Scanner height
 

I've just bought a new Raymarine radar in the winter sales (hurray!). Can
anybody advise the correct height to mount the scanner on the mast? My mast
height is about 20m.

Scanner height
 

On Tue, 3 Jan 2006 18:36:26 -0000, "Nicholas Walsh"
wrote:

I've just bought a new Raymarine radar in the winter sales (hurray!). Can
anybody advise the correct height to mount the scanner on the mast? My mast
height is about 20m.

About halfway up seems to be typical, perhaps less in your case since
you have a tall rig. I would try to locate it somewhere above a set
of spreaders to minimize interference with the radiation pattern but
maximize physical support. Minimizing interference with sails is also
important.

Scanner height
 

Wayne.B wrote:
On Tue, 3 Jan 2006 18:36:26 -0000, "Nicholas Walsh"
wrote:


I've just bought a new Raymarine radar in the winter sales (hurray!). Can
anybody advise the correct height to mount the scanner on the mast? My mast
height is about 20m.


About halfway up seems to be typical, perhaps less in your case since
you have a tall rig. I would try to locate it somewhere above a set
of spreaders to minimize interference with the radiation pattern but
maximize physical support. Minimizing interference with sails is also
important.

Ours is about 20 feet up the mizzen on a gimbled platform and we get no
clutter from the mainmast or sails. It is good out to about 15 miles.

Scanner height
 

"Nicholas Walsh" wrote in
:

I've just bought a new Raymarine radar in the winter sales (hurray!).
Can anybody advise the correct height to mount the scanner on the
mast? My mast height is about 20m.



First my condolences. I've just replaced ours on "Lionheart" with the
4TH one in 3 years. The condensation INSIDE the radome just eats the
cheap potmetal the radar receiver box is mounted in, rotting all the
unsealed boards inside with copper-to-potmetal electrolysis. Raymarine
has replaced them free....but is this the way to make radars??

As to mounting it, there's a trade. You are a sailboat so nothing
happens very fast. 15 mile range is overkill at 8 knots as you won't be
there for 2 hours, yet. If you mount it high up, you get excellent
range. Sounds good, eh? Unfortunately, high up also has a tradeoff in
how CLOSE to the boat you can see that big, heavy, CG bouy in the
whiteout fog bank. High up, the radar's beam goes OVER the top of low-
down items, like bouys, and the closer they are, the worse they display.
So, I consider putting the radar antenna DOWN much more important to
safety, where the range is only 4-5 miles, but you can see the bouy 12'
in front of the bow just fine in the fog. About 10' off the water, no
more than 15' up is ideal.

Your cheap Raymarine uses a phased array scanner antenna made out of a
cheap piece of printed circuit board just etched with the antenna
phasing elements and stripline matching sections, all on the board. It
has a quite narrow horizontal beamwidth, but a quite wide vertical
beamwidth, which is great for sailboats because this antenna works well
heeled over to 20 degrees without being leveled by some gimbal
mechanism. We had one on a post mounted on the port corner of the stern
on an Endeavour 35 sloop and I could never see any range difference by
tilting the mount to level the antenna, much. The waves offshore are
what screw up the targets on the other side of them....

AIS is gonna fix all this....soon, I hope. Everyone needs a
transponder!....

http://www.aislive.com/
take a look.

Scanner height
 

This makes almost no sense:
Larry wrote:
"Nicholas Walsh" wrote in
:


As to mounting it, there's a trade. You are a sailboat so nothing
happens very fast. 15 mile range is overkill at 8 knots as you won't be
there for 2 hours, yet.
Of course the RO-RO coming at you at 25 knots gives a closing speed of
33 knots or 3.3 miles every 6 minutes. He'll be on top of you in 15
minutes. Navigating, 15 miles off shore with radar fixes is nice when
your GPS fails.
If you mount it high up, you get excellent
range. Sounds good, eh? Unfortunately, high up also has a tradeoff in
how CLOSE to the boat you can see that big, heavy, CG bouy in the
whiteout fog bank.
Not!
High up, the radar's beam goes OVER the top of low-
down items, like bouys, and the closer they are, the worse they display.
So, I consider putting the radar antenna DOWN much more important to
safety, where the range is only 4-5 miles, but you can see the bouy 12'
in front of the bow just fine in the fog. About 10' off the water, no
more than 15' up is ideal.
So why do ships have theirs up on top of the bridge? Because the radar
is built with fairly wide vertical beams. You won't be able to get it
high enough that you can't see seagulls directly in front of you. In
addition, the pitch of the boat will have a greater negative effect than
putting the radar at the best height you can manage.

