On Fri, 06 Jan 2006 00:34:49 -0500, Larry wrote:

AIS to the rescue! Need shore fixed stations with all up-to-date
obstruction data coming out of them....

And that will tell you about the 16 ft Boston Whaler fishing in the
fog bank right in front of you?

Wayne.B wrote in
:

And that will tell you about the 16 ft Boston Whaler fishing in the
fog bank right in front of you?



No, and neither will the radar scanner at 55 ft as some suggest to get long
range. Boston Whalers with little metal are hard to detect.

Of course, if we were to make $99 AIS transponders MANDATORY, problem
solved.

On Fri, 06 Jan 2006 23:38:05 -0500, Larry wrote:

No, and neither will the radar scanner at 55 ft as some suggest to get long
range. Boston Whalers with little metal are hard to detect.

======================================

We have no problem picking up small boats with the scanner at 24 ft.

It is unlikely that mandatory AIS will ever become a reality for boats
under 30 ft or so, perhaps even larger.

No, and neither will the radar scanner at 55 ft as some suggest to get long
range. Boston Whalers with little metal are hard to detect.




Wayne.B wrote:
We have no problem picking up small boats with the scanner at 24 ft.

It is unlikely that mandatory AIS will ever become a reality for boats
under 30 ft or so, perhaps even larger.


And if it is made mandatory for pleasure boats, how many
people will still not have it, or forget to turn it on, or
leave it broken?

DSK

i am reminded of the guy with an early handheld plotting GPS walking around
in ten foot circles saying, "look, it tracks me exactly".....pre SA! I am a
relative newcomer to radar and use a digital RADAR-PC setup and during the
day i can imagine i am seeing all manner of things that show up on my
screen...if it is flat calm and the gain is high enough and the sewa clutter
is OFF....but at night in the fog healed 20Deg that dot that appears for one
scan...then mis and then two scans again then gone will have you staring at
the screen instead of looking ahead to see if it is a contact or a wave or a
ghost reflection from your rigging or even the bouy at 90degrees from the
blip. What about sidelobe reflections which are again reflected and
recieved...they are only interpretable after the fact...not a priori..? they
are lower in intensity and can look like a small contact in any place. The
receiver knows only when it switched from transmit to receive [time] and the
radial angle of the antenae at that time so a reflected signal appears only
to have been recieved from a distance equivelent to the total pathlength and
in a direction in a straight line perp to the face of the antenae at that
moment of capture...a ghost image. Then when you get a circular series of
large contacts you may well wonder what semi circular beast is ahead of
you.... read a book about the propagation of radar microwaves and see all
the ways a blip can mislead you and thank God the guy you almost mowed over
didn;t have radar and was keeping a lookout. Radar assisted collision are a
significant reality. Real life radar is a tool that must be interpreted and
i am finding out it takes a LOT of interpretation and experience to be able
to rely on it more so than your eyes. The mainbang is suppressed so you
don;t see the big donut around your boat extending for 200ft on a 1/2 mile
range...if you are at 1/8th mile you might see a target at 50ft but only if
the mainbang is not supressed and the gain turned way down and the sea
clutter way up to exponentially deminish the gain applied to close returns.
As for styrofoam cups....the intensity of an electromagnetic wave falls off
in a cubic [3rd power] manner relative to distance and the reflected wave
similarly diminishes but the part reflected is only that portion perfectly
perpendicular to the antenae...as it dips and turns on a weaving mast even
less of it is oriented in a 'perfect' manner. The intensity of the emmitted
electromagnetic field recieived by the antenna is so small it is a marvel
that modern electronics can even discriminate it from the background noise.

Now the clincher....what portion on the emitted signal would a round
styrofoam cup reflect from half amile away? hint, styrofoam is not a
reflector of electromagnetic energy..is it an insulator and absorbs
microwave energy. the only reflection would be from moisture in a thin
lhorizontal line...perpendicular to the antena and the relfected signal is
likely a billionth of the emmitted signal at best. Granted there are
galenium arsenide semiconductor equiped ultra low noise receivers that could
discriminate that SNR but at a few thousand dollars in the hands of a
relatively untrained operator the pleasure boat operators radar.....it makes
for good bench racing stories but little more. AND...if you really are
detecting the water on a birds wings i suggest you tune and adjust the radar
to pick up and discriminate larger targets...else they will be lost in the
clutter
In the process of ruining a 'story' i hope to have saved someones life by
stimulating you to really learn what a radar can and can't do...repeatably.
Quod erat...you know the rest of the story.
rick

"DSK" wrote in message
...
No, and neither will the radar scanner at 55 ft as some suggest to get
long range. Boston Whalers with little metal are hard to detect.




Wayne.B wrote:
We have no problem picking up small boats with the scanner at 24 ft.

It is unlikely that mandatory AIS will ever become a reality for boats
under 30 ft or so, perhaps even larger.


And if it is made mandatory for pleasure boats, how many people will still
not have it, or forget to turn it on, or leave it broken?

DSK

Wayne.B wrote:
On Fri, 06 Jan 2006 23:38:05 -0500, Larry wrote:


No, and neither will the radar scanner at 55 ft as some suggest to get long
range. Boston Whalers with little metal are hard to detect.


======================================

We have no problem picking up small boats with the scanner at 24 ft.

It is unlikely that mandatory AIS will ever become a reality for boats
under 30 ft or so, perhaps even larger.

It won't be mandatory for everything. Kayaks, 14' alu boats, logs.
Radar is still better.

Gaz