586 THE PROGRESS IN STEAM NAVIGATION. 



ing power devel()i)e(l with e(iiijil cffifioiicv, the loss of speed would 

 approximate to 4 knots. These ilhist rations only eontirm oenerg,! 

 experience that clean bottoms are essential to economical propulsion 

 and the maintenance of speed, and tluit frecpient dockinji" is necessar}' 

 in vessels with bare iron or steel skins, which foul in a comparatively 

 short time, 



POSSIBILITIES OF FURTHER INCREASE IN SPEED. 



From the facts above mentioned it is olivious that the increase in 

 speed which has l)een effected is the result of many improvenuMits. and 

 has been accompanied l)y larjife additions to size. en»iine ])()wer. and 

 cost. These facts do not discoui'aii-e tiie inventor, who tinds a favorite 

 tit'ld of operation in schemes foi- attaining- sp(»eds of 50 to HO knots at 

 sea in vessels of nioch'rate size. Sometimes the key to this remai'kable 

 advance is found in (levic(>s for reducing' snrfa<'e friction by the use of 

 wonderful iuliricants to he ajjplied to the wette(l surfaces of shi])s, or 

 b}' interposinji' a layer of air l>«»tween the skins of ships and the sur- 

 roundinji' water, or other departures from ordinary practice. If these 

 H'entlemen woidd " condescend to Hg'ui'es.'" their estimates or guesses 

 wouhl l>e less sanj^uine. in many cases the projiosals made would fail 

 to produce any siMisible reductit)n in resistance; in others it would 

 increase resistance. Other proposals rest upon the idea that resistance 

 ma}^ be largely reduced hy adopting novel forms, departing widely 

 from ordinary ship shapes. N'ery often small-scale experiment?, made 

 in an unscientitic and inaccurate manner, are adduced as proofs of the 

 advantiiges claimed. In other instances mere assertion is thought suf- 

 ticient. Ordinarily no regard is had to other considerations, such as 

 internal capacity, structural weight and strength, stability, and sea 

 worthiness. Most of these proposals do not merit serious considera- 

 tion. Any which seem worth investigation can l)e dealt with simpl}' 

 and effectivtiy by the method of model experiments. A striking 

 example of this method will be found in the usual form of a parlia- 

 mentary paper — -No. 318, of 1878 — containing a report made by Mr. 

 AVilliam Froude to the Admiralty. Those interested in the subject 

 will tind therein much matter of special interest in connection with the 

 conditions attending abnormally high speeds. It must suffice now to 

 say that ship-shaped forms are not likely to be superseded at present. 



The most prolific inventions are those connected with supposed 

 improvements in propellers. One constantly meets with schemes 

 guaranteed b}' the proposers to give largely increased efficiency and 

 corresponding additions to speed. Variations in the numbers and 

 forms of screws or paddles, the use of jets of water or air expelled 

 by special apparatus through suitable openings, the employment of 

 explosives, imitations of the fins of fishes, and numberless other depart- 

 ures from established practice are constantly being proposed. As a 



