NOTES ON UFE-SAVING APPLIANCES. 



131 



for the pin davit, Table I giving the figures. The reason for this advan- 

 tage is that as the quadrant rolls out, the fulcrum also moves out, while the 

 working lever remains constant, the load lever being greatly reduced. 



Table I. 



Boat in inboard position, empty . . . 

 Boat in inboard position, loaded. . . 

 Boat in outboard position, empty. . 

 Boat in outboard position, loaded . 



Comparative effort on crank 17 inches long. 



Quadrant. 



lbs. 



232 



75 

 210 



Pin. 



lbs. 

 56J 



156 



lOI 



275 



Percentage. 



Quadrant 1 5 per ct. of pin. 



Quadrant 75 per ct. of pin. 



Thrust on screws. 



Boat going outboard, empty , 

 Boat going outboard, loaded 

 Boat going inboard, empty. . 

 Boat going inboard, loaded . . 



lbs. 

 415 



1,150 



3,650 



10,100 



lbs. 

 2,750 



7,600 



4,900 



13,700 



KormP=2><!2<^^l(^):, 

 K 



rA 



tan (0+6) =0.25 



c = o.90 



1" 



R=n" 



5 = thrust in screw. 

 P = power on crank. 

 a=screwpitch angle. 



6 = friction angle. 



c = friction in bearings and thrust. 

 y=pitch radius. 

 i? = crank radius. 



The thrust on the screws of the two types of davits is interesting, as 

 shown by the table referred to, and here again the quadrant type shows 

 advantageously, but, as before noted, the inboard swing shows less difference. 

 It must be remembered that the important thing to do is to swing the life- 

 boat outboard with ease, as when going outboard it would possibly mean a 

 very great saving of life by its more rapid handling ; but when boats are being 

 swung inboard, the necessity for speed or ease of handling is by no means as 

 important, as there would be less excitement and more time at disposal. 



Both types of davits referred to have the advantage of allowing the 

 overhang to be changed within the limits of the arms, and this advantage is 

 great as it lessens the danger of the boat swinging away from the ship's hull 

 and back against it. This danger, with a ship's deck 40 feet above the 

 water, is too apparent to be commented upon, but it is interesting to note 



