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On Thu, 18 Sep 2008 19:21:19 -0700 (PDT),
wrote:

On Sep 18, 10:01 pm, wrote:
On Thu, 18 Sep 2008 16:27:23 -0700 (PDT),
wrote:

If someone has unlimited electrical power, is he likely to keep his
Radar on all the time when he is far offshore? Offshore, far from
anything else with a functioning radar system, what would prevent
someone from detecting a sailboat before a collision. Assume clear
weather.

Sailboats are notoriously poor reflectors. Even with RADAR reflectors
mounted on the mast, they don't always give much of a return.

Far offshore and away from known routes, it's usual to put the RADAR
on the "Watch" setting, which cycles it between standby and transmit
modes. You can set it to wake up and take a look around every 10
minutes, 20 minutes, whatever you want. This is a pretty standard
feature on most RADARS that you find on recreational vessels.

RADAR doesn't use nearly as much power as you seem to think. I sure
don't have unlimited electrical power on my sailboat with a 9.9 hp
outboard alternator as my only battery charger. I still use my RADAR
a lot. I just don't leave it in transmit mode when I'm not looking at
it.

Surely the sailboat would give some radar return before the collision
(assuming it is on). In clear conditions, what might cause somebody
to disregard a radar alarm? How often do radars return false echoes
in calm conditions? Just how "invisible" are most sailboats, say 30'
to radar without a reflector? Would objects such as downriggers or
other things aloft on the boat with radar cause false returns?
I see that some radars can be set to look only in a specified arc and
ignore things elsewhere. I assume that is to avoid looking behind and
concentrate on looking ahead. Why does this matter? Are false
returns enough of an issue to cause someone to only look ahead?

As I said, sailboats are often invisible to RADAR. Sometimes even a
RADAR reflector isn't enough to make them show up. This is a
universally well known fact of life.

The other factor is that reading and operating RADAR is not like
watching something literal on television. It's closer to knowing how
to read a medical xray. It takes knowlege coupled with a lot of
experience to have even an approximate idea of what you are looking
at. I use my RADAR in perfectly clear vis conditions in my home waters
almost all the time, just to keep those skills sharp. One thing you
learn is how retruns from different types of object appear. Most
navigation aids, for example, now have RADAR reflectors built into
their design. It increases the power of the return from those buoys
and makes them look like larger objects than they really are. Bear in
mind that they add thiose reflectors, even though the nav aids are
made of steel, and show up pretty well without the reflectors. It
helps to make them stand out on the screen. Slow moving sailboats may
appear to be stationary objects, even if they do give a return.

In other words, this isn't nearly as simple and cut&dry as you seem to
imagine.