4 EKMAN. ON DEAD-WATER. [norw. POL. EXP. 



In the Kattegat the phenomenon is sometimes less regular (see accounts 

 Nos. 13 and 14 as well as Fig. 14, PI. IV). As long as the ship's course 

 is between two certain points she may answer her helm quite willingly, but 

 she cannot be made to head a course beyond either of these two limits. 

 The wake and the "dead-water stripes" have often an assymetric direction. 

 The cause of this is, no doubt, to be ascribed to the lighter brackish wa- 

 ter running as a narrow surface-current on the top of the heavier sea-water, 

 so that the upper and the lower parts of the ship's body move in water of 

 different velocities. Such surface-currents were directly observed in two 

 cases mentioned below. It is evident that the two currents — especially if 

 the ship draws more water aft than forward — tend to turn her head in a 

 certain direction. To both sides of this direction she may be made to head, 

 though within certain limits, depending on the strength and direction of the 

 surface and under-currents, and of the wind. Thus the currents in the sea 

 are able to considerably modify the effects of the dead-water. It is very 

 probable that particular accidents mentioned by the mariners as "dead-water" 

 are mainly caused by such surface- and under-currents. Some Scandinavian 

 mariners apparently give the name of dead-water to various effects upon 

 their vessels, which cause them to lose their steerage. Thus, for instance, 

 when a vessel in a light wind, is affected by a whirl-pool or when she is 

 brought out of her course by the influence of currents of different directions, 

 she is sometimes said to have got into "dead-water" although the cause of 

 the mishap has nothing in common with this peculiar phenomenon. 



It was mentioned above (p. 3) that vessels run the risk of getting into 

 dead-water if moving at below a certain speed depending on the conditions 

 prevailing, but not when proceeding at higher speeds. In particular cases 

 even steamers have "taken dead-water", whereas, in certain places, only 

 sailing-vessels, in a very faint breeze, are exposed to it. It is therefore evi- 

 dent that dead-water may be of varying strength in different places and 

 under different conditions. Without further defining this notion, I will give 

 a summary of the experiences of several Scandinavian mariners as to 

 the strength of dead-water under different conditions. The explanation of 

 the different statements will be reserved for Chap. III. 



First of all, dead-water seems less effective the smaller be the difference 

 of density between the surface layer and the sea-water below, or the more 



