So you've entered your survival craft, but now you need to be rescued.
Even with ship searching in the correct area, narrowing down your exact location
can be a real challenge.
That's where a SART can help. They attract the attention of passing vessels
by actually drawing on their radar screen. Activated correctly they point the
searchers in the right direction, increasing your chances of being rescued
SART stands for search and rescue transponder. It is an active device, meaning
it transmits a signal to draw attention to itself. It is triggered when it detects
a pulse from a radar. As soon as it does, it transmits multiple pulses straight
back, painting a series of twelve distinctive
echoes on the screen, guiding the searching vessel towards its location.
They operate at nine GHz, which means they show up on an x-band
three cm radar screen.
Day to day, the units themselves require very little
maintenance. All you need to do is make sure they're clean and dry, check the
battery expiry date, and test them monthly. Every unit is different so you
do need to check the instructions on the unit. You can just slide the switch
to the test position to temporarily activate it. It will indicate whether the
internal test is successful, often with a light. If you have radar you can also
check the screen to check it's responding correctly.
In an actual emergency you need to make sure you take it with you.
There is no rush to activate it, especially if you're still close to your
original vessel. That will paint a large echo anyway and may even block the
SARTs transmission. Once you are clear you can then set it up.
To activate the SART, you normally just need to remove a pin. It should then
indicate to you that it's working. Once active, it needs to be mounted as high as
possible. The higher it is the further away it will be detected.
In the water you can expect only a mile or so.
On the floor of a life raft is not much better
maybe two or three miles if you're lucky.
But mounting 1 meter high it must be
able to be detected at least 5 miles away.
One meter is the height of IMO performance standards and it should have
been designed to comply with that.
It should have enough battery to last 96 hours in
standby mode (four days), and eight hours in transmission mode. Of course it
should only actually be in transmission mode when another vessel is close enough to detect it.
If you have multiple starts it's important to only activate one at a time.
Using one ensures that the radar return maintains its distinctive nature
and can't be confused with another echo. The other point to note is to never use
a SART and a radar reflector close together.
There's always a chance that the radar reflector will block the SART's signal.
Once it's all set up you just need to wait for a radar to be close enough to
activate the SART.
For the approaching vessel, the first sign that there's a salt operating is the
characteristic dots on their radar screen. At long-range these shows twelve
dots in a line, originating from the sart's location.
The first return is the SART itself, and the further dots are the extra echos generated by the SART.
The extra echoes will be 0.6 miles apart, so they can be seen best on a six or a
twelve mile range setting as they'll span a total is 7.2 miles across the screen.
The precise range that the SART is detected does vary. We've already spoken
about the importance of mounting height. Another major factor is the height of
the radar looking for it. For surface craft with scanner height of 15 meters, you can
expect those performance standards of 5 miles for a correctly mounted start.
This then increases for bigger ships with higher radar scanners.
The greatest range will be from aircraft searching around 3,000 feet. They may pick it up at even 40 miles away.
Once the SART begins generating these extra echoes, it indicates to its user
that it's under interrogation. Often this is by a flashing light or an audible
signal. It tells the survivors that an x-band radar operating nearby and should
act as somewhat of a morale boost. Knowing that there are vessels close by
is also good indication that traditional flares will be spotted. Even at maximum
range rocket parachute flares should still be visible to the vessel that has
activated the SART. Hopefully now the SART, or maybe even the flares, have attracted
the attention of the other vessel. They can use the shape of the echo to locate
the survival craft. As they draw nearer the dots on their radar screen become arcs.
This is because the scanner is picking up the returns across a larger angle.
The closer it gets the larger the angle that the scanner can detect the SART
so the larger the arcs become on the screen. Eventually the arcs become
full circles, showing that the approaching vessel is now very close to
the SARTs location. If all goes well, the survival craft should be clearly visible
and survivors can be rescued
They're not cheap, but if you're bobbing in a survival craft and need rescuing, you'll wish you had one.