Annex 15 - Radar Reflectors

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.

Owners and operators should bear in mind that the smaller and less radar-conspicuous a vessel is, the more important it is to carry an effective radar reflector.

The following notes give further guidance on the choice and mounting of a radar reflector for small vessels.

1.) 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. (IMO Resolution 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.

2.) 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 m² RCS with a minimum echoing area of at least 2.5 m² 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 m² RCS in the X-band frequency and 0.5 m² 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 in MSC.164(78) should be referred to.)

3.) 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.

4.) 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.

5.) 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.

6.) 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 at Sea.

7.) 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.

8.) 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.

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