In a message dated 12/9/2004 5:07:58 PM Eastern Standard Time,
mikem@yachtsdelivered.com writes:

We do have radar on our 43' "trawler" and this discussion on Fog , Radar ,
and Signals makes me ask.

Is our boat being see on radar readily enough ?  When is a radar reflector
recommended or needed?

I often see them on sail boats and wonder about our boat.  Where would it be
located?    Would it make sense to hang a radar reflector off of a radar mast?

Lynn
Grand Time
Tampa

DLLUV@aol.com
At 10:39 PM 12/9/04 -0500, you wrote:

This is a question worth some discussion.
The newer radars with 4 kw or better will pick up single seagulls on the
calm water up to 1/4 mile or so. A little farther, while flying.
In flocks up to 2 miles, especially with open arrays. By the time you get
to 6 or 8 kw or more they will show single pelicans at 1/2 mile. The
sensitivity is pretty great.
As sea surface roughness increases it becomes hard and harder to
differentiate any kind of real target from the sea clutter. And as the
range to the real target increases the target height has to increase in
order to be seen. Any target which lies near the physical horizon is likely
to be invisible to the radar, less so as power goes up, or as target
reflectivity increases.

Small boats of about 14' like cartoppers even made out of aluminum will
tend to disappear at 1 1/2 mile or so; UNLESS you are running power levels
of 6,8 or more kilowatts. In which case they will tend to show up as long
as they are above the horizon. At night, if running 4kw radar, a fish boat
with big lights comes over the horizon, your radar will not get a return
off of his light frame or supporting mast. He is about 8-9 miles away,
maybe a little farther. If you increase power to 8kw or better, then you
will most likely get a return off of that little bit. In effect you can see
his flood lights, but the radar cannot sense any return from the signal it
is bouncing off of the small metal parts at the top of his superstructure,
until you get into the higher power levels. Open array antennas will get
better images than closed radomes.

From this you can deduce a couple of things. Your radar is generally
capable of better work than any of us can generally put to effective use.
In the sense that if you could have it adjusted perfectly at all times and
sea surface conditions were calm and there were no interference from rain
and to some slight extent fog, then you would probably never have a target
get near you without your knowledge.

However, the range that you are using has a direct impact on the kinds and
sizes of targets that the radar will be effective at sensing. There is no
point in using a 6 mile scale to look for 14' outboard boats. If the boat
is nearby the sea clutter will mask it's presence and if it is beyond 1 1/2
miles, even in calm conditions, it will not be seen. As wave action and
spray increase the ability to detect such an object even on a 1 1/2 mile
scale will go down rapidly. Especially if it were coming directly towards
you with only a bow profile showing.

If your boat is anywhere above 30' or so, and in calm conditions, you
should show up on anyones radar without doubt; with one caveat. If the
other vessel is using a long range scale like 12 miles or so and you are
within about a mile or less then it is likely you will not be obvious,
notice the word, obvious on their radar. You will have gotten inside the
area that is mostly sea clutter on their radar. Since a 30' boat is likely
above the horizon out to about 2 1/2 miles, if they are using a 3 mile
scale, you should show up quite nicely until less than 1/2 mile. The danger
area is the circle surrounding the radar in which sea clutter predominates.
You can reduce sea clutter which will cause real targets to stand out by
increasing the level of the sea clutter suppression control. But, this has
the side effect of decreasing overall sensitivity in the sea clutter circle
area, which eventually will suppress even the real targets. Sea clutter
suppression(SCS) should be adjusted frequently and reduced to the minimum
practical under the conditions. If you have SCS in use then you have to
take this into account in estimating what kinds of targets will be visible
on your radar.

As you can see that even a wooden boat should show up pretty good if it is
of any size and above the horizon, in calm water.

Note: none of the above applies very well to the "S band" radars in use on
large ships. The frequency is such that only big objects show very well and
it is designed for long range. If they are running "X" band like the rest
of the small boat fleet and their radar is mounted way up with the S band
antenna, they may not have good sensing close into the ship. The "MV Coho"
ferry out of Port Angeles has an "X Band" radar mounted down low and out on
the bow as I recall, as it operates in an area of large numbers of small
boats.

I am quitting for the evening, but perhaps this subject will get some more
of my attention later. Radar enhancements(reflectors) are another subject.
But you can see that they have a use, but in my opinion are secondary to
proper usage of the radar equipment and only become a concern if you have
no radar yourself.

Mike

Capt. Mike Maurice
Tualatin(Portland), Oregon