Cutter yacht 'Britannia'—general arrangement plan.
Prior to 1870 but little was known of the laws governing the resistance to bodies moving through water. It is true that eighty years before this, towards the close of last century, Colonel Beaufoy had made an elaborate series of experiments in towing bodies through water, beginning first in one of the tanks of his father's brewhouse. These were elaborated in the Greenland Dock near London, and included the determination of the resistance of all manner of shapes, except unhappily shipshape ones, the nearest approach to these being double wedges, and double wedges with a straight amidship piece inserted. But while Colonel Beaufoy also made experiments for the determination of the value of surface friction on planes pulled through the water, no great importance seems to have been attached to these by shipbuilders in general, and the subject of surface friction was more or less lost sight of by them until again brought forward by Maquorn Rankine, first in a series of papers in the 'Mechanic's Magazine,' and more elaborately in his 'Shipbuilding, Theoretical and Practical,' published in 1866. In this Rankine, basing his deductions on Weisbach's experiments on the flow of water through pipes, concluded on mathematical principles that the entire resistance at moderate speeds of a fair and easy formed vessel was due to surface friction—i.e. the rubbing of the water against the sides and bottom of the ship. Rankine showed also that at higher speeds the forming of waves was a material and ever-increasing element in the resistance.
It is fully twenty years ago that the late Mr. William Froude began to give to the world the results of his experiments on the resistance of planes of different lengths, coated with various substances and towed at varying speeds through the water. These experiments were conducted under the most favourable conditions, and with the nicest regard for accuracy, and practically confirmed Maquorn Rankine's deductions, although it was found that Rankine had somewhat overestimated the value attachable to surface friction, and had also overestimated the increase in frictional resistance, due to increased speed. Still the great fact remained that practically the entire resistance to a fairly formed body, moving through water at moderate speeds, is due to friction and to friction alone.
Rankine's reasoning, early in the sixties, had been too subtle for those fathers of shipbuilding at that date engaged in the art. Able, honest, practical men, most of them could have handled an adze, or maul, with the best of their workmen, and were more at home fairing a sheering batten, or directing a launch, than in analysing speed curves, or investigating strength calculations.
But one or two of the younger and brighter minds in the profession, more especially those who had the advantage of Rankine's direct tuition, felt that the old beliefs as to resistance presented such anomalous and unreconcilable results that they could not be founded on any true law of nature. John Inglis, jun., then a mere boy, instituted in Pointhouse Shipyard Rankine's method of estimating the resistance of ships, and for many years was alone in this mode of investigation.
Resistance curves
Model of S.S. 'Merkara.'