. THE EFFECT OF PROPELLERS ON THE STEERING OF VESSELS. 425 



ships, is thus neutralised, and must be regarded merely as a prolongation 

 of the ship. 



II. Ship going ahead, the screw working backwards and the helm 

 hard a-starboard. 



Result. The stern turns very decidedly to the right. 



Explanation. The rotation of the screw to the left presses the stern to 

 the left, and consequently the stem to the right ; the starboarded helm is 

 subjected to a pressure of water from behind, so that the after part of the 

 ship is doubly impelled to the left, the fore part being also with correspond- 

 ingly greater force pressed to the right. 



III. The ship going ahead, propeller working astern, helm hard a-port. 

 Result. The stern inclines slightly to the left. 



Explanation. The rotation of the screw to the left presses the after 

 part of the ship to the left ; on the other hand, the ported helm is under a 



pressure of water from behind which impels the stern to the right. The 

 operation of these two forces being of opposite nature, the vessel only 

 deviates slightly from the straight course, and then mostly with the stern 

 to the left. 



But as soon as headway is lost the force of the screw asserts itself so 

 much more that, in spite of the helm being ported, the stern turns to the 

 left and the bow to the right ; they turn in the same directions in a 

 stronger degree when the helm is amidships, and strongest of all when 

 the helm is starboarded. From the moment the ship begins to go astern 

 the screw must be regarded as the fore end or bow of the ship. After the 

 propeller, on the order " Full speed astern" being given, has made some few 

 revolutions, there comes a short period during which the helm can be 

 moved to either side with almost the same facility as when the vessel is 

 lying stationary, after the expiration of which it almost immediately 

 becomes necessary to use considerable force to work the helm. This is 

 due to the circumstance that immediately after the screw has made the 



