134 STABILITY OF LIFEBOATS. 



Number 3 was of radically different form and falls within the class commonly 

 called decked lifeboats, as the passengers are carried above a second watertight 

 skin or deck. It was built of metal (No. 14 B. W. G. galvanized iron) in accord- 

 ance with the construction plans on Plate yy. The lower space, with its water- 

 tight subdivision, serves at all times as an hermetically sealed buoyant chamber. 



Number 4 is called a collapsible boat and consists essentially of a flat pontoon 

 of wooden construction pointed at each end, and provided, with wooden thwarts, 

 rail and canvas bulwarks. These all fold down on to the upper deck or can quickly 

 be raised and clamped into position when the boat is to be used. A construction plan 

 in detail was not available for this type, but its general characteristics are shown by 

 the figure on Plate 76. Compactness of stowage and the suitability for nesting have 

 been factors which have influenced appreciably the design of this type. 



All boats were new, in the best of condition, and had been obtained direct 

 from the makers. 



In order to be of the most value a basis for comparison must be used which in- 

 volves either size or capacity. The former was chosen, and all boats were of the 

 28-foot size. 



The inclining experiments were carried out using two plumb-bobs (one at each 

 end) about 5 feet long. Pig lead was used for the inclining weights, and readings 

 were taken with the lead on the center line amidships, then to port, starboard and 

 back to the center line. The boats were in all cases in absolutely quiet water, and 

 several readings were taken for each position with an agreement which was en- 

 tirely satisfactory (seldom over one per cent). 



The worst case as far as stability is concerned is when the boats are loaded 

 to their full complement, and that condition was simulated by loading the thwarts 

 with sand bags (about 75 pounds each) so stowed that the center of gravity of 

 each pair of sacks was at the proper height for a man sitting in that place. The 

 height that this should be was determined by balancing a man fast to a plank in a 

 sitting position and was found to be very close to 9 inches above the seat. Al- 

 though two sacks averaged close to 150 pounds, the ballast was weighed each time 

 it was put aboard in order to check the total weight. In most cases there were 

 several persons in excess of the allowed load on board when investigating for the 

 full load condition; but the resultant curves of stability, both statical and 

 dynamical, have been corrected so they include only the number of persons that 

 the inspection rules permit. 



The derivation of the moments and areas of the sections for the many incli- 

 nations has been with the aid of mechanical integrators and the results have been 

 plotted as curves. These curves have in turn been integrated to obtain the final mo- 

 ments and volumes. This was done because where the boat has quick changes 

 of transverse form or when the rail goes under the area and moment curves are 

 abruptly irregular and any numerical summation is apt to be seriously in error. 

 A complete set of the curves for one of the larger angles of inclination is shown 

 on Plate 79 to illustrate the method of arriving at the resultant curves of statical 



