212 LAUNCHING OF SHIPS IN RESTRICTED WATERS. 



She was launched at Copenhagen from the shipyard of Burmeister and Wain, under very 

 difficult conditions. It happened that there was heavy ice, 15 inches thick, in the harbor at 

 the time, and we had to cut a channel in the ice a thousand feet long to give the ship free 

 room for launching. We had considerable anxiety whether she would run too far or not. 

 On that occasion I felt the need of information of a reliable and scientific nature from which 

 to judge of how far the ship would run, but we had absolutely nothing, could not find any- 

 thing, and had to rely on our previous experience with rope stops. As far as this went, it 

 was very good, but this was the largest ship we had ever built in that yard, being more 

 than 5,000 tons displacement, and rather deep, so there was some anxiety connected with 

 it. However, it turned out all right. 



The next time I had to do with launching under difficult conditions was in the case 

 of the battleship New Jersey of the Fore River Shipyard. There was used on that occa- 

 sion the usual rope stops, but in addition there were two brakes, which were made up of a 

 long, wedge-shaped timber dragged longitudinally between two cross timbers, and the fric- 

 tion should absorb a certain amount of energy, but we did not get the full effect in that 

 case. The cross timbers broke, either because the wood was not of good quality or else 

 because the timbers were too light. 



In this paper is discussed a proposed new method of drawing wire rope through brakes 

 to give constant friction, and that seems to be a much more perfect method than the wooden 

 friction wedges, because the friction acts through a longer distance, so that a greater amount 

 of energy is absorbed. 



There is one point in the paper on page 304 which I think is of great interest, and that 

 is the comparison between the launching of the Kanawha and the Cuyama. The distance 

 run out by the Kanawha was only 329 feet, as against 444 feet in the case of the Cuyama, 

 although the Kanawha was considerably lighter, the difference being due to the stem mask 

 which was fitted. I believe that, of all the means of stopping a ship, there is nothing which 

 compares with the stern mask, because of the enormous hydraulic resistance it offers. 

 It is at once simple and effective. The faster the ship goes, the more effective is the mask, 

 which provides automatically for variations in the frictional resistance under the sliding 

 ways. 



I think the authors of the paper. Captain Gleason and Commander Saunders, are to be 

 congratulated on the application of model experiments in this connection and on the inge- 

 nuity which they have shown in working out the results and the interesting data they have 

 given us. They arrived, as I did when I had to do with the launching of the New Jersey, 

 at an analysis of the energy consumed. A study of the velocities and accelerations is, of 

 course, of interest, but that is not the kernel of the problem. The main point in an analy- 

 sis of launching and in designing for new launches is to know what happens to the energy. 

 There is a certain known amount of kinetic energy generated in launching. This energy 

 is reduced by frictional losses, which are also fairly calculable, but when the ship takes the 

 water it is difficult to estimate what becomes of the remaining energy. Evidently the greater 

 part is taken up in ordinary ship resistance, but we know very little about resistance under 

 these peculiar conditions, where the ship goes obliquely into the water, and any analysis of 

 that matter is, therefore, of the greatest interest. To the hydraulic resistance is to be added, 

 of course, the resistance of rope stops or other means of checking the ship. When we get 

 sufficient data of that kind, I think we will be able to launch ships with much greater con- 

 fidence. 



