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?

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?

How far offshore and how far from known routes? Far enough and many
don't even turn on lights at night let alone radar!
G

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.

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

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.

That is called blanking and is used to blank out the RADAR as it tries
to sweep through parts of your own boat that may be in the way. If you
have a pole mounted RADAR on the stern, for example, you set it to
blank as it passes the metal mast that is 20 feet away.

Not looking behind you would be a serious error in operation of your
boat. You need to stay aware of all 360 degrees.

wrote in message
...
Not looking behind you would be a serious error in operation of your
boat. You need to stay aware of all 360 degrees.

That was brought home to me many years ago. I was (in UK then) leaving the
Solent by the easterly channel in darkness.
Nice calm night, good visibility, beautiful display of shore lights, so no
problem.
Then I looked behind and to my horror saw a large dark shape with port and
starboard lights both showing with a white masthead light dead centre
between them. In other words a large ship was rapidly overtaking me. I got
out of the channel sharpish and ever since then have never failed to keep an
allround lookout.

Edgar wrote:

wrote in message
...
Not looking behind you would be a serious error in operation of your

boat. You need to stay aware of all 360 degrees.


That was brought home to me many years ago. I was (in UK then) leaving the
Solent by the easterly channel in darkness.
Nice calm night, good visibility, beautiful display of shore lights, so no
problem.
Then I looked behind and to my horror saw a large dark shape with port and
starboard lights both showing with a white masthead light dead centre
between them. In other words a large ship was rapidly overtaking me. I got
out of the channel sharpish and ever since then have never failed to keep an
allround lookout.




That's why I've been more iterested in radar monitors that radar systems
for sailboats. Besides the power drain.



--

Richard

(remove the X to email)

"Edgar" wrote in message
...

wrote in message
...
Not looking behind you would be a serious error in operation of your
boat. You need to stay aware of all 360 degrees.

That was brought home to me many years ago. I was (in UK then) leaving the
Solent by the easterly channel in darkness.
Nice calm night, good visibility, beautiful display of shore lights, so no
problem.
Then I looked behind and to my horror saw a large dark shape with port and
starboard lights both showing with a white masthead light dead centre
between them. In other words a large ship was rapidly overtaking me. I got
out of the channel sharpish and ever since then have never failed to keep
an allround lookout.



Didn't have quite the thrilling experience... we were offshore, sailing
south from SF to Cabo (non-stop delivery), out about 80nm or so. Always kept
a watch and during the day saw a large vessel on the horizon behind us and
closing. Sure, we're stand-on. In any case, we made preparation to remove
the jibe preventer to head up from a broad to beam reach just in case.
Didn't like the idea of playing chicken with a 200m tanker. However, after a
few minutes it was clear that she was changing course to avoid us, so we
held our course. They never answered our hails, but we thanked them anyway.
We were on a 48' ketch.

--
"j" ganz @@
www.sailnow.com

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

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?

A lot depends on sea conditions, the quality of the radar and the
skill/diligence of the watch stander. Seas of 4 to 6 feet are enough
to obscure small boats of all types until they are very close. The
alarm feature is not present on all radars, and even if it exists, may
not be in use. I have a fairly decent Furuno with all of the modern
features and 4 to 6 foot seas generate enough clutter that the alarm
becomes almost useless for spotting smaller boats. More effective are
the electronic signal averaging functions but that requires constant
eyes on the screen and experience/skill interpreting the results.

Not all radar reflectors are equally effective, and they have to be
properly mounted and oriented to be effective at all. The small
tubular units are nearly useless, best are the large round ones hung
in the so called "catch rain" position.

If you are offshore in a small boat assume that you are *not* being
seen, and be prepared to take effective evasive action regardless of
your percieved right-of-way.

SNIP
If you are offshore in a small boat *assume that you are *not* being
seen, and *be prepared to take effective evasive action regardless of
your percieved right-of-way.

Agreed!!

For that matter assume you're invisible anytime you're out, offshore
or for a day sail.

Matt

On 19 Sep 2008 15:30:02 -0500, Dave wrote:

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

Surely the sailboat would give some radar return before the collision
(assuming it is on).

Not at all surely. I recall many occasions on the bridge of a Navy ship when
sailboats were not picked up on radar. And as you know, Navy vessels have
their radar on all the time, and someone monitoring it constantly in CIC.
It's particularly likely the sailboat won't be seen if it doesn't have a
large inboard.

While it may, or may not, apply to western flagged vessels, I have
twice called passing merchant vessels and asked if I was showing a
good return on their radar. In both cases there was a long enough wait
for a response to have allowed them to turn on the radar.

I don't *know* that their sets were off but it certainly appeared so
to me.

Both cases were S.E.A. flagged vessels.

The case in New Zealand of the Korean log carrier running down the
yacht seems to reinforce that premise.



Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)