Helwig F. Van Der Grinten

Master Mariner

Notes on Shiphandling

These notes document some observations and recommendations concerning various aspects of shiphandling which may be of general interest to those involved in navigating and maneuvering ships. They are prepared as part of the ACDUTRA service of the author.

WIND EFFECTS


Shiphandling instructors use a rule-of-thumb which equates 30 knots of wind to the
effect of I knot of current on a maneuvering ship. This relationship is based on
Bernoulli's Theorem as applied to the difference in the densities of air and water. It
puts the effect in knots (C) equal to the square of the wind velocity in knots (V) divided
by 900 knots:

C = V Squared/900 knots This relationship can be very useful to navigators in
estimating the effects of wind on the course and speed of a ship, but this fact does not
seem to be generally known or applied by them. It is not mentioned in any of the
standard navigation reference books. The author pro- poses to promulgate this
information to appropriate publishers of navigational information.



MAN OVERBOARD MANEUVERING

Traditional doctrine on maneuvering to recover a man overboard teaches that the rudder should be immediately placed hard over to kick the stem away from the side over which the man fell. Because high-speed ships will be well clear of the man before the rudder takes effect, this automatic response is no longer advocated. Conning officers are now encouraged to evaluate all conditions which will effect the recovery before putting the rudder over.

A maneuver which will rapidly return most ships to the position of a man overboard is the Anderson one turn method. This method is particularly useful if the man is in sight. One thing which has been consistently overlooked in describing how to execute this maneuver is: how best to keep the man in sight. The author has learned from running drills that it is extremely important to avoid losing sight of the man in the glare of the sun. Losing sight of the man overboard while executing this- turn can double the time required to maneuver. This can easily be prevented by always turning the ship towards the sun. If this is done, the sun will remain behind the conning officer as he faces the man overboard. Consequently it will be more likely that he will be able to check the swing of the vessel and commence backing down at the right moment (see Figure 1).