1840.] 



On Low Steam Power to Vessels, instead of Sails. 



239 



means of proceeding at a high speed along a few main lines, would 

 greatly increase the number of passengers on the subordinate ones. 



In all that has been said hitherto, it is supposed that the vessel has 

 no standing masts or rigging and never uses sails. She has three small 

 masts on board to be set up on the deck, with temporary rigging on 

 which can be set three lug sails containing in all about ^ of the full 

 spread of canvass for a ship of her tonnage ; these are merely kept in 

 case of an accident which deprives the vessel of the use of her steam 

 power. 



Whether it would be advisable to use these sails occasionally when 

 there was a steady leading wind is a separate question, which may now 

 be considered. 



The effect of a spread of canvass equal to ^ of that of a ship under 

 full sails, would be -| of her full speed, that is if under full sail she went 

 8 knotSj with a leading wind, she would run 5 knots with ^ of that quan- 

 tity of canvass when the wind is on the beam, or quarter, but with the 

 wind nearly aft, it would make a less difference than that. Further as 

 she would be able to carry such low and small sails, without any weight 

 of masts and yards above them, in a much heavier breeze than a sailing 

 ship could carry full sail, the average difference of rate in the two cases 

 would be much less than 5 to 8. There is a third point which would 

 still further reduce this difference, viz. that as such a vessel would never 

 have to beat or carry a heavy press of sail, she would of course be 

 built on the model of a steamer, that is with a light draft of water, and 

 great length, and consequently would with a leading wind require less 

 sail than such as are built on the model of a sailing vessel, to give her 

 the same speed. Allowing for these three considerations, the average 

 speed of such a vessel with a leading wind could not be taken at less 

 than I of that of a full rigged ship. Hence if a sailing vessel averaged 7 

 knots while running down a trade, the speed of the steamer from her 

 sails, and v/ithout using her engine, would be 5| knots and she might 

 therefore put out her fires in such circumstances, without going below 

 her average speed more than ^ knot, if the vessel of 380 tons has a 50 

 horse engine ; and with a gain of f knot if she has only a 30 horse 

 engine. Or she might use both steam and sails. In such cases, if she 

 could run 5| knots by wind only, and 5h knots by her engine alone, she 

 would have a speed of at least 7i knots, if she used both together. 

 That is, such a vessel with a 50 horse engine would by the additional 

 use of her sails run at least two knots above her average, and at least 

 one knot more than she would go with her engine and a strong wind 

 nearly aft and a following sea, but without sails. And such a vessel 



