Are we asking too much from our radar reflectors? 

RYA Cruising Officer Carol Paddison talks about the limitations of radar reflectors and how keeping safe on the water is a team effort.

SOLAS Regulation V/19 requires all small craft to fit a radar reflector ‘if practicable’. The MCA specifies that a privately owned small craft should fit a radar reflector if practical and that it should be a big as possible. 

However, a radar reflector alone will not prevent another vessel putting a nasty dent in your boat. It is simply an aid that may improve your chances of being spotted by other vessels in your vicinity.

It helps to ensure that you show up on a ship’s radar display but this is by no means guaranteed; you may not always be readily visible on ship’s radars and thus you should always navigate with caution.  

We tend to expect more from our radar reflectors than they can actually deliver and there are two principle reasons why.

1. The S Band

SOLAS Chapter 5 requires that all vessels over 300GT carry X Band radar and all ships over 3000GT to also carry S Band radar as well, thus all commercial shipping should at least use X Band radar.

This is a good for us because passive radar reflectors perform much better in the X Band. However, in poor weather conditions, when we most need to be seen, bigger ships generally navigate using S band radar because it has far better penetration.

Most passive reflectors will only produce about a 1/10th of the response in the S band and therefore you could quite easily disappear in the clutter.

Active Radar Reflectors or Radar Target Enhancers (RTE) use technology to overcome this by receiving, amplifying and re-transmitting a radar signal but some may not work on S band.

This ensures a stronger return signal around the full 360° azimuth. Clearly such devices can be designed to work on one or more bands but they come with a price tag.

2. Consistent reflected radar energy

An important parameter of a radar reflector is the ‘echoing area’, or equivalent radar cross section (RCS), as this determines the amount of radar energy that is reflected back.

Unfortunately, the 1997 International Standards Organisation (ISO) performance standard for passive reflectors was later considered inadequate because the reflected energy was not required to be consistent around the full 360° azimuth and performance was significantly degraded when heeled; even then, many of the passive reflectors that were commercially available for recreational craft failed to meet it.

In 2004 the International Maritime Organisation revised the performance requirement.

The revision introduces more demanding performance requirements which must be maintained through angles of heel 10° either side of the vertical for vessels designed to operate with little heel (power craft for example) and 20° for other craft and sailing vessels; this is the concept of Stated Performance Level.

The new standard is also in 2 Parts; Part I for passive type reflectors and Part 2 for RTEs which were not specified in the 1997 ISO standard.

Regrettably, the improved performance standard cannot easily be packaged into the physical dimensions also set out in the standard at a price that many of us can afford. We are told that the reference reflector used by QinetiQ in their tests is handmade and costs in the order of £3000.

So where does that leave us?

Small boats can also fit radar and/or AIS. Both of these aids to navigation help you to detect other vessels. You can see the direction and speed they are moving and take action (in accordance with the COLREGs) to avoid them if necessary.

Such tools may of course help you to decide that there is no risk of collision and you don’t need to take any action.

The key is to sail defensively by which we mean to avoid creating a close encounter with another vessel in the first place. Ever been the stand on vessel and not sure of what the other vessel is going to do?

Avoiding a collision is a team effort

You cannot and should not rely on one single bit of kit to prevent a collision – radar, AISB transponders and radar reflectors are simply aids and all have their weaknesses.

Keeping a good lookout by all available means using your eyes and ears as well as any aids to navigation you may have on board and is a requirement of Rule 5 of the COLREG.

This together with a properly fitted radar reflector to help ships detect you (and if you’ve chosen to have one a radar or AIS B transponder), remains your best method of keeping yourself safe on the water.

Finally, it is worth knowing that many operators of radar systems use automatic guard zones set at 3nm to 5nm, to warn of approaching vessels and a consistent radar target response is important to trigger this function.

For a passive reflector to provide a potential detection range of 5nm it should be mounted at a minimum height of 4m above sea level to take it out of any wave obscuration effects.  

A radar reflector may not be a perfect piece of kit, but the RYA strongly recommends that boat owners permanently install, not just carry on-board, a radar reflector or RTE that offers the largest Radar Cross Section (RCS) and best performance possible for their vessel.

Carol Paddision RYA Cruising Officer

Further reading on the performance of radar reflectors can be found in the 2007 report by QinetiQ which highlights the significant weaknesses in the radar reflectors tested in the QinetiQ performance investigation.

 

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Article Published: May 31, 2012 10:58

Article Updated: May 31, 2012 15:55

 

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