234 Capt. McKonochie oii the ynost effective Employment 



wise, |)artly to support it against the lift of the engine, but chiefly to increase 

 the stability, and also prevent lee-way when crossing a breeze of wind. They 

 should, I think, be placed about two-thirds out from the keel, towards the 

 sides. 



Such a boat as this, whatever other qualities it might want or have, tfrould 

 be at least extraordinarily buoyant, and might be taken great liberties with, 

 both as relates to the circumstances in which it is placed, and the weight em- 

 barked in it. Its machinery sheuld (I think on the whole) consist of two engines, 

 arranfjed so that one only, on an emergency, could work the paddles ; although 

 it is worthy of remark, that this security against accident would be purchased 

 by other considerable sacrifices. Two engines are heavier, and more expen- 

 sive, than one of their united power, and are nothing like so powerful, because 

 the force of each merely concurs with the momentum of the other, insuring, 

 but not very materially adding to its effect. Still, as a security against 

 accident, two engines seem, at least in sea-going tugs, desirable*. The 

 pressure may be either high or low ; but whatever it is, there should be at 

 least a great reserve of pressure against emergencies ; and moderately high 

 pressure, used expansively, is the most economical, and has the greatest range 

 at its command. Whatever almost the power, it is desirable that the steam 

 should rather be supplied by several small boilers than by one or two large, 

 because small boilers can be made relatively stronger than large ; where 

 there are thus several, scarcely any accident could altogether disable the ma- 

 chinery ; and there is some economy in small boilers, — in favourable circum- 

 stances, they need not all be used together, — the greatest available quantity of 

 heat, according to Mr Dalton, is derivable from a fire not exceeding fourteen 

 inches depth, — and the shallower the water above the fire, the more readily 

 does the heat penetrate, and drive it off into steam. For the purpose of go- 

 ing both ways indifferently, the paddle-wheels and axle should be placed ex- 

 actly in the middle, between stem and stern ; and the more equally the rest 

 of the machinery is distributed along the floor, leaving the extremities light, 

 the easier the vessel will be. Perhaps one of the greatest defects of the ordi- 

 nary steam-boats in a sea-way is, that the Whole is huddled up in the least 

 possible space, and generally far forward, for the sake of accommodation. 



It will not be necessary to enter into the same detail with respect to the 

 vessel to be towed ; for the truth is, that, although better could easily be de- 

 vised, and, if the system gains ground, will certainly be employed, the hull 

 of any ordinary small merchant vessel would do to begin with. Her size 

 must be regulated by the power of her tug :— but it is very important to ob- 

 serve, that it is certain it may be what may appear at first sight very large, 



* It has been suggested to me, since the above was written, tliat two eiigincs could be embarlced 

 and used separately, or only together on particular occasions ; and that thus the security contem- 

 t^Iated above could be gainescl without habitual loss of power. There seems to be one rather strong 

 objectioil to this plan, viz. that it does not give the same certainty of effect when working, as two 

 engines fitted in the usual way, — one engine being liable, if it does not work very well, to hang on 

 its centre, and perhaps return, instead of going round ; and high pressure enghies, worked expan- 

 sively, are peculiarly liable to this, their power being nearly quite exhausted towards the termina- 

 tion of their stroke. Still the idea may deserve consideration, and would certainly give a consi- 

 derable saving, and much greater range of power to be used as circumstances might direct. The 

 wei^t would not either be greater than that of two engines on the usual plan. 



