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Return to Radar page
There are a few very important factors
to be taken into account when selecting a radar reflector for an
offshore cruising boat. Offshore being the operative word, because a
different or better radar reflector may be required offshore
because ships use two different types of radar depending on
whether they are coastal or offshore, and also the weather at the time.
When a ship is close to the shore it may use X-Band radar, and when it
is deep-sea it may use S-Band radar. This raises a
rather uncomfortable reality for cruising boats, in that most radar
reflectors are good with X-Band radar but are not necessarily so good at reflecting
S-Band. I am told that the new IMO regulations require good response in
both bands, newer radar reflectors are about to be launched (Jan 2005),
so keep an eye on new products.
There is another angle to this and that is simply that in good
weather deep-sea ships often do not use radar at all. So we may even
be putting too much trust in our radar reflectors. Having said that,
we should do everything we can to minimise the risk of being run-down,
and don't forget that in bad weather such as heavy rain, fog etc ships
will be using their radar and it would be very nice if they were able to
see us.
When cruising short handed, keeping a thorough 24 hour watch is very demanding and we may all
be guilty of at least occasionally not being as thorough as we should
especially when we are very tired. Don't forget that fibreglass and
wooden boats are extremely poor at reflecting radar. Having a good
quality reflector may help in being seen when our guard is down.
Unfortunately when choosing a radar
reflector many people are using the wrong criteria to select a device.
The worst of these is size, trying to get the smallest device to perform
a task that is ideally performed by a large unit is a bit like
complaining that a parachute is too big and heavy and we want a smaller one. The physical size of a radar reflector
provides us with a bit of a conundrum, none of us really want a very
large cumbersome and drag inducing device in our rigging but the dilemma
is that for radar reflector to perform its function well it needs to be
fairly large. Manufacturers' have come up with clever ways of trying
to return a good echo from a small device. It is important
to carefully study the figures for each design, check the test results
where available and compare them with other designs. Most manufacturers
will supply test data if requested.
An ideal radar
reflector should reflect the radar signal through 360 degrees at large
and varying angles of heel. When viewing the test figures of the various
models available it will be seen that very few radar reflectors are
actually capable of returning a signal through the full 360 degree
spectrum especially when heeling, but even when they are not heeling! It
will also be noticed that standards have been set by certain authorities
that do not require 360 degree performance, which probably reflects on
the difficulty on producing such a radar reflector.
It should also take into consideration
that regulations may apply to yachts in certain countries regarding the
size and type of radar reflector required, you should check the regulations for your home
country.
There are several different
technologies to choose from; there are the standard passive reflectors
which themselves use different technologies and then there are some
active systems which require a power supply to enhance and return an
echo.
The choice of a radar reflector will depend on
many factors such as the size of the vessel, regulations, personal
preference and the size of the budget.
Also new technologies are emerging and although the new type of
reflectors look very good, we need to see some good independent tests as
these new models hit the market. Some vessels may spend most of
their time coastal cruising and others may plan to spend more time offshore which may affect the choice of radar
reflector.
The following is from the UK
Maritime and Coastguard Agency (MCA) website:
This website contains the text of the MCA publication Safety of
Navigation - Implementing SOLAS Chapter V, 2002 which is referenced in
the Merchant Shipping (Safety of Navigation) Regulations 2002.
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 ANNEX
15 - Radar Reflectors |
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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 m_ 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.
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