On Mon, 14 Feb 2005 21:07:37 GMT, Dan Best
wrote:

I dissagree.
The antenna that the energy is radiating off of is much wider than the
mast, so while some of the energy is reflected and scattered, most of it
just flows right on past. The reverse happens with the reflected
energy. As a result, the targets are weaker, but should still be there.
If this were not the case, then whenever you had a mast mounted radar,
everything in a fairly wide cone behind you would be invisible and this
is obviously not the case.

Thanks to you and Otnmbrd for these answers.

On a related topic, make sure that you mount the display where it can be
seen by the helmsman. A friend of mine has it mounted where it can only
be seen at the nav station and having played radar officer calling up
instructions to the helm on a foggy night in SF Bay while dodging
freighters, I'm here to say that that's not how you want to set it up.

It would tend to "compound errors", certainly. I've installed
something on my current boat, however, that I haven't seen before. I
got a gooseneck armature from an old draftsman's flourescent light and
clamped it so that it swings into the companionway. It can be lashed
in position with shock cord, if needed, but usually the friction knobs
do the trick.

On the armature I've secured a handheld GPS on "ship's power" (a 12 V
cigarette lighter style adapter). This means I can reference the GPS
quickly without using my hands, and without it being loose in the
cockpit, without eating batteries (they go through AAs in 2-3 hours of
continuous use), without losing "satellite lock" (because they are on
all the time and in the companionway can "see" enough sky).

Other advantages are (mostly) out of the weather (a ziplock bag will
do the trick here as well).

Of course, I have a tiller, which means I am standing most of the time
by the companionway near the winches and aft of the traveller on the
cabin-top.

I wonder, however, if my "armature idea" would be useful for any
similar devices, as opposed to a "hard-mount" at the wheel? If, for
instance, you had a 15" LCD panel and a wireless mouse, the panel
could be some distance away and still be readable.

R.

On Tue, 15 Feb 2005 04:54:14 GMT, Larry W4CSC wrote:

It's
more like a 2' diameter floodlight shining past the mast, illuminating the
target dead ahead, but probably with some loss of efficiency.
Thanks, Larry. I understand this now.

R.

rhys wrote:

It would tend to "compound errors", certainly. I've installed
something on my current boat, however, that I haven't seen before. I
got a gooseneck armature from an old draftsman's flourescent light and
clamped it so that it swings into the companionway. It can be lashed
in position with shock cord, if needed, but usually the friction knobs
do the trick.

I've seen this type of mount on many boats, though not using the
draftsman's armature. I think the catalogs have brackets intended to
swing out in the companionway.




On the armature I've secured a handheld GPS on "ship's power" (a 12 V
cigarette lighter style adapter). This means I can reference the GPS
quickly without using my hands, and without it being loose in the
cockpit, without eating batteries (they go through AAs in 2-3 hours of
continuous use), without losing "satellite lock" (because they are on
all the time and in the companionway can "see" enough sky).

Other advantages are (mostly) out of the weather (a ziplock bag will
do the trick here as well).

Of course, I have a tiller, which means I am standing most of the time
by the companionway near the winches and aft of the traveller on the
cabin-top.

I wonder, however, if my "armature idea" would be useful for any
similar devices, as opposed to a "hard-mount" at the wheel? If, for
instance, you had a 15" LCD panel and a wireless mouse, the panel
could be some distance away and still be readable.

My current boat, being a catamaran, has a powerboat-like helm station
with the radar mounted on a swinging arm to the side. My previous boat,
had a clever idea that might be of use to some - A hatch was mounted in
the bulkhead in the forward end of the cockpit, and the radar (a large
crt) was mounted on a shelf inside. Its a nice solution for a display
that is too large to mount on an arm. However, once you get used to
have the controls at the helm, its hard to see how you can properly use
a radar that isn't nearby.

On Tue, 15 Feb 2005 04:44:49 GMT, Larry W4CSC wrote:


Isn't it amazing how 2,000 watts of peak RF power just appears from thin
air for only 1-2 watts more DC? Magic? Divine intervention? Maybe its
the printer stepper motor that turns the rubber band that drives the PC
board antenna array...??

Not sure about the merits of this beef.
A radar with a pulse repetition period of 1 millisecond, and a pulse
width of 1 microsecond has a peak power about a thousand times greater
than its mean power - and this is a standard feature of pulse
radars....

Brian Whatcott Altus OK

In article ,
rhys wrote:

On Tue, 15 Feb 2005 04:44:49 GMT, Larry W4CSC wrote:


Furuno? Anyone had water destroy a Furuno radar dome??

OK, crap construction drives me nuts, particularly when it's something
(like a radar) which MUST spend its working life out in the elements.

Assuming the radar itself isn't absolute crap...like that "Mars Bar"
radar the Brits made 25 years ago, say...what is *your* radar of
choice for durability? 'Cause once I go up the mast, I don't want
anything short of a hurricane to cause damage to that radome...

My buddy swears by his old Kodan CRT unit, but he's got a big ketch
and more room and power than most people to play with. The thing is a
toaster-sized box bolted to his coaming, and it takes skill to use it,
but if you can learn that skill, it's accurate as hell.

R.

Give me a Furuno, over any other third and fourth generation Radar OEM
and a Decca over any second generation Radar. First generation radars
were all crap, and the fifth generation is just now coming out, so no one
knows yet who has the best stuff.......

Bruce in alaska
--
add a 2 before @

In article . net,
"otnmbrd" wrote:

I have to wonder how serious a problem this really is.
For instance, if I can run between two buoys spaced 300' with a scanner
that's over 100' in the air and watch them pass down my side, how much
difference can there be with a small boat and a scanner placed 30' up,
unless you are totally crowding the buoy to one side (not good).
Also, by that point, if you lose sight of the buoy, you should have all
ready changed your concentration to some new point or reference, ahead.

otn

OTN, the Horozontal Beamwidth of your Commercial Maritime Radar is
significantly smaller than that of the units found on most Pleasure
type vessels. That makes a HUGH difference in the Target Discrimination
Ability between the two radars. Apples and Oranges, here.......


Bruced in alaska
--
add a 2 before @

I have two singout arms in my hatchway. The raday display is on one and
a gps/fish finder is on the other. Unfortunately, there just wasn't
quite enough room to attach both devices to just one arm, my hatch just
isn't tall enough to have them one above the other. When both are
deployed so the helmsman can see them, it's a little inconvienient since
to in or out of the hatch, you have to either carefully step over them
or swing one of them out of the way. In reality, this is not a big deal
since the radar is only rarely used (but when we do use it, we are
REALLY glad we have it).

Fair winds - Dan Best

rhys wrote:
It would tend to "compound errors", certainly. I've installed
something on my current boat, however, that I haven't seen before. I
got a gooseneck armature from an old draftsman's flourescent light and
clamped it so that it swings into the companionway. It can be lashed
in position with shock cord, if needed, but usually the friction knobs
do the trick.

On the armature I've secured a handheld GPS on "ship's power" (a 12 V
cigarette lighter style adapter). This means I can reference the GPS
quickly without using my hands, and without it being loose in the
cockpit, without eating batteries (they go through AAs in 2-3 hours of
continuous use), without losing "satellite lock" (because they are on
all the time and in the companionway can "see" enough sky).

Other advantages are (mostly) out of the weather (a ziplock bag will
do the trick here as well).

Of course, I have a tiller, which means I am standing most of the time
by the companionway near the winches and aft of the traveller on the
cabin-top.

I wonder, however, if my "armature idea" would be useful for any
similar devices, as opposed to a "hard-mount" at the wheel? If, for
instance, you had a 15" LCD panel and a wireless mouse, the panel
could be some distance away and still be readable.

R.

In article ,
renewontime dot com wrote:

The metal mast and rigging may not obscure your radar display
(an empty "shadow area"), but some of that energy will be bounced right
back and can either cause interference or even damage to your radar's
receiver. All the more reason not to use a 4 kw system.

Nope, not even close to being true. The radar receiver has a Range Gate
built into the frontend that does not enable the receiver to see
anything untill after the transmitted pulse has long since left the
antenna. The Range Gate timing is what sets the Minimum Radar Range
of the radar and is usually set so that the minimum range is on the
order of 50 or 75 yards. Any reflected Transmitter Pulse will have long
since traveled out to the mast or reflective surface aboard the same
vessel and returned long before the Range Gate opened up the receiver
frontend, looking for a return signal.
Your thinking of the Second Generation Radars with RadioActive TR Cells,
that when hear the end of their useful life just opened up and allowed
the Transmitter Pulse to reach the Microwave Diode Crystals, and destroy
them. All third generation and later radars, use a different Range Gate
System, and are not subject to this type of problem. Any return signal
from farther than 75 yards will be so attenuated in power density, that
it can't hurt the receiver frontend. Inverse Square Law prevails in the
RF World. Now the above is all well and good, but does not take in to
account that when rafted up to another vessel which is operating it's
Radar and your radar is operating as well, and the two antenna's point
exactly at each other for a few cycles of their transmitters, that
damage couldn't happen to the recivers from the others transmitter.
the probubility of this is low, but still significant. Never allow
a rafted vessel to operate a radar, when your antenna is pointed toward
theirs.


Bruce in alaska
--
add a 2 before @

In article ,
Jeff Morris wrote:

renewontime dot com wrote:
Thanks for the clarifications, guys. So, to sum up, if you have a
mizzen, it's a great spot for a radar with little downside unless you
think you need the height of the mainmast, but then you may foul an
overlapping genoa.

Does that sum it up?


Just remember that a radar sends out radio waves, and any metal in front
of it will cause part of your radar signal to be bounced back to your
radar. The metal mast and rigging may not obscure your radar display
(an empty "shadow area"), but some of that energy will be bounced right
back and can either cause interference or even damage to your radar's
receiver. All the more reason not to use a 4 kw system.

What??? Are you claiming its dangerous to mount a radar on the mast?
Actually, most masts will reflect the energy away. RayMarine advises to
put a block of wood between the mast and dome if there's interference on
the screen, but I've had several (including a large Nonsuch mast) and
never seen a problem. I don't see how there would be a problem with the
main mast interfering with a mizzen mounted dome.

Naw, don't worry about such stuff, it is not factual information anyway.


Read Meinhert, and Bruce in alaska's posts for the FACTS.......


Me

"Bruce in Alaska" wrote in message news:

OTN, the Horozontal Beamwidth of your Commercial Maritime Radar is
significantly smaller than that of the units found on most Pleasure
type vessels. That makes a HUGH difference in the Target Discrimination
Ability between the two radars. Apples and Oranges, here.......


Bruced in alaska


This I understand. However, and here I need to be careful to note that my
comments are not technical, rather, practical experience based, dating back
to Decca 101's and KH 17's , on multiple size/type vessels ...... I've
rarely experienced a serious problem with close aboard, lost targets that
would negatively impact the navigational procedure I was using, including
docking.
Admittedly, some units were better than others, either due to the basic unit
and/or it's condition and you needed to adjust some procedures, but, my
point is that you don't want to consider a radar's use "drop dead useless"
below a certain range, based on pure technical data, without first checking
your particular unit under real conditions to see if they apply or are
indeed a problem.

MOFWIW

otn