Marine Regulations & Rules
(Please note that the terms Stated Performance Level (SPL) and Maximum echoing are not related and should not be used for comparison)
Copyright restrictions prevent us from listing the specification in full.
Applies to SOLAS ChV and X and all ships to be fitted with passive and/or Active RTE, if practicable, and covers the frequencies 3GHz (S-Band) and 9GHz (X-Band) whose wave lengths are 10 and 3cm respectively.
The reflector must have a Stated Performance Level of 7.5M2 measured in meters radar cross section (M2RCS) of at least 7.5M2 in X band and 0.5M2 in S Band mounted a minimum 4 meters above sea level.
The SPL should be maintained over 280 degrees and not below this level over any single angle of more than 10 degrees - a null and not have any distances between nulls of less than 20 degrees.
For power driven vessels and vessels designed to operate with little heel ie catamaran/trimaran, this performance should be maintained through angles of (athwartships) heel 10 degrees either side of vertical.
For sailing vessels the 7.5M2 SPL should be maintained at 20 degrees of heel either side of the vertical.
Full copies of the specification can be obtained from ISO or HMO
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.)
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.
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.
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 Masters 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 allowsUnited 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.
The above seems to question the belief held by some sailors that only S band is used by Ocean going vessels. Rule 7(b) of the International Regulations for Avoiding Collisions at Sea states
(b) Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects.
X band is referred to as the collision avoidance frequency and in a Court of Law it would not help the Captains case in collision with another vessels if it were disclosed that the X band radar was either switched off or not being monitored.
ISAF Offshore Racing Rules 2012-2013
4.10 Radar Reflector
4.10.1 A passive Radar Reflector (that is, a Radar Reflector without any power) shall be provided
a) If a radar reflector is :
i octahedral with triangular plates making up each pocket it must have a minimum diagonal measurement of 456 mm (18in).
iii not octahedral it must have a documented RCS (radar cross-section) of not less than 10 m2 at
0° elevation and be capable of performance around 360° in azimuth.
The minimum effective height above water is 4.0 m (13 ft).
b) The passive and active devices referred to in thesenotes and in 4.10.1 and 4.10.2 above are primarilyintended for use in the X (9GHz) band
4.10.2 The most effective radar response from a yacht may be provided by an RTE (Radar Target Enhancer) which may be on board in addition to the required passive reflector. An RTE should conform to ISO 8729-2:2009. An RTE is strongly recommended.
a) An RTE shall be provided in compliance with ISO8729-2:2009 or ITU-R 1176
b) The display of a passive reflector or the operation of an RTE is for the person in charge to decide according to prevailing conditions.
4.10.3 When available, a passive radar reflector in compliance with ISO8729-1:2010 will offer improved performance over earlier models and has a size typified by a cylinder of not more than weight 5kg, height 750mm and diameter 300mm.
4.10.4 S (3GHz) band radar is often used by ships in bad weather to complement X (9GHz) band radar. On S (3GHz) band a passive reflector offers about 1/10 the response obtained on the X (9GHz) band. Unless specifically designed to operate in the S(3GHz) band, an RTE will provide no response at all. (This has now been superceded as there now RTEs available which do respond to both S and X band radar and meet ISO 8729-2)