Note 23 — Chapter IV · PROGRESS IN THE SCIENCE OF SHIPBUILDING.

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.