I40 NOTES ON LIFE-SAVING APPLIANCES. 



doubtful whether this will be found to be the case in practice, and it is probable 

 that on account of the various frictional resistances mentioned above, the quadrant 

 type will be found considerably harder to rig in than a properly designed screw- 

 operated fixed-pin type. 



It is not explained in the paper that the pin-type davit mentioned on page 132 

 as being tested with very unsatisfactory results is an entirely unusual arrangement, 

 wherein both davits are operated together through the meditation of a steel shaft 

 connecting the two, this shaft being revolved by means of a worm quadrant, worm 

 and spur gears, ending in a hand crank operating the entire arrangement. This 

 apparatus resembles a quadrant davit about as much as it does the usual pin-type 

 as previously discussed in the paper, and it is very misleading to mention this as 

 "The very interesting, practical and convincing test, which showed the disadvan- 

 tage of the pin-type davit," without explaining more in detail exactly what kind 

 of a pin- type davit it is; but of course this feature probably did not occur to the 

 author of the paper, as he doubtless intended no misrepresentation. The perform- 

 ance of the quadrant davit mentioned on the same page is about the same as should 

 be expected of a well-designed screw-operated davit of the fixed-pin type, and is 

 about what has been accompUshed with the sheath-screw davit. 



The principal advantage of the sheath-screw davit is that in stowage position 

 the screw is completely housed and protected by the sheath and the sheath may be 

 filled with grease for lubricating the screw. 



In the quadrant type illustrated in the paper, the screw and guide shaft are 

 exposed to the weather, protected only by a flat cover-strap an inch or so above 

 the guide shaft, and although they are both of brass, it would seem that the action 

 of air and sea-water must considerably increase the friction unless they are kept 

 carefully cleaned and frequently greased. It also seems that a careless man might 

 put a coat of paint on the guide shaft, the average painter being likely to consider 

 it as proper a thing to paint as the cover-strap just above it. The quadrant, rolling 

 in the groove with its gear teeth meshing with those in the deck rack, seems also 

 to give such good opportunity for the accidental presence of foreign substances 

 to make trouble, that it is remarkable trouble does not more often occur. Undue 

 roughness or irregularity of either quadrant or deck casting will produce wedging 

 action between the deck casting and guide shaft, or else throw all the weight of 

 both boat and davit on the guide shaft. However, the large number of quadrant 

 davits in successful operation shows that these conditions adjust themselves through 

 the spring of the material, or in some such way, but it appears possible that they 

 may make one davit of this type less easy to operate than another, and the same 

 davit more or less easy to operated at different times, depending upon the kind of 

 care it has had. 



The sheath-screw davit is an attempt at still further simplicity and fool- 

 proofness, by further obviating the necessity for care. But there is still something 

 to be desired, as the pivoted thrust bearing on the deck frame is now exposed to 



