266 NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

moment the ship to be almost stopped and rotated about her tuiniiig
centre 0

The stem sweeps round the circumference of the smaller circle and
the stern post round that of the larger one

i The Turning Circle.—It may be remarked here that when the rudder
is put hard over in a sudden emergency, say a man overboard at A, the
ship's turning pivot moves round on a circle and the vessel's keel makes
an angle with the periphery of her turning circle, as indicated in Figure 7,
her stern being thrown slightly outwards by the action of the rudder.
When at position B the helm should be eased and the vessel steered

V

V
V

\

\
A
i
i
i
Fig 7.—The Turning Circle.
for A, because, if the rudder be kept hard over, she will continue turning
through positions C and D. The turning circle will be uniform on the
second round. The diameter of the circle depends on several factors,
the length, breadth and draught of the ship, area of rudder, etc., but it
is usually about six or seven times the length of the vessel; the time
taken to complete the circle is also different for different ships but
averages about 8 minutes.
True and Apparent Wind.—When a ship is stopped the direction
indicated by a wind vane or by smoke from the funnel is the true wind*
During a dead calm no wind would be felt on board a stationary ship,
but when she gets under way a wind, or draught of air, will be felt
as if it were coming from dead ahead. This is an apparent wind caused
by the ship's progressive motion and this wind velocity win be equal to
the speed of the ship.