OF PORTLAND. The Port of Portland, Portland, Ore., thas advertised for bids for an additional steel bar-tug for Columbia river towing service. The new vessel will be built of steel according to approved specifica- tions and with tthe following principal dimensions: Length over all, 116 ft.; beam molded, 25 ft.; depth, molded, 15 -ft-- draugat,. aft;- 12: ft. 6 - in.; draught, forward, 10 ft. 3 in. The tug will tbe provided with a compound 'condensing engine, 20 in. and 44 in. in diameter by 28 in. stroke, two Scotch marine boilers, 10 ft. 6 in. in diameter by 11 ft. long and de- signed to carry a maximum pressure bf 170 tb. per. sq: in... Oil will 'be used for fuel. The new vessel was designed tby C., H. Norrlin, consulting engineer, Port- lang, Ore. PLANING PROPELLERS. The ordinary cast ipropeller, erther the solid type, usually far from being a true 'helix and the degree of variation differs at all points. True pitch propellers might ibe cor- rected 'by an amplification of the or- dinary screw cutting methods, 'but those of expanding or differential pitches cannot 'be so treated. however, except some extreme 'types such as the Hirsch, and whether the blades are raked or not, the surface lying along any radius is a straight line, and dt is thus possible to pro- duce a true helix 'by planing $0 long as the relative advance of tool and surface are correctly timed. As a geometrically correct surface is mani- festly more efficient than an imperfect surface,many attempts and devices have ibeen'made to produce it and the illustra- tions show a very successful adapta- tion at the works of the Fore River Shipbuilding Co., Quincy, Mass. In general arrangement of move- ments it does not, of course, differ much from others, but it is interest- ing as an example of adapting already of or sectional is In: all, WASH. existing equipment to special uses without destroying its usefulness for other punposes. A machine especially built for dealing with propellers up to large sizes would 'be extremely costly; in fact the annual charges on such a tool would probably pay for doing most of the planing actually required with the means here ent- ployed. Po tuis case a small planer is em- ployed merely to carry the tool and operate the feeds and the propeller is mounted on an entirely distinct and comparatively inexpensive 'base, the platen of which can be tilted as in Fig. 1 to correspond with ordinary take angles and carries a worm-oper- ated turn table on which the pro- ipeller is centered by the arbor shown. Fig. 2 shows the apparatus operating on a small propeller with little or no rake. The worm rotating operates with the table at any angle through the telescopic shaft and universal couplings as seen in Fig. 3. As the vertical feed of the tool and the ro- tary feed of the propeller must be simultaneous, 'both derived from gear are