NO. IB.] EXPLANATION OF THE DEAD-WATER PHENOMENON. Ill 



must certainly be a long and difficult work. I am therefore inclined to explain the 

 effect of these methods as very largely to be ascribed simply to the fact that 

 the tug stopped for a while, when making the manoeuvre. The mixing may 

 in addition have been of some little use, and an even greater effect in reducing 

 the resistance might be ascribed to interference between the systems of waves 

 created by the tug and by the vessel towed, when the tow-rope is shortened. 

 The effect of any of the expedients given in the list on p. 7 in reducing the 

 resistance may certainly he regarded as nil, as far as the effectiveness depends 

 on the mixing of the water-layers. 



It is said that a vessel sometimes gets loose from dead-water when passed 

 by a steamer (see accounts Nos. 8 and 13). So far as I can see, the only 

 possible explanation of this fact, is that the steamer has produced boundary- 

 waves which, on reaching the vessel, have diminished her resistance at a 

 favourable moment. It is however difficult to understand why a vessel not 

 in dead-water, should generate considerable boundary-waves; and altogether 

 these facts must be accounted among those not thoroughly explained, unless 

 we suppose they depended merely upon chance of some kind, or else that 

 the maximum resistance was very little more than the vessel's propelling force, 

 so that an exceedingly small start was sufficient to quite free her from the 

 dead-water. 



There is another very interesting method of getting rid of the dead-water, 

 which may often be very useful, and which is also confirmed by experience 

 (see Kapt. Meyer's account from the Congo, in the supplement). It is this: 

 simply go as near as possible to the shore, where the vessel has only 

 very little water under her keel. If the fresh-water layer is nearly as deep 

 as the vessel, or deeper, the salt-water layer will then have a very small 

 thickness, (or none); according to equation (3) p. 43 the maximum wave- 

 velocity will then in any case be very small, and the vessel will in consequence 

 easily get rid of the dead-water and may steer from the shore again, if there 

 is no risk of falling into it once more. Even if the fresh-water layer is only 

 about half as deep as the vessel, the resistance will be reduced in the same 

 way ; partly owing to the diminished maximum wave-velocity, and partly because 

 the vessel's body when reaching from the surface above to the bottom 

 below, will give to the water particles a nearly horizontal motion and 



