Page 114 - Collision Avoidance Rules Guide

at close distances. The Queen Mary-Curacao collision was considered
to have been caused partly by interaction yet the depth of water in the
area was about 120 metres.
Overtaking vessels should not attempt to pass too close in open
waters when there is plenty of room to manoeuvre. In narrow chan-
nels it may well be dangerous to overtake another vessel which is
itself moving at high speed.

Queen Mary-Curacao
No doubt the effect of the forces of interaction are very imperfectly known,
and one cannot impute to the captains of the two ships any expert or exact
knowledge of them, but I should have expected some allowance to have been
made for their coming into play, in the sense that the ships should not have
been allowed to approach so near to one another as to run a risk of their com-
ing into action. (Lord Porter, 1949, House of Lords)
When a ship is moving at any appreciable speed there is a region
of increased pressure in the water near the bow and stem and a region
of decreased pressure amidships. If two ships pass close to one
another on parallel courses forces of attraction and repulsion may
be experienced between them. The following diagrams indicate the
possible effects.
As the stem of vessel A overtakes the stem of vessel B there will
be a repulsive force between them so that there will be a tendency for
vessel B to swing her bows across the path of vessel A, (fig. I). The
Queen Mary-Curacao collision has been attributed to this effect.
Later the turning moment is reversed, and as the bows of the two
ships draw level vessel B will tend to swing outward as shown in fig. 2.

A A
.................
.................
.................... ......................
................... +
..................
...................
.............. L ..................
.................
Fig. 1 Fig. 2
B
A A .... -
................
.............
......................
........
....................
-
-
-
-
-
95