200 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[September, 



from the interiiir ])art of tlie rectanj^le, so as to approximate to 

 the form of a diick's-foot, the rcsistani^e, wliether throiij^h air or 

 water, was the same — or, in other words, the resistance with llirrr 

 trUniyulnr or diirk-footed floats was as fjreat as j)revioiisly with 

 four rectaiif^iihir floats. Tliis apparent paradox \v^s, however, ac- 

 counted tor on the principle of the interior or detrimental jiortion 

 of the rectangular float being removed. 



Fig. 2. — Moditications of Ordinary System. 



A series of experiments on two other vessels was again made in 

 the years 18:?!), IHKI, and 1811, hy apjilyinf.;; different-shaped floats 

 to paddle-wheels of different diameters and widths, and on steam 

 vessels of different powers of from 6 to 90 horses; an abstract of 

 some of which was published in your Jmirmil for 1840. 



The fcdlowiiifi; were the particulars of the African when tried in 

 1837, previous to her being tried in 1841 : — 



ft. In. 



Length between perpendiculars 109 11 



Extreme breadth ... ... 24 10 



Mean draught 9 4.J 



Depth 10 



Nominal power of engines (by Maudslays and Field) 45 horses, 

 or 90 horses together. 



Number of strokes made by the engines per minute, 29 to 30. 



Barometer gauge, 24 to 26^ inches. 



Area of immersed miilship section, 1,50 square feet. 



Mean diameter of the paddle-wheels, 14"7. 



Area of the immersed rectangular floats, on thecydoidal or Gal- 

 loway system, twelve in number, 7 feet in length, and I ft. 9 in. 

 in breadth; thus presenting an .area of from .57 to 60 sq. ft., 

 being a ratio of 1 foot of float to 2--^ midship section. 



Fig. :i. 



Improved Trupezliim System. 



Fig. 4.— Improved Trapezium System, 

 With Wheels of smaller diameter and greater Velocity. 



When this trial was made in 1837, at the measured mile in Long 

 Roach, her average speed of six trials each way was 9-174 statute 

 miles ]ier hour with her rectangular flo.ats. Subsequently, she was 

 employed for towing and other ])uri)oses, and had never undergone 

 any other repairs than in her engines, and had never been in dry 

 dock : her bottom was consequently toul, and covered with green 

 weeds, when tried with the trapezium floats in 1811. 



Experiments on H.M. Stmnii-r '•African,' vitk Trapezium Floats. 

 First Trial, A/iri/ 14, 1841. 



All the rectangular floats, twelve in number on each wheel, were 

 removed, and twelve trapezium floats were fl.xed to the interior 

 and middle rings of each wheel: 



'J'hus making the area of the immersed floats, 34 square feet. 



Nunil)er of revolutions made by engines, 23j per minute. 



Mean speed of vessel in statute miles, U'l. 



Mean diameter of wheels, 17 feet. 



Fig. 5.- Improved'Trlangular System when the Vessel is Upright. 



Secoml Trial, April 'iX, 1841. 

 Number of revolutions made by engines per minute, 23. 

 Speed in statute miles per hour (weather very windy), 8|. 

 Third Trial. — Area of floutx reduced one foot each, and reefed-up 4 in. 

 Number of revolutions made by engines per minute, 25-3. 

 Speed of vessel in statute miles per hour 9-022. 



Fourth Trial, Jtine 8, 1841. 

 Number of revolutions made by engines per minute, 25. 

 Speed of vessel in miles per hour (weather windy), 8-8. 



Fig. 6.— Improved Triangular System when the Vessel is Inclined. 



Fifth Trial, June 9, 1841. — Ininiened float surface reduced to 29 sq. 



feet area, atid reefed-up 1 1 inches; or reducing the diameter of the 



wheel 22 inches. 



Number of revolutions made by engines per minute, 27j. 



Speed of vessel in statute miles ]ier hour 9-124. 



The barometer stood at from 25 to 26 inches. 

 Which result was nearly eipial to her former speed (viz. 9-174) in 

 1837, with rectangular floats of more than double the immersed 

 area of the trapezium floats. 