Your cheap Raymarine uses a phased array scanner antenna made out of a
cheap piece of printed circuit board just etched with the antenna
phasing elements and stripline matching sections, all on the board.
Not phased array. Check their website
http://www.raymarine.com/raymarine/D...age=4&Parent=2
Phased array scanners are not cheap or common. They are exceptional.
Check it: http://en.wikipedia.org/wiki/Phased_array

It
has a quite narrow horizontal beamwidth, but a quite wide vertical
beamwidth, which is great for sailboats because this antenna works well
heeled over to 20 degrees without being leveled by some gimbal
mechanism.
If it was phased array, none of this would matter but it's not. Look it
up. The horizontal beam is about 5 degrees (for target separation) and
the vertical about 25 degrees (to account for pitching and mounting
height). Nothing to do with rolling.

We had one on a post mounted on the port corner of the stern
on an Endeavour 35 sloop and I could never see any range difference by
tilting the mount to level the antenna, much. The waves offshore are
what screw up the targets on the other side of them....
Hence the need to mount it higher than lower.

AIS is gonna fix all this....soon, I hope. Everyone needs a
transponder!....
And a receiver. But that won't help you spot logs, containers or other
flotsam and jetsam.

http://www.aislive.com/
take a look.

This is generally the worst advice ever. You should do some research
and talk to the guys in the shop.

I would put the dome at a strong point as high on the mast as stability
and common sense would allow. I am not an expert on radar mounting but
I use them daily in my job as a ship's master. I wish I had one on my
own sloop.

Gaz

Scanner height
 

On Tue, 03 Jan 2006 19:00:57 -0500, Larry wrote:

As to mounting it, there's a trade. You are a sailboat so nothing
happens very fast. 15 mile range is overkill at 8 knots as you won't be
there for 2 hours, yet. If you mount it high up, you get excellent
range. Sounds good, eh? Unfortunately, high up also has a tradeoff in
how CLOSE to the boat you can see that big, heavy, CG bouy in the
whiteout fog bank. High up, the radar's beam goes OVER the top of low-
down items, like bouys, and the closer they are, the worse they display.

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

I disagree with this premise based on my own experience. I have a 2
KW Furuno mounted 24 feet above the water. It has absolutely no
problem seeing near by targets, right down to the limitation of the
electronics which is about 50 feet. We were out the other day and it
picked up a duck sitting on the water about 100 feet in front of us.

As far as a sailboat not needing anything past 15 miles because of
slow speed, that is a dangerous assumption. A commercial ship
traveling at a typical offshore speed of 20 kts is moving 1 nautical
mile every 3 minutes. If you are converging from opposite directions
at 8 knots, even faster. I like all the warning time I can get, and
being able to pick up distant shore features is desirable also.

Scanner height
 

Larry,
You brought up a good point, but your reasoning is incorrect. All marine
scanners have a 30 degree verticle radiation pattern, This is too compensate
for roll and heel. So, radiating a target dead in front is not an issue. The
restriction at close range is Pulse width and receiver turn on time. A RADAR
mile is 6.36 micro seconds. If you want to see a target 100 yards in front,
the RADAR set must transmit a pulse and turn on the receiver to catch the
echo in less than .31 micro seconds. That's a very tall order with a
magnetron, as they are not gated. They operate by dumping high voltage on
the cathode, which rings the hell out of the cavity. They turn off when the
cavity decides it no longer is excited and the receiver can not turn on
until there is no more energy being emitted from the magnetron. This is
becoming a very big issue in Europe at the moment. There now is a new
commercial regulation as of Jan. '06 specifically pointed at canal traffic
that stipulates that all new RADAR sets work at 50 meters. For exactly the
reason you mentioned in your post. Now that's tough to do.
Steve

"Larry" wrote in message
...
"Nicholas Walsh" wrote in
:

I've just bought a new Raymarine radar in the winter sales (hurray!).
Can anybody advise the correct height to mount the scanner on the
mast? My mast height is about 20m.



First my condolences. I've just replaced ours on "Lionheart" with the
4TH one in 3 years. The condensation INSIDE the radome just eats the
cheap potmetal the radar receiver box is mounted in, rotting all the
unsealed boards inside with copper-to-potmetal electrolysis. Raymarine
has replaced them free....but is this the way to make radars??

As to mounting it, there's a trade. You are a sailboat so nothing
happens very fast. 15 mile range is overkill at 8 knots as you won't be
there for 2 hours, yet. If you mount it high up, you get excellent
range. Sounds good, eh? Unfortunately, high up also has a tradeoff in
how CLOSE to the boat you can see that big, heavy, CG bouy in the
whiteout fog bank. High up, the radar's beam goes OVER the top of low-
down items, like bouys, and the closer they are, the worse they display.
So, I consider putting the radar antenna DOWN much more important to
safety, where the range is only 4-5 miles, but you can see the bouy 12'
in front of the bow just fine in the fog. About 10' off the water, no
more than 15' up is ideal.

