The only cases to which it does apply are when each of the two
vessels is end-on, or nearly end-on, to the other—in other words,
to cases in which, by day, each vessel sees the masts of the other in
a line, or nearly in a line, with her own; and, by night, to cases in
which each vessel is in such a position as to see both the sidelights
of the other.

It does not apply, by day, to cases in which a vessel sees another
ahead crossing her own course; or by night, to cases where the red
light of one vessel is opposed to the red light of the other, or where
the green light of one vessel is opposed to the green light of the other,
or where a red light without a green light, or a green light without
a red light, is seen ahead, or where both green and red lights are seen
anywhere but ahead.

Art. 19.—When two steam-vessels are crossing, so as to involve
risk of collision, the vessel which has the other on her own starboard
side shall keep out of the way of the other.

Art. 20.—When a steam-vessel and a sailing-vessel are proceeding
in such directions as to involve risk of collision, the steam-vessel
shall keep out of the way of the sailing-vessel.

Art. 21.—Where by any of these rules one of two vessels is to
keep out of the way, the other shall keep her course and speed.

Note.—When, in consequence of thick weather or other causes,
such vessel finds herself so close that collision cannot be avoided by
the action of the giving-way vessel alone, she also shall take such
action as will best aid to avert collision. (See Articles 27 and 29.)

Art. 22.—Every vessel which is directed by these rules to keep
out of the way of another vessel shall, if the circumstances of the
case admit, avoid crossing ahead of the other.

Art. 23.—Every steam-vessel which is directed by these rules to
keep out of the way of another vessel shall, on approaching her, if
necessary, slacken her speed, or stop, or reverse.

Art. 24.—Notwithstanding anything contained in these rules,
every vessel overtaking any other shall keep out of the way of the
overtaken vessel.

Every vessel coming up with another vessel from any direction
more than two points abaft her beam—i.e., in such a position with
reference to the vessel which she is overtaking that at night she would
be unable to see either of that vessel's sidelights—shall be deemed to
be an overtaking vessel; and no subsequent alteration of the bearing
between the two vessels shall make the overtaking vessel a crossing
vessel within the meaning of these rules, or relieve her of the duty
of keeping clear of the overtaken vessel until she is finally past and
clear.

As by day the overtaking vessel cannot always know with cer-
tainty whether she is forward or abaft this direction from the other
vessel, she should, if in doubt, assume that she is an overtaking vessel
and keep out of the way.

Art. 25.—In narrow channels every steam-vessel shall, when it is
safe and practicable, keep to that side of the fairway or mid-channel
which lies on the starboard side of such vessel.

Art. 26.—Sailing-vessels under way shall keep out of the way of
sailing-vessels or boats fishing with nets, or lines, or trawls. This
rule shall not give to any vessel or boat engaged in fishing the right
of obstructing a fairway used by vessels other than fishing vessels or
boats.

Art. 27.—In obeying and construing these rules, due regard shall
be had to all dangers of navigation and collision, and to any special
circumstances which may render a departure from the above rules
necessary in order to avoid immediate danger.

Sound Signals for Vessels in Sight of one another.

Art. 28.—The words “short blast” used in this article shall mean
a blast of about one second’s duration.

When vessels are in sight of one another, a steam-vessel under
way, in taking any course authorized or required by these rules, shall
indicate that course by the following signals on her whistle or siren,
viz.:—

One short blast to mean, “I am directing my course to star-
board.”

Two short blasts to mean, “I am directing my course to port.”

Three short blasts to mean, “My engines are going full speed
aftern.”