STEERING  AND  SAILING RULES

211

To be practical we must not expect to be able, under the varying condi-
tions arising at sea, to treat the J&ules with mathematical exactness. We
can, however, establish one or two general principles which, properly
appreciated, will afford valuable help to beginners. A diagram and
explanation will show the truth of the preliminary paragraph.
Suppose A and B to be two vessels approaching each other in the
directions A 0 and B C respectively. Their courses cross at C, and if
they both reach this point at the same time a collision must occur If
they are proceeding so as to reach the point C together their speeds must
be proportional to their respective distances from G. Thus, in the dia-
gram, A being the farther vessel from the collision point, her speed must

Fig   1.
be proportionally greater than that of B to cause her to reach C at
the same time. Assuming that this is the case; when A has sailed
one-third of her distance from C and is at ai} B will also have sailed one-
third of her distance from O and will be at B^ also when A has completed
half her distance from O and is at A^ B will have covered half her
distance from € and will be at B2, and so on.
If lines are drawn joining these corresponding positions, it will be
seen that they are parallel, thus showing that the bearings of the two
vessels from each other would not appreciably alter if they were
approaching in such a manner as to involve risk of collision.
If you see both side-lights of another vessel in any direction, youi
own vessel is in the act of passing the collision point. Also it is clear