220 



Art. LIV. — On the Comparative Performances of certain River Steamers, on 

 the Waikato. By James Stewart, C.E., Inspector of Steamers, etc. 



[Read before the Auckland Institute, September 20, 1869.] 



During an official visit to the Waikato, a few months ago, I was enabled to 

 collect pretty definite particulars of the comparative performances of side 

 paddles and stern wheel, as applied to the steamers " Blue Nose " and 

 "Rangiriri." Two vessels differing widely in construction, and, as the 

 investigation proves, just as much in effective results of the applied steam 

 power. I have worked the comparison in various points, and now take this 

 opportunity of laying the same before the Institute, feeling assured that it will 

 prove of interest to many. 



The construction of these vessels is known to all who have been interested 

 in the Waikato during the last five years. The " Blue Nose " is a wooden 

 vessel, propelled by side paddles of the common sort. The " Rangiriri " is an 

 iron vessel, with a single feathering paddle wheel at the stern. The " Blue 

 Nose " is moderately fine in shape, while the other is hideously bluff at the 

 bows, straight in the sides, and square in the stern. Both vessels have direct- 

 acting, high-pressure machinery, and nearly the same draft of water, but with, 

 these similarities their points in common cease, and a wide divergence on 

 all others takes place, the particulars of which are the subject of this 

 paper. 



In comparing the vessels, it will place the matter more clearly, if the 

 various points are tabulated as under. 



POINT OF COMPARISON. 



Ratio of beam to length . 

 Immersed midship section 

 Cylinders 



Steam pressure during trial 

 Revolutions per minute . 

 Computed indicated h. p. 

 Speed per hour 

 Paddles 



Effective diameter of wheel 

 Slip of wheels 

 Ratio of immersed floats to 

 immersed midship section 1:1-9 1 : 2 - 4 



It will thus be seen that, notwitstanding the very great advantages 

 in point of build, power, etc., the " Blue Nose " only attained a very 

 small increase of speed over the " Rangiriri." To put the comparison 

 more clearly on this point, let the usual Admiralty formula be taken to fix the 

 value of the constant of efficiency, premising that for vessels of similar build, the 

 larger the constant, the greater is the useful effect of the power applied. This 



rule is C = =5—^ in which C is the constant, and "V the speed in knots per hour ; 



S the area of immersed midship section, and HP the indicated horse power. 

 Reducing from the above values of those signs, we find for the " Blue Nose " 

 C = 207, and for the " Rangiriri " C = 377. The result is sufficiently startling, 

 and in great part must be accounted for by the faults of the " Blue Nose," 

 although I have been aware, ever since the " Rangiriri " was placed on the 

 river, that the stern wheel developed more useful effect than the side wheels. 

 But I never had an opportunity, until lately, of fully comparing them. 



Before attempting to give a reason for the above result, I will mention 



"blue nose." 



"RANGIRIRI." 



1 : 6-3 



1 : 4 



40 sq. ft. 



55 sq. ft. 



13^ in. x2ft. 4 in. 



11| in. x 2 ft. 3 in. 



56 lbs. per sq. in. 



51 lbs. 



28 



25 



53 



31-5 



6 - 5 knots 



6 knots 



Common 



Feathering 



10-7 ft. 



9-2 ft. 



30 per cent. 



17 per cent. 



