I30 NOTES ON LIFE-SAVING APPLIANCES. 



cumstances this is of great assistance, dispensing of course with the guying, 

 but then comes the control. The round-bar davit has but one reach or 

 overhang, and this is a serious disadvantage, but in this form it cannot be 

 obviated, so beyond strength the round-bar davit does not meet the require- 

 ments of the high sea. 



There have been several forms of self-acting davits presented, that is, 

 they are so designed as to require only a small applied force to send them 

 outboard. Those I have seen worked well enough in smooth water yet they, 

 again, were either all inboard or all outboard and were hampered by too much 

 mechanism into which ice, lines or other obstructions could easily get. 

 Much ingenuity has been shown in this style of davit but none that I have 

 seen seemed to fill any of the three requirements I have named, not even 

 strength. 



What may be called the fixed pin type of davit has been presented over 

 and over again to the marine world. Plate 60 shows one of these. Here the 

 form was used to meet conditions where deck room was very limited; this 

 form has the advantage of being cheap. The screw which actuates the 

 swinging arm is sometimes placed in a sleeve to protect it. The overhang 

 of this davit is under control, which is one of the conditions I have named, 

 but it is strong only in one direction, viz., across ship ; but if a ship was pitch- 

 ing even moderately, should the lifeboat in swinging out strike the screw, 

 great damage would result and most likely render the davit useless. The 

 breadth of hinge, as it may be called, is relied on to give fore-and-aft strength, 

 but it is evidently weak in this respect; unless made very much greater in 

 in length than is shown in the figure, the construction would be far from 

 rugged. 



The fixed pin form just commented upon has for its counterpart the 

 movable pin style, which is shown in Plate 61 . Here a segment of a circle car- 

 ries the arm and a screw controls its movement across ship. The advantage 

 of this form of davit is most clearly shown by Table I and accompanying 

 diagram; here the eff'orts on the screw are to be seen, as well as the effort 

 required on a crank for swinging inboard and outboard. The weight of boat 

 is taken as 3,500 pounds. In the pin davit 58 pounds' effort on the crank is 

 required to swing the boat, while in the quadrant type but 8^ pounds are 

 needed; this is with an empty boat. When loaded (an additional weight of 

 7,500 pounds), the pin davit takes 160 pounds' effort as against 23I pounds' 

 effort for the quadrant type. This figures out that the quadrant davit takes 

 but 15 per cent of the power of the pin type, certainly an advantage. In 

 swinging inboard, however, the advantage of the quadrant type is not so 

 great as is shown by the table, since it takes 75 per cent of the effort required 



