[45] IT. S. FISH COMMISSION STEAMER ALBATROSS. 47 



Diameter of the outboard end of the small gypsy heads iuches.. 11 J 



Diameter of the middle of the small gypsy heads do 8$ 



Length of the small gypsy heads on line of their axes do 12$ 



Total length over the three gypsy heads do 113$ 



Diameter of the main shaft do 4$ 



Diameter of the spur wheel at the pitch line do 40 



Pitch of the teeth of the gearing do 2-jV 



Width of the face of the gearing do 6 



Width of the face of the friction brake do 4 



Number of journals on the main shaft 2 



Diameter of the journals on the main shaft inches.. 4 



Length of the journals on the main shaft do 13 



Diameter of the pinion on the pitch line do 9 



Number of steam cylinders 2 



Diameter of the steam cylinders inches.. 10$ 



Width of the piston trunks fore and aft do 9 



Width of the piston trunks athwartship do 2f 



Area of cross-section of each trunk square inches.. 23$ 



Net area of the steam pistons, each do 74.K4 



Stroke of the pistons inches.. 10 



Number of journals on the crank shaft 2 



Diameter of the crank-shaft journals inches.. 3J 



Length of the crank-shaft journals do 6 



Diameter of the crank pins do If 



Length of the crank pins do 2 



Length of the engine base fore and aft do 60 



Width of the engine base athwartship do 96 



Height of the engine do 53$ 



Weight of the engine pounds.. 6,500 



POWER OF THE DREDGING- ENGINE. 



The wire rope from the dredge passes over the dredging block at the 

 end of the dredging boom, then under a sheave in the heel of the boom, 

 then upward and over a block suspended from the " accumulator." and 

 then to the central (or large) gypsy head of the dredging engine. 



The "accumulator" (Plate XLIY), which is a series of rubber 

 "buffers" moving freely on their longitudinal axes by the tension on 

 the dredge rope, becomes a good dynamometer, though its motion is 

 small and its scale fine. By taking a large number of dynamometer 

 readings simultaneously with indicator diagrams from the dredging 

 engines, noting at the same time the actual velocity of the rope as it is 

 measured by the register on the boom sheave and also the speed of the 

 engines, and by taking the mean of these quantities we shall approach 

 very closely to the true conditions. 



The gypsy head, by which the wire rope is wound, is curved, and the 

 rope comes in, consequently, on a varying diameter; as the mean ^ 

 velocity of the wire is less than that due to velocity of the center line 

 of the wire wrapped on the smallest diameter of the head it is evident 

 there is a slip. The tendency of the rope, winding on the head, is to coil 

 into a helix, but the inclination of the surface causes the wire to surge 



