ISO 8729 extends to
six pages and is available from HM Stationery Office, the pertinent
performance paragraphs are:
5.1.1 The maximum echoing area
of the radar reflector shall be at least 10m2
5.1.2 Its azimuthal polar diagrams
shall be such that its response over a total angle of 240 deg.
is not less that 2.5m2. The response shall not remain below this
level over any single angle of more than 10 deg.
5.1.3 These requirements shall
be assessed by reference to related azimuthal polar diagrams about
the reflectors vertical axis and tilted from the vertical at angles
not exceeding plus or minus 3 deg.
5.2 Reflecting pattern in vertical
plane The performance of the reflector up to at least plus or
minus 15 deg. from the horizontal shall be such that its response
at any inclination remains above 0.625m2 over a total angle of
at least 240deg.
(Paragraph 5.2 is commonly accepted as flawed
and was based on the performance of the 18” Octahedral.)
RORC - Royal Ocean Racing Club - ORC
- Offshore Racing Council, now part of ISAF.
These operate the Offshore Special Regulations
which prescribe the equipment etc., to be carried on Ocean Racing
Yachts. The relevant part is regulation 4.10 which reads:
4.10 Radar reflector A Radar
reflector shall be provided. If the radar reflector is octahedral
it must have a minimum diagonal measurement of 456mm (18”),
or if not octahedral must have a documented RCS (radar cross-section)
of not less that 10m2. The minimum effective height above water
is 4.0 m (13ft). Compliance with ISO 8729 is strongly recommended
as a minimum standard. In addition to (but not in place of) the
above, an RTE (Radar Target Enhancer) is recommended.
SOLAS Chapter V Regulation 19 para 2.1.7
(effective 01/07/2002)
Regulation 19 para.2.1.7 requires radar reflectors to be carried,
where practicable, by ships under 150 GT. For UK-flagged this
includes pleasure vessels.
The following notes gives further guidance
on the choice of a radar reflector for small vessels and supersede
Merchant Shipping Notice M.1638.
1.) Reflectors meeting the standards
laid down in British Standard BS 7380:1990 (ISO standard 8729:
1987) meet IMO performance standards*. Radar reflectors which
were type tested and approved to the earlier DOT Marine Radar
Reflector Specification, published in 1977, also comply with the
IMO standards.
2.) An important parameter of
a radar reflector is it's echoing area, or equivalent radar cross-section,
as this determines the amount of the radar energy which is reflected
back. Reflectors to the above standards have a maximum echoing
area of at least 10 m² with a minimum echoing area of at
least 2.5 m² over 240° of azimuth. Orientation of the
reflector must follow manufacturers recommendations if it is to
be effective.
3.) Regulation 19 takes account
of the fact that reflectors built to the above standards are relatively
large and may not be practical for fitting to smaller vessels.
The Agency considers that fitting reflectors meeting IMO standards
to vessels of 15m and above length should be practicable.
4.) Owners and operators of
craft vessels of less than 15m in length should fit reflectors
with the greatest echoing area practical. In all cases, the reflector
should be mounted as high as possible for maximum detection range,
following the manufacturer's instructions.
5.) It should be noted by Master
and Operators of all vessels that even the 10 m2 reflectors referred
to above will be difficult to detect in sea clutter on radar displays.
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 at Sea.
6.) Electronic radar target
enhancers are now marketed by some manufacturers. Radar enhancers
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 do not operate
in the radar “S” band.
7.) 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.
Paragraph 5 above confirms our view that radar
reflectors with an RCS of 10m2 or less are of little or no use
in real sea conditions.
See
http://www.mcga.gov.uk
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