The study of the performance of marine radar reflectors, commissioned by the MAIB following the loss of the yacht Ouzo has been published - and it makes rather disturbing reading.
It warns: “It is essential for yachtsman to be aware that, notwithstanding the type of radar reflector fitted, in certain circumstances their craft may still not be readily visible on ships' radars and thus they should always navigate with caution.”
The tests were carried out by QinetiQ in a controlled environment, and the testers stress that while this gives a good comparison, it is not comprehensive: “It cannot take into account different radar parameters, clutter, target RCS (radar cross section)/range/aspect etc.”
The testers offer the following advice to yachtsmen:
- Fit the most effective and appropriate radar reflector for your circumstances
- If fitting a passive reflector, a simple but effective rule might be to fit the largest reflector that your boat can sensibly display
- Ensure your reflector is properly installed
Nine reflectors were chosen for testing and comparison, to represent a cross section of those available in the UK. They were: Plastimo 16” octahedral (approx £16), Plastimo 4” tube (£40), Davis Echomaster (£60), Viking Large Tri-Lens (£300), Viking Standard Tri-Lens (£130), Echomax 230 (£130), Firdell Blipper 210-7 (£130), Sea-Me (£500) and POLARef 11 (£2,000).
(The POLARef 11 is a precision radar target generally used for the calibration of radars: it is not designed to be fitted to yachts, but was included in the test as a baseline to demonstrate what can be achieved by a passive radar reflector.)
The Echomax 230 is the only one in the test which has been type approved to ISO8729, the ships and marine technology standard for marine radar reflectors, but it narrowly failed to meet that standard consistently during the test.
The conclusions of the test are as follows:
- The Sea-Me is a good example of an active reflector, exceeding the requirements of the current and future ISO 8729 at heel/elevation angles of up to 15°. It is also very small and light. Drawbacks are that it requires power to operate and it will only operate at X-Band and will offer no performance at S-Band.
(SOLAS Chapter 5 requires that all vessels over 300 tonnes carry an X-Band radar and all ships over 3,000 tonnes carry an S-Band radar as well. All the reflectors are designed to operate at X-Band, but passive reflectors will offer some performance at other frequencies, including S-Band. All the testing was performed at X-Band)
- The POLARef shows excellence is possible, but at a price. Technically it just fails to meet current ISO8729 or its replacement. Drawbacks are it is very costly and quite heavy at around 5kg. It could possibly be re-engineeered for commercial production which would reduce the price.
- The Large Tri-Lens performs well especially at larger angles of heel and elevation. It just falls short of ISO8729 but otherwise performs well. It is the heaviest reflector supplied for test at 5.5kg and costs around £300.
- The Echomax 230 narrowly failed to meet ISO 8729 during this testing but showed good peak and average RCS performance. The reflector is reasonably priced at £130 and weights 2.4 kg. The main drawback was a RCS drop-off above an elevation angle of 10°.
- The Firdell Blipper 210-7 narrowly failed to meet ISO 8729 during this testing but showed good peak and average RCS performance. The reflector is reasonably priced at £130 and weights 1.8 kg. The main drawback was a RCS drop-off above an elevation angle of 10°. (The Firdell Blipper 210-7 is slightly down on the Echomax 230 in terms of peak and average RCS but has a very similar stated performance level.)
- The Standard Tri Lens does not meet ISO8729 as the peak RCS was too low. However its consistent RCS response outperformed most of the other reflectors when heeled over beyond 10°. It is reasonably priced at £130 and weighs 2.5kg.
- The Plastimo 16” octahedral is inexpensive at £16 and lightweight at 0.65 kg but failed to meet ISO8729 in either tested position (upright and “catch rain”). It had reasonable peak and average performance, but wide nulls. Other drawbacks are that its mounting arrangement is by suspension only (often in an unfavourable position) and could be subject to damage.
- The Davis Echomaster failed to get close to ISO8729 during this testing. This reflector is priced at £60 and is lightweight. It can be mounted on a rod as well as by suspension (in the correct catch rain position.)
- The 4” tube reflector performed very poorly.
- The active Sea-Me, POLARef and the Standard or Large Tri Lens radar reflectors are the best reflectors at heel and elevation angles of over 10°.
The recommendations of the report are as follows:
- Yachtsmen should always fit a radar reflector that offers the largest RCS practicable for their vessel.
- The Radar reflector should have a minimum consistent RCS of 2m².
- The Sea-Me is the recommended product if power is available.
- If power is not available then the passive Large Tri Lens reflector is recommended.
- The 4” tube reflector is not considered suitable due to its poor performance. The 2” tube reflector is not suitable since the performance of this target will be even lower.
- Poorly performing radar reflectors should not be fitted as it is possible that the user could be lulled into a false sense of security.
To read the report in full visit www.maib.gov.uk
