prolonged, one short, one prolonged, and one
short blast, in that order. The Inland Rules for
overtaking vessels apply only to power-driven
vessels; the International Rules apply to all
A vessel that reaches agreement with another vessel
in a meeting, crossing, or overtaking situation by using
as prescribed by the
Bridge-to-Bridge Radiotelephone Act (85 Stat. 165; 33
U.S.C. 1207), is not obligated to sound the whistle
signals prescribed by this rule, but may do so. If
agreement is not reached, then whistle signals must be
exchanged in a timely manner and will prevail.
Conduct of Vessels in Restricted Visibility, Rule
20C, of both Inland and International Rules states that
the lights prescribed by the rules are to be exhibited in
restricted visibility. Rule 35 of both Inland and
International Rules states that the required sound signals
are to be sounded in or near an area of restricted
visibility. Inland and International Rule 19 applies to
vessels not in sight of one another when navigating in
or near an area of restricted visibility.
Before radar, the regulations depended almost
solely on the fog signal; vessels in fog sounded fog
signals and when other vessels heard them, they
stopped. The increasing use of radar today has resulted
in a supplementation to the existing regulations.
In 1960, a radar annex was appended to the
International Rules; it was ultimately incorporated in
In 1980, the word fog was discarded and replaced
by the term restricted visibility. The International Rules
today make it clear that vessels must maintain a proper
The rules make it obvious that radar is NOT a
substitute for a proper lookout. The courts have ruled
that dependable radar equipment must be turned on and
intelligent use made of it.
Rule 19E requires a vessel hearing a fog signal of
another vessel to reduce its speed, to bare steerageway,
and to proceed with caution.
No defined distance has been established regarding
visibility for sounding fog signals. Three miles has been
recommended for all vessels over 50 meters long. The
rules prescribe three types of devices: a whistle (for
vessels underway), and a bell and a gong (for vessels
anchored or aground). A whistle requires either a
prolonged blast of 4-6 seconds or one short blast. A bell
requires a 5-second rapid ringing. And a gong requires
a 5-second rapid sounding. International Rules require
a 2-minute interval between warning signals.
The fog signals for inland and international waters
(COLREGs) are very similar but there are two
exceptions. First, the Inland Rules do not provide for a
vessel constrained by draft; and second, they do not
require small vessels in specifically designated
anchorages to sound fog signals.
Small boats, as well as larger vessels, are required
to signal. A boat coxswain must have a foghorn in the
boat at all times. Motorboats must be outfitted with an
efficient whistle, horn, or other sound-producing device.
It should be noted that because a boat is exempt
from some specific requirement of the rules, it is not
excused from complying with the rules in all other
The sound signals in restricted visibility for the
International and Inland Rules are very similar. In this
part of the text, only the Inland Rules will be presented.
Any differences between the International and Inland
Rules will be noted.
In or near an area of restricted visibility, whether by
day or night, the signals prescribed in this rule will be
used as follows:
A power-driven vessel making way through the
water must sound at intervals of not more than 2 minutes
one prolonged blast.
A power-driven vessel underway, but stopped and
making no way through the water, will sound at intervals
of not more than 2 minutes two prolonged blasts in
succession with an interval of about 2 seconds between
A vessel not under command; a vessel restricted in
ability to maneuver, whether underway or at anchor; a
sailing vessel; a vessel engaged in fishing, whether
underway or at anchor; and a vessel engaged in towing
or pushing another vessel will sound at intervals of not
more than 2 minutes, three blasts in succession; namely,
one prolonged followed by two short blasts.