214 REPORT — 1860. 



Appendix V. — Letter from Mr. Archbold, Engineer-in-Chief, U. S. Navy. 



Office of Eugineer-in-Chief, 

 Washington, D.C., May 12th, 1860. 



Sir, — I have the honour to transmit herewith, an abstract of the perform- 

 ance of the U. S. Steam-sloop ' Wyoming,' under steam alone, and under 

 steam and sail, on the passage from Philadelphia to Valparaiso, Chili, col- 

 lated from the logs of the engineer department of the ship. 



I am unable to give you any account of her performances under sail alone, 

 as in these logs no note of the sail is made when not under steam, and the 

 ship's logs are not sent to the Navy Department until the end of the cruise. 

 No trial of the ship was made in smooth water uninfluenced by sea from 

 which any data of value can be obtained. We do not try our ships at the 

 measured mile, the guarantees required of the contractors of the machinery 

 being on performances at sea, and for an extended length of time. The re- 

 sults for each day, as shown by the abstracts, are not assumed to be strictly 

 correct, as the data from which they are calculated are taken from the ordi- 

 nary observations of the engine-room, subject to errors and inaccuracies 

 unavoidable when the observers are so many, on duty for so short a time, 

 and when attention is necessarily engrossed for the greater portion of the 

 time in the care of the machinery. But as the errors are as likely to be on 

 the one side of the truth as the other, the average and means will not be far 

 from correct. 



Indicator diagrams were not found in the logs for each day, which will 

 account for the omissions in some of the columns, and there was but one set 

 taken during each twenty-four hours. The horse-power for the day was cal- 

 culated from these diagrams, correcting for the average revolutions for the 

 day ; and the horse-power for those days during which no diagrams were 

 taken, is calculated from those taken on days when the circumstances of wind 

 and sea were as nearly similar as could be found. The force of wind is 

 expressed in our logs by numbers, as follows: — 0, for calm ; 1, light air; 

 2, light breeze ; 3, gentle breeze ; 4, moderate breeze ; 5, fresh topgallant 

 breeze ; 6, strong single-reefed topsail breeze ; 7, moderate gale, or double- 

 reefed topsails ; 8, fresh gale, or three-reefed topsails ; 9, strong gale, or 

 close-reefed topsails and reefed courses ; 10, heavy gale, or close-reefed 

 maintopsails and reefed trysails; 11, storm trysails, or storm staysails; 12, 

 hurricane, or when no sail would stand. 



In the column headed " cut-off," the figures indicate the distance in inches 

 the steam followed the piston. 



The apparent discrepancy in the consumption of coal for the days between 

 October 25 and 31 inclusive, and some of the columns of which the coal 

 was the dividend, arises from the distilling apparatus having been in use, 

 making fresh water for ship's use; the amount of fuel due to the water 

 freshened having been deducted before dividing. It should be remarked, in 

 justice to our system of surface condensing, that the vacuum shown by these 

 abstracts is not so good by from 10 to 12 per cent, as has been obtained by 

 the same engines on former occasions, or by condensers of the same class in 

 other ships. 



I trust you will find in the abstracts everything necessary to the object 

 you have in view, and you may depend upon the truthfulness of the result 

 as nearly as they could be obtained from the data we have before us. We 

 have, in common with your Association, felt the want of systematized 

 authentic information upon steam-ship performance, and should feel obliged 

 by the receipt of any facts in relation to any of your modern vessels of war, 



