• Polytechnic Association. 865 



March 8, 1872. 



Prof. S. D. Tillman in the chair ; Robert Weir, Esq., Secretary. 



Danish Steam Navigation. 



By Prof. J. A. Whitney. 



The two steamers, Rolf and Thorvaldsen, are the first iron vessels 

 bnilt in Denmark that have visited this country. I passed about two 

 hours on the Thorvaldsen, and found her a staunch, well-built 

 steamer, registering 884 tons. The dimensions are 228 feet long, 

 thirty feet beam, and seventeen feet draft, when laden. The motive 

 power comprises two inverted vertical compound engines, each of 

 sixty horse-power, nominal, and connecting direct to the propeller 

 shaft ; the propeller has a diameter of thirteen feet. The boilers, 

 which are two in number, and worked at an average pressure of fifty- 

 five pounds per square inch, are of the tubular return type, and are 

 claimed to give a notable economy of fuel, from two and one-half to 

 three pounds per indicated horse-power per hour. Some features of 

 the boilers are worthy of general imitation, all the rivet holes being 

 drilled instead of punched, and the fire-boxes, or furnaces, being 

 turned to fit their places in the boiler shells, to which, by riveting, 

 they are secured by angle irons. Surface condensers are, of course, 

 employed, but instead of using the water fresh, as it comes from the 

 condensers, care is taken to add about seven ounces of salt water to 

 the gallon, which causes a scale, about the thickness of ordinary 

 paper, to form on the tubes and interior of the shells, and this pre- 

 vents the corrosion which would destroy the surfaces, if unprotected 

 from the copper salts dissolved by the water from the copper tubes 

 of the condenser, the pipes, etc. The steam, before reaching the 

 cylinders, is carried through a super-heater, situated in the uptake, 

 and heated by the escaping gases from the furnaces. The workman- 

 ship seems to be very good throughout, and creditable to the makers, 

 whose establishment in Copenhagen gives employment to about 1,100 

 operatives. 



I was informed by the engineer on board the Thorvaldsen that 

 Denmark is now building quite a number of iron steamers, some 

 registering 1,000 tons, which, considering that this branch of industry 

 was commenced in that country only some fifteen years ago, with 

 boats of fifty tons for the Baltic trade, is a decided proof of progress. 

 One iron vessel, smaller than the Thorvaldsen, but with engines of 

 the same style and power, makes fourteen knots an hour, running 

 between Copenhagen and Stettin. Another, the Dania, runs the dis- 

 [Ixst.] 55 



