50 BULLETIN 127, UNITED STATES NATIONAL MUSEUM. 



The hull is built as nearly like the original as present data give 

 information. The original boat was navigated in the harbor of 

 New York in 1804, and had an average velocity of 4 miles an hour, 

 and for a short distance at the rate of 7 to 8 miles an hour. 

 Made in the Museum. Cat. No. 160,306 U.S.N.M. 



Original twin-screw propeller steam engine and boiler designed" and 

 built by Col. John Stevens. 



A high-pressure, single-cylinder noncondensing engine, cylinder 

 4^ inches in diameter with a 9-inch stroke. 



Colonel Stevens' plan for working twin screws by a single cylin- 

 der is the most simple one that could be devised. The reaction 

 of the connecting rods against each other at their junction with the 

 piston rod develops a parallel motion, as slides would do, to keep the 

 rod in alignment. (When the screw propeller came into use, after 



FIG. 7. JOHX STEVENS' TWIN-SCREW STEAMBOAT. 



a lapse of nearly 40 years, this plan of a single cylinder for twin 

 screws was revived in this country and abroad, being known in 

 France as the " Etoile engine.") The valves on the engine are 

 formed by two-Avay cocks, a modification of the single-way cocks 

 used by Savery and Newcomen, one cock at each end of the cylinder 

 answering both for the admission and the exhaust of steam. The 

 valve motion is derived from a crank on the inboard end of one of 

 the propeller shafts. This crank works a rack, the teeth of which 

 mesh into those of wheels on the plugs of the two-way cocks, the 

 motion being similar to the toothed rack and segment of a wheel 

 which Watt used in one of his first engines to raise his conical valves. 



The boiler is one form of the multitubular boilers patented by 

 Stevens. It has 28 copper tubes, each 1^ inches in diameter and 18 

 inches long, 14 tubes projecting from each side of a rectangular chest. 

 The grate is placed at the end of one set of tubes, and the flame 

 passes around these tubes and then under tlie chest and around the 

 tubes at the other end to the smokestack. 



The following extract in relation to this twin-screw vessel is from 

 a paper by Dr. James Renwick, written in 1858, addressed to 

 Frederick De Peyster, of New York, and read by the latter at a meet- 



