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April, 1909 form the horizontal type of bossing is greatly inferior to the inclined type. Notwithstanding the fact that the lat- ter gives an increased wetted surface, between the limits of speed-length ratio of from 0.7 to 0.85 the increase in total resistance over that of the "naked" hull only varies from 3 to a little over 4 per cent, while for the horizontal type the corresponding in- crease is from 10 to 11 per cent. The effect of the two systems is, however, better seen by referring to Fig. 4. In this case the residuary re- sistance is shown for the two displace- ments, the corrected surface friction in each case having been deducted. Instead of ~actual residuary resist- ance, the resistance per "ton of displacement is plotted, and, in- stead of speed, the abscissae represent speed-length ratio, or speed in knots divided by the square root of the length in feet. Mention is made of this method of plotting be- cause the curves so obtained are in- dependent of size or density of wat- THe MarRINE REvIEw er, and will apply to any ship of which the model is a type. This has been adopted as the standard method of plotting residuary resistance both at the University of Michigan and at the United States government. tank at Washington, and is the simplest form for direct application to practical problems. Within the limit of speed-length ra- tios before mentioned, the inclined sys- tem of bossing for the two displace- ments increases the residuary resist- ance by a very small amount, which at some speeds is negligible, while in the horizontal type the increase aver- ages from between 30 and 35 per cent. Comparing the curve of residuary resistance .for No. 2, or the. inclined bossing with that of the "naked" hull, it is obvious that the stream-line flow cannot have been materially changed in the two cases. This conclusion, to a -certain -extént, bears: out. -Laviors stream-lines, and if the buttock-lines of No. 1 be compared with those of No. 2 and also with the "naked" hull Fig.1. NOT. HORIZONTAL. 'TYPES OF BOSSING. the result is, perhaps, only what might have been expected. The above experiments give, how- ever, quantitative results for purposes of comparison, and emphasize the: im- portance of attention to such details as designs. Attention may also be called to the fact that a number of fast Atlantic liners have been fitted with horizon- tal bossing. FOUR BLADES FOR LUSITANIA. The Cunard liner Lusitania is soon to be dry docked at Liverpool, where she will be fitted with four-bladed propellers instead of the three-bladed ones with This will be done with a view to increasing her which she is: now equipped. speed as the results obtained by a like: change on her sister ship Mauretania were very satisfactory and she has since been breaking all records on her trans- Atlantic trips. . Bad NOW. 45 QECREES. Residuary Resistance. Lbs. per Ton Displacement. ( ~