Your cheap Raymarine uses a phased array scanner antenna made out of a
cheap piece of printed circuit board just etched with the antenna
phasing elements and stripline matching sections, all on the board. It
has a quite narrow horizontal beamwidth, but a quite wide vertical
beamwidth, which is great for sailboats because this antenna works well
heeled over to 20 degrees without being leveled by some gimbal
mechanism. We had one on a post mounted on the port corner of the stern
on an Endeavour 35 sloop and I could never see any range difference by
tilting the mount to level the antenna, much. The waves offshore are
what screw up the targets on the other side of them....

AIS is gonna fix all this....soon, I hope. Everyone needs a
transponder!....

http://www.aislive.com/
take a look.

Scanner height
 

Wayne,
50 feet? I don't think so. Check the transmitter specs and do the math.
Lamda = 3.18 u sec per mile, one way.
Steve


"Wayne.B" wrote in message
...
On Tue, 03 Jan 2006 19:00:57 -0500, Larry wrote:

As to mounting it, there's a trade. You are a sailboat so nothing
happens very fast. 15 mile range is overkill at 8 knots as you won't be
there for 2 hours, yet. If you mount it high up, you get excellent
range. Sounds good, eh? Unfortunately, high up also has a tradeoff in
how CLOSE to the boat you can see that big, heavy, CG bouy in the
whiteout fog bank. High up, the radar's beam goes OVER the top of low-
down items, like bouys, and the closer they are, the worse they display.

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

I disagree with this premise based on my own experience. I have a 2
KW Furuno mounted 24 feet above the water. It has absolutely no
problem seeing near by targets, right down to the limitation of the
electronics which is about 50 feet. We were out the other day and it
picked up a duck sitting on the water about 100 feet in front of us.

As far as a sailboat not needing anything past 15 miles because of
slow speed, that is a dangerous assumption. A commercial ship
traveling at a typical offshore speed of 20 kts is moving 1 nautical
mile every 3 minutes. If you are converging from opposite directions
at 8 knots, even faster. I like all the warning time I can get, and
being able to pick up distant shore features is desirable also.

convert Yamaha 9.9 to 15?
 

I was perusing the Yamaha online parts catalog and found the
following:

http://tinyurl.com/an2q6

"All these models use the same part catalog. Be sure to
order only those parts applicable to the desired model.

9.9 MSH (63V5 - Yamaha part code)
15 MSH (63W5 " )

The only difference between the 2 stroke 9.9 and 15 models
that I found was the intake reed valve assembly. They have
different part numbers. Everything else that I checked was
the exact same part number.


Here's the link to the two different parts catalogs (see
"Intake" for the reed valve assembly, one identifed with 63V
and the other with 63W.

http://tinyurl.com/7lpth for the 15 HP

http://tinyurl.com/aaahk for the 9.9 HP


Both have the same carb, pistons, and anything else I could
think of. I have always heard that there is usually little
difference between 9.9 and 15's; 6 & 8's etc. but I was a
little bemused to find that such a simple swap could
potentially save me a lot of cash by buying a 9.9 and a 15's
$41 reed valve assembly. Could it be that simple? There's
about a $400 difference in the retail price by the way.


What I *really* want is a Yamaha 15 ENDURO, but they aren't
found in Canada or the US. If anybody has a line on one in
Mexico or the Bahamas and some suggestions on getting it
into Canada or the US, let me know.

Evan Gatehouse

Scanner height
 

In article ,
"Steve Lusardi" wrote:

All marine scanners have a 30 degree verticle radiation pattern,

Well not quite "ALL"....actually the Furuno Spec is 25 Degrees, and has
been for Years....

Me

Scanner height
 

The Furuno is a fairly inexpensive RADAR and yet according to you, it is
doing
nearly impossible things.

Joe,
You are correct, it does, but it's good if it can. 80 nano sec. is quick.
Many of the commercial sets cannot.
Steve

"Commodore Joe Redcloud" wrote in message
...
On Thu, 5 Jan 2006 06:41:49 +0100, "Steve Lusardi"

wrote:

Larry,
You brought up a good point, but your reasoning is incorrect. All marine
scanners have a 30 degree verticle radiation pattern, This is too
compensate
for roll and heel.

Furuno 1623: Vertical beamwidth 25 degrees (12.5 degrees above and 12.5
degrees
below horizontal)

Furuno 1623: Pulse length .08 ms (short), .3 ms (medium), .8 ms (long)

They operate by dumping high voltage on
the cathode, which rings the hell out of the cavity. They turn off when
the
cavity decides it no longer is excited and the receiver can not turn on
until there is no more energy being emitted from the magnetron. This is
becoming a very big issue in Europe at the moment. There now is a new
commercial regulation as of Jan. '06 specifically pointed at canal traffic
that stipulates that all new RADAR sets work at 50 meters. For exactly the
reason you mentioned in your post. Now that's tough to do.
Steve


Furuno 1623: Minimum range 22m




Commodore Joe Redcloud

Scanner height
 

On Thu, 05 Jan 2006 12:09:53 GMT, Commodore Joe Redