STEAM NAVIGATION. 



British, navy. An end view or an elevation looking against the end of the 

 shaft is shown in fig. 18. Smith's three-thread screw differs from this 

 only in having three arms instead of two. 



Fig. 21. 



Fig. 23. 



Strimman's propeller is shown by an end view in fig. 19, and a side 

 view in fig. 20. 



Sunderland's propeller, as applied in the "Rattler," is shown in fig. 21, 

 consisting of two flat plates, set upon arms, fixed to an axis revolving 

 beneath the water in the stern. In the "Rattler," this propeller was placed 

 in the stern in the dead wood, instead of projecting out behind the rudder 

 as in the Sunderland arrangement. 



In fig. 22 is represented Woodcroft's propeller, also applied in the 

 "Rattler." This has four arms or blades, and the pitch of the screw at its 

 leading edge is less than the pitch at its terminal edge. 



In fig. 23 * is represented, as set in the stern of the vessel, the form 

 of Hodson's screw, from which excellent results are said to have been 

 obtained. This form of screw has been much used in France, Holland, 

 and other countries of the continent ; and in some cases in which the com- 

 mon screw has been superseded by a screw of this description, an 

 improvement has been obtained in the speed amounting to about a knot 

 an hour. Such results will only ensue when the original screw has been 

 of inadequate dimension, so that the loss by slip has been large in amount, 

 and the more the slip is reduced, the less will become the advantage of 

 any deviation from Smith's form of screw with uniform pitch.f 



* Figs. 17 to 23 have been taken with the permission of the author 

 from Mr. Bourne's work "on the Screw-propeller." 

 t Bourne " on the Screw-propeller," p. 136. 



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