24 REPORT — 1869. 



bluff-bowed boat was towed across the dock by a rope and winch, worked 

 by labourers, the rope being fast to a spring weighing-machine on board the 

 boat. The boats tried were of somewhat bluff form, and it was found that 

 the resistance varied only roughly as the velocity squared, increasing faster 

 than that at high speeds. The drawings of the boats are not given with all 

 the detail that could be desired, nor is the condition of their surface minutely 

 described ; but the experiment was in the right direction, being upon 

 actual boats meant for use, and of a size far exceeding the models of pre- 

 vious experimenters. 



Some experiments by Mr. Colthurst, both on the forms of floating bodies 

 as affecting their resistance to motion, and on the friction of wetted sur- 

 faces, are given at p. 339 of vol. xxiii. of the ' Civil Engineers' Trans- 

 actions.' 



We also refer to the Eeport of the Committee appointed by the British 

 Association upon the comparative resistance of bodies wholly and partially 

 immersed (B. A. Reports, vol. for 1866, p. 148). The Committee decided to 

 print the observed facts without any deductions. It is not necessary to the 

 purposes of this Report that we should discuss them. We have already 

 alluded to the difficulty which they indicate as being felt with respect to 

 the way in which the water of replacement flows in at the stern. 



We wHl next refer to the experiments of Captain Bourgois, which were 

 begun at Indret, in 1844. He first had several boats from 22 to 2-5 feet 

 long towed by the 'Pelican' steamer, then under his orders, and later a 

 small merchant schooner of a little over 60 feet long, and afterguards the 

 ' Fabert,' a brig 98 feet long. These vessels were simply towed, and their 

 actual resistances measured with a traction-dynamometer. Similar experi- 

 ments have also been tried in France with the screw-steamer ' Sphinx,' 109 

 feet long ; with the screw despatch-boat ' Marceau,' 131 feet long (with its 

 screw upon deck), and with the 74-gun ship ' Duperre,' 180 feet long, buUt 

 by Sane. Probably nothing could be better than the experiments thus made, 

 and it is from these that M. Bourgois has derived the coefficients of the 

 formulte which he has given. But, unfortunately, the particulars of the 

 ships experimented upon are not given in great detail, nor are theii" draw- 

 ings published. The only particulars given are the length and breadth on 

 the water-line, the di'aught, and the area of midship-section immersed, but 

 without wet surface, or even displacement. 



M. Bourgois's memoir has no date ; but it is evidently later than 1853, 

 since he mentions that as the date of the experiment. It also contains some 

 results of trials of propoilers set to work against a dynamometer with the 

 vessel made fast, and some trials depending upon the measurement of the 

 power exerted by the engine. But we do not proj^ose to discuss the trials on 

 steam-ship performance. Not only is this the work of another Committee, 

 but, inasmuch as they introduce the uncertain effects of the engine and 

 propeller, they fail to give any accurate account of the resistance of the 

 water. 



In the earlier history of the subject, it was supposed that models would 

 most aptly represent ships at the same speed both for the ship and the 

 model. The exi^eriments at the East-India Import Dock in 1827 and 1828 

 seem to show a dissatisfaction with the results of small models ; and some time 

 later, M. Rcech, the Director of the Ecole d' Application du Genie Maritime 

 in France, pointed out that models of different sizes intended for comparison 

 should be made to move at velocities varying as the square roots of their 

 lineal dimensions. In this case the actual resistances would vary as the 



