SECT . x .] OF STEAM NAVIGATION. 319 



The average consumption of coals is that required when the engine is in full 

 action, and including all delays, waste, &c. ; and is to be understood as that which 

 multiplied by the hours it requires for the average passage, would give the quantity 

 consumed for each passage ; and the store ought evidently to be for the longest 

 passage. In the best engines (of this time) it will be found to vary from 12 to 16 

 Ibs. of Newcastle coals per hour for each nominal horse power, and in inferior 

 engines it may extend to 20 Ibs. 



When the consumption is stated at less than it amounts to, at 12 Ibs. per hour 

 for each nominal horse power, it may be fairly esteemed an experimental trial ; and 

 of course the fires are more carefully attended, with every precaution to prevent 

 waste and give effect. The last column of Table HI. will nearly give the fuel 

 required per hour if the nominal power be taken in the first column, (art. 664.) 

 when applied to steam boats. 



The velocity of sea vessels appears to average about ten miles per hour ; their 

 power to face a wind is inconsiderable, because the wind gives the surface of the 

 water so much velocity, that the paddles act with less force in proportion as the 

 velocity of the water approaches to the difference between the velocity of the 

 paddles and that of the vessel ; and when these are equal, the boat will commence 

 moving backward ; and it is also with much reason supposed that the action of the 

 wind itself tends greatly to retard a vessel's motion when it is directly opposed to 

 it : for if a vessel of 100 horse power has a surface of 60 yards above water, 1 and 

 the velocity of the wind be 50 feet per second, (in which vessels are under their 

 courses,) then by the equation, (art. 647, note) 



2500 x 60 ,- i 

 "3200 = 47 horse power, 



for the resistance offered to motion when the vessel is at rest; and as with 

 whatever velocity the vessel moves against the wind, this velocity should be added 

 to that of the wind, the plus sign being the proper one, in the equation for this 

 case it will appear that the power to move forward is extremely limited with so 

 much surface above water. 



The only vessels in the table, art. 657. which have dimensions to enable us to 

 approximate to their speed, are the 'Lightning' and the 'Dee;' and, notwith- 

 standing the great quantity of power to be placed in the ' Dee,' I expect that its 

 velocity in still water will be one-eighteenth less than that of the ' Lightning' in 

 similar circumstances ; and it would require the engines of the ' Dee' to be 230 

 horse nominal power to render them of equal speed. The 'Dee' spreads above 

 water at an angle of about 50 degrees with the water line, to a width of about 



1 This is estimated from a vessel in use, and esteemed. 



