NO. 15.] COLLECTIVE DESCRIPTION. 



water. It has happened, however, that steamers have been caught by it. It 

 is said that vessels do not run the risk of falling into dead-water when mov- 

 ing at above a certain speed, e. g. 3, 4, or 5 knots, according to conditions 

 prevailing. 



The phenomenon shows its simplest phase, when a steamer or a ship 

 in tow takes dead-water. There is, however, a difference in steering, between 

 screw-steamers and ships in tow; thanks to the influence of the screw the for- 

 mer are able to maintain their course; towed ships on the other hand, do not 

 answer their helm at all, and often in narrow waterways, the tow-rope must 

 be shortened, to prevent the ship from sheering off, with the consequent risk 

 of running ashore. 



If the engine be stopped, a ship in dead-water does not lose her motion 

 gradually, as under ordinary circumstances, but she stops short, and may 

 perhaps be sucked astern. In navigating the mouth of the river Glommen 

 similar and still more remarkable effects of dead-water have been observed. 

 As illustrated by Fig. 6, PI. IV, the vessel is followed by a long train of the 

 dead-water stripes described above. When the tug-boat is stopped and the 

 towed ship in consequence stops short, the dead-water stripes overtake her, 

 and, as they pass, the ship swings backwards and forwards, once for 

 each stripe that passes. In the same way, vessels made fast to the shore, 

 will be pushed up and down the river when a ship in dead-water has been 

 towed past them ; the power of the stripes being at times so violent as to tear 

 a vessel away from her moorings. 



Sailing-vessels, when caught by dead-water, usually do not answer their 

 helm and, in spite of the rudder and various manoeuvres with the sails, take 

 a certain course depending on the direction of the wind; often they run up 

 in the wind with sails shivering. Therefore, the loss of steerage is generally 

 the most troublesome effect of the dead-water on sailing-vessels, although in 

 particular cases, the vessel may be kept to her course with more or less 

 effort. Owing to the wind the aspect of the sea is often asymmetrical, the 

 stripe issuing from the windward side being best developed (see Fig. 12, PI. IV). 

 When the sea is rippled by the breeze the stripe on the windward side may 

 be invisible, whereas on the leeward side where the sea is smoother, it may 

 may still be seen. Often, however, the dead-water appears in its regular 

 aspect. 



