64 Capt. McKonochie o^i the most effective use of' 



gravity of which may be kept low and immovable, may, under 

 all circumstances, ply them wider, and with the axle lower, than 

 any other description of steam-boat : this last circumstance being 

 also of importance, as shortening the lever by which the water 

 is displaced. 



5. It has just been observed, that steam-paddles ought not to 

 dip in the water above eighteen or twenty inches : — beyond this 

 point they are found rather to force it down and lave it up, 

 than press against it horizontally ; besides which, a disadvan- 

 tageous difference is made to exist between the velocity of the 

 upper and under edges of each paddle. Steam-boats, however, 

 plied on the usual principle on a ferry, must every trip plunge 

 them to a different depth according to their lading, and in par- 

 ticular, when they have a heavy cargo on board must sink them 

 greatly too deep for their most beneficial employment. They must 

 thus lose power precisely as they gain incumbrance, hghting the 

 candle, as it were, at both ends ; and the disadvantage of this 

 is now so distinctly recognized in steam-navigation, that the 

 most improved boats, some of the Irish packets for example, 

 have a contrivance for raising and lowering their paddles, accord- 

 ing to circumstances. The objection to this on a ferry, arises 

 chiefly from the trouble of the adjustment, and the little chance 

 there is, that in short trips and ordinary circumstances it would 

 be sufficiently attended to, although not merely the speed of the 

 boat, but also her wear and tear, will depend upon it. Steam- 

 tugs, however, which would never embark above a few foot- 

 passengers, and that only occasionally, would be exempt from 

 the inconvenience altogether. 



6. It has been ascertained by actual experiment in America, 

 *' that, to enable a vessel to stem a current with an absolute ve- 

 locity, equal to half the velocity of the current, it requires three 

 times the motive power, if that power acts on board the vessel, 

 that would be necessary, if the power were applied to a rope 

 hauling her." The details of the experiment are not given in 

 the work from which I quote (Papers on Naval Architecture, 

 edited by Messrs Morgan and Creuze, Naval Architects, Ports- 

 mouth Yard, vol. i. p. 309., Article, Analysis of Report made 

 to the French Government on the Steam Navigation of Ameri- 

 ca) ; and it evidently related to the different powers required to 



