[16] A detailed description of this valuable instrument will be found in [Appendix].
[17] Space forbids any detailed reference to these, but the names of the papers and their respective authors will be found enumerated in the list at end of chapter.
[18] An obvious means of dealing approximately with stability, to which limits of space will not permit more than simple reference, consists in so manipulating the data obtained by calculation for known ships that it may be made available, either in the form of curves or of tables, for determining the stability of proposed vessels. Methods of accomplishing this may of course vary to suit the ideas and convenience of designers. A well-arranged system was brought forward, jointly by Mr F. P. Purvis, head of Messrs W. Denny & Brothers’ scientific staff, and Mr B. Kindermann, one of his assistants, in a paper (see list at end of chapter) read before the Institution of Engineers and Shipbuilders in April last. While the results exhibited in the paper are immediately applicable to ships of one particular form, whatever the length, breadth, depth, or draught may be, this method still requires much development to make it at all universally applicable.
[19] It is the usual practice to assume vessels to be laden with homogeneous cargo of such a density as to fill the holds, and for this condition to estimate the position of centre of gravity to be used in calculation.
[20] See paper by Mr Kirk “On a Method of Analysing the Forms of Ships and Determining the Lengths and Angles of Entrance.”—Trans. Inst. N.A., vol. xii., 1880.
[21] With the view of effecting an economy in time, and to enable the trials at progressive speeds to be carried out while vessels are in a lengthened run out to sea, a method has been proposed by Mr J. H. Biles, naval architect to Messrs J. & G. Thomson, and adopted on board the vessels tried by that firm, and also experimented with on some of the vessels turned out by Messrs W. Denny & Bros., by which the necessity for running with and against the tide on the measured mile is entirely obviated. The principle of the method is to measure the time that a certain part of the length of the ship takes to pass an object thrown from the bows of the vessel well clear of the side. For full particulars, both of the apparatus employed and of the results of actual trials by this method compared with trials made on the measured mile, see paper on “Progressive Speed Trials,” by Mr Biles, in the Transactions: Institution of Naval Architects, vol. xxiii., 1882.
[22] A general outline of the operations conducted in Messrs Denny’s tank will be found in the description of their large works in [Chap. VI]. For a detailed account of the modus operandi in the same establishment, see abstract of a paper delivered in Dumbarton by Mr E. R. Mumford, of Messrs Denny’s Experimental Staff, printed in the Engineer for 15th February and the Steamship for 15th February of the present year.
[23] From experimental data obtained by Mr Froude, this correction can be made with certainty. The reasons for it may be explained as follows:—If an extremely thin short plane is drawn through the water it meets a certain resistance due entirely to surface-friction; that is, supposing the plane to be thin enough to eliminate wave-making and eddy-making. If the length of the plane is doubled while the depth is kept the same, the resistance at the same speed is not, as might at first appear to be the case, doubled accordingly. Owing to the friction of (say) the first half of the plane, the water is made to partake of the motion of the plane, so that the second half of the length, rubbing not against stationary water, but against water partially moving in its own direction, does not experience so much resistance from it. Adding a third equal length, it would have less surface friction than the second, and so on to infinity.
[24] See papers by Mr Mansel, enumerated in list at end of chapter.
[25] For description of apparatus, see Trans. Inst. Mechanical Engineers, 1877.