292 NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE
the course the ship takes during the interval of stopping They
may balance, in which case the ship will go straight on; or any
one of the three may predominate and determine the course
of the ship. The utmost ef ect of these'influences when they all
act in conjunction—as when the screw is right-handed, the helm
starboarded, and the wind on the starboard side—is small as
compared with the influence of the rudder as it acts when the
ship is steaming ahead."
SHIP WITH HEADWAY/FULL AHEAD TO FULL ASTERN.
Discuss the Steering Effect of Propeller and Rudder,
This case may arise suddenly through force of circumstances to
avoid colliding with something close ahead. The turmoil in the pro-
peller aperture is rather confused but is something on the following
lines.
The normal current flowing aft past the rudder is interrupted by the
reversed screw (i) discharging water forward in opposition to it, and (11) by
inducing a forward flow which acts on the after side of the rudder.
These two forces gain strength as the screw continues to reverse and
eventually they predominate and swamp the normal flow due to headway,
but at first the turning effect of the rudder is doubtful and it should be
kept amidships, for then it won't be on the wrong side, bujb when the
vessel gets sternway it should be angled to one side or the other as
required. One thing is certain to happen at first, viz., the ship's head
will fall off to starboard.
The distance the ship will carry her headway is perhaps of more
importance in an emergency than the arc her head will describe when
the engines are rung from full ahead to full astern. It depends on the
ship's initial speed. The average 10-knot cargo vessel of 8000 tons
deadweight will probably bring up in about six times her length, and
if going half speed this distance will be reduced to about one-half. It
is interesting to note that when the backwash from the reversing pro-
peller reaches forward to about the navigating bridge the vessel's, head-
way is practically stopped, assuming the bridge to be a little forward of
amidships as it usually is. This approximation is a guide when stopping
the ship at night time for any purpose and no objects in sight.
To turn a single screw steamship short round.—A consideration of
what has already been stated will show that a steamer with a rigjtis-
Eanded propeller can be turned more easily with her head going co