Reflectors meeting the technical standards laid down in British
Standard BS 7380:1990 (ISO standard 8729: 1987) will carry a
'Wheelmark' signifying that they have been type-approved to
this standard. In 2005, the IMO performance standard was revised.
MSC.164(78)) This will lead to a revised ISO technical standard
based on the 2005 IMO revision and is likely to be published
in 2008. Until the revised technical standard is published,
ISO 8729: 1987 will remain in force.
An important parameter of a radar reflector is its echoing area,
or equivalent radar cross-section (RCS), as this determines
the amount of the radar energy which is reflected back. Reflectors
to the current technical standard (ISO 8729: 1987) have a maximum
echoing area of at least 10 mē RCS with a minimum echoing area
of at least 2.5 mē RCS over 240° of azimuth. Orientation of
the reflector must follow manufacturers' recommendations if
it is to be effective. The revised IMO performance standard
requires reflectors have "stated performance levels" as follows:
Radar cross sections of at least 7.5 mē RCS in the X-band frequency
and 0.5 mē RCS in the S-band mounted at a minimum height of
4m above sea level. This performance level must be maintained
over at least 280° of azimuth and not fall below this level
(a "null") over any angle of more than 10°. There must be no
more than 20° between nulls. For sailing vessels the performance
level must be maintained up to at least 20° of heel, except
for multihull vessels which operate with little heel when this
minimum should be 10°. (The full text of the performance standard
should be referred to.)
The correct orientation of a radar reflector is extremely important.
The classic octehedral reflector (consisting of a number of
interlocking plates), should always be rigged in the "catch
rain" or "double catch rain" position. This means that one or
preferably two of the hollows between the plates face vertically
upwards. In the "catch rain" position maximum reflectivity is
given when the vessel is not heeled with deterioration as it
heels. In the "double catch rain" position one planar surface
should be aligned vertically along the vessel's axis. This allows
for improved reflectivity as the vessel heels to either side.
Mariners should be aware that the pre-drilled holes for rigging
the reflector are not always placed in the optimum position.
Regulation 19 takes account of the fact that reflectors built
to the above standards may not be practical for fitting to very
small vessels. However whenever physically possible reflectors
should meet the IMO standards.
Owners and operators of very small craft where fitting reflectors
meeting IMO standards is deemed impracticable should fit reflectors
with the greatest echoing area possible. In all cases the reflector
should be fitted as high as possible for maximum detection range,
following the manufacturer's instructions.
It should be noted by Masters and Operators of all vessels that
reflectors, even though they meet the relevant performance standards,
will be difficult to detect on radar displays in rough sea conditions
and in heavy rain (sea and rain clutter). Masters of all vessels
are reminded that this should be taken in to account when setting
lookouts and determining safe speed as required by Rules 5 and
6 of the International Regulations for the Prevention of Collisions
Electronic radar target enhancers are now available and
can be considered as "other means" in the Regulation. These
have a larger equivalent radar cross-section for a physically
smaller size than radar reflectors and produce a response on
a radar display, which is stronger and more consistent, but
does not increase the apparent size of the target. Some navigation
buoys are being fitted with electronic radar enhancers and seafarers
should be aware this improves their detection range. Mariners
should note that radar enhancers currently available (2007)
do not operate in the radar "S" band.
Owners and operators should note that under Regulation 18 equipment
meeting the requirements of Regulation 19 must be type approved.
However by virtue of Regulation 1.4, the Agency allows United
Kingdom vessels which are too small to fit reflectors meeting
the IMO standards to fit equipment suitable for the type and
size of vessel.