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would remain dark, but when the Echomax antenna is slightly taller
searchlight passed over there and thinner than the Sea-Me and
would be a single, dazzling has a slightly smaller control box.
refl ection, provided the mirror is at Both operate on the X-band of
the correct angle. frequencies (9.32GHz – 9.5GHz)
PBO’s on-
Adding an RTE takes this one used by small boat radar and also
step further. Instead of a mirror, by ships (who operate it in
imagine a single, extremely bright conjunction with the lower
lamp fi tted to the black object so frequency S-band) and both offer water test
that it can shine out in all the option to fi t an external alarm
directions. Most of the time it is which sounds when the unit At close quarters an RTE often how easy it was to track the RIB
switched off, but as soon as it detects a radar pulse, a useful makes little difference, as the without an RTE by noting down
detects the searchlight it switches feature on ocean passages. This is radar returns from a small boat how far away the RIB had
on. Unlike the mirror, it shines just backed up by a visual alarm in are still consistent enough to reached when the radar’s
as strongly whatever angle the each case, and Echomax add an paint regularly on the screen. MARPA system lost lock.
searchlight comes from. That’s the audible alarm in the control box. Where an RTE starts to be of With no RTE active, the RIB
true advantage of an RTE: even if However, reading further into the signifi cant benefi t is at longer reached four miles before we lost
the radar is only weakly received, specifi cation sheet reveals some ranges, where the returns are lock. We then switched on the
the RTE will send a strong pulse signifi cant differences. Where Sea- starting to become erratic. Sea-Me, which extended this
back to the receiver, increasing the Me quote a radar cross section of To test this, we mounted both range to 5.5 miles. Carrying out
number of times the yacht is 42.57m
when the antenna is antennas on 2.3m windsurf the same test with the Echomax
reliably ‘painted’ on the radar upright, Echomax quote 111.36m
. masts and lashed them to the allowed the RIB to continue to a
screen. And that has all sorts of At 20° heel, Sea-Me’s RCS is A-frame of a RIB. We then range of 6.7 miles before we lost
additional benefi ts: you are not 9.03m
, while Echomax claim headed out for open water to the lock, a signifi cant improvement
only more visible to a human radar 20.80m
. It should be noted that east of the Isle of Wight, pursued and very close to our radar
operator, you are also more likely both products exceed ISO8729-2, by Trinity Star, a Nelson 42 horizon of around 6.5 miles.
to be tracked by the ARPA which requires a minimum RCS of owned by Alan Watson of Trinity We then tested the units for
(Automatic Radar Plotting Aid) 7.5m
at 10° heel for motorboats Nautical Training and equipped performance at different angles
systems fi tted to ships, which need and 20° heel for yachts. with a Raymarine HD radar with a of heel by deliberately tilting
a ratio of around 50% successful On paper then, it looks like the 48in, 4kW open array scanner. each mast in increments of 10° at
paints to reliably track a target. Echomax should outperform the Once at No Man’s Land Fort, a range of four miles. One of the
Sea-Me, but theory and reality can when the echoes from other advantages of Raymarine’s HD
Echomax and Sea-Me differ so we took both units out to vessels became fewer and radar is it allows you to assess
Visually, the Echomax and Sea-Me test their maximum range and how farther between, we fi rst tested the strength of an echo on the
products are pretty similar: the they perform when heeled.
Echomax and Sea-Me specifi cations
Echomax Active-X Sea-Me
RCS at 0° (m
) 111.36 42.57
RCS at 10° (m
) 78.96 24.87
RCS at 20° (m
) 20.80 9.03
EIRP (transmit power) 1W typical 630mW max
Standby current (mA) 15 72.7
Transmit current (mA)* 290 199
Antenna size (mm) 478 x 40.5 416 x 50
Price £539.35 £513.83
* this is the current drawn when the RTE is continuously transmitting. Where there are fewer
radars, the current will be signifi cantly lower – Echomax quote 23mA for fi ve radars in the area and
The Raymarine HD radar shows echoes as red, yellow or green
32mA for 10 radars. according to their strength
Calculating Radar
slab-sided container ship will have the stealth ship, the sphere used
a huge RCS when side-on to the to model the RCS of the container
Cross Section (RCS)
radar, but a stealth vessel of the ship would be large, bigger than
same size with surfaces angled to the ship itself, as the slab sides of
refl ect incident radar pulses away the ship form a near-perfect
■ To calculate the RCS of a The choice of a sphere is due to from the receiver will either not refl ector. For the stealth vessel,
vessel, you model it as a sphere its even response – with no sharp appear at all or have a tiny radar the sphere would be much
that would have the same radar corners it consistently refl ects signature that could be from a smaller and hence have greater
signature as the vessel. A good radar pulses of any frequency in a much smaller vessel. Imagine a curvature, resulting in a smaller
yacht radar refl ector might have a predictable pattern at any angle. cone pointing directly towards the area at an appropriate angle to
stated RCS of 2m
, which is For detection by radar, the radar scanner – it could be refl ect the radar signal to the
equivalent to a sphere of 1.6m crucial factor is how the surfaces physically enormous, but because receiver. In either case, the useful
diameter. The Sea-Me’s stated of the object to be detected are all the surfaces are angled to refl ective area of the sphere
RCS at 0° heel is 42.57m
, positioned with respect to the refl ect pulses away from the cannot exceed the size of the
equivalent to a 7.4m diameter incoming pulses, which is why a receiver it would have no radar vessel. It’s impossible to make an
sphere, while the equivalent passive radar refl ector aims to signature at all. object look larger than it really is –
sphere for the Echomax’s present as many fl at surfaces at Using the sphere model in the all you can do is make it a better
RCS measures 11.9m. as many angles as possible. A cases of the container ship and or worse refl ector.
50 Practical Boat Owner 513 September 2009 •
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