NOTING Article 16(i) of the IMCO Convention concerning the functions of the Assembly,
CONSIDERING the need to restrict the noise levels at listening posts in
vessels in order to ensure an adequate probability of hearing a whistle at the
audibility range given in the table of paragraph 1(c) of Annex III to the International Regulations for preventing Collisions at Sea,
1972,
HAVING EXAMINED the Recommendation on Methods of Measuring Noise Levels at Listening
Posts adopted by the Maritime Safety Committee at its thirty-second session.
RECOMMENDS that the method for measuring the noise levels at listening posts should be as
follow:
- (a) a precision sound level meter according to IEC - Publication No. 179 should
be used in conjunction with an octave-band filter according to IEC - Publication
No. 225. The microphone should be equipped with a windscreen of known
transmission characteristic and an extension cable. At the beginning and the end
of each series of measurements the calibration of the sound level meter should
be checked with a standard sound source (e.g. a pistonphone) according to the
manufacturer's instructions;
-
(b) all readings should be taken with the dynamic characteristic "slow". The
average of the maximum values observed during a period of ten seconds when
the vessel is making way at ¾ speed will be regarded as the prevailing noise
level. On bridge wings the measurements should be on the lee-side;
-
(c) the microphone should if possible bo so placed that, during the
measurements, it is separated by a distance of at least 1.5 m from any
substantial reflecting or obstructing surface;
-
(d) an average value should be determined in the area of the usual listening
position from measurements made in at least three different microphones
positions separated by at least 0.5 m from one another and approximately at
the average height of ear of normal listeners;
-
(e) as far as practibale, measurements should be made in coditions of wind
speed between 5 knots and 10 knots:
- (i) with the wind ahead,
-
(ii) with the wind astearn, and
-
(iii) with the apparent wind successively on both beams and the
listening position on the corresponding lee-side of the vessel;
-
(f) whether or not these recommended conditions can be achieved, the
prevailing wind speed and direction and the course of the vessel should be
recorded;
-
(g) furthermore, a record should be kept of the state of the sea and of the
condition of loading of the vessel,
FURTHER RECOMMENDS that Administration should institute programmes of measurements in
accordance with the above, within the limit of their capabilities, in order that
evidence may be collected on the noise levels currently experienced at listening posts,
both on existing vessels and on new vessels when brought into service. Administrations
are invited to submit the results of such measurements to the Organization for
consideration by the appropriate sub-committee(s),
ADOPTS provisional guidelines on maximum acceptable noise levels at listening
posts, the text of which appears in the Appendix to this Recommendation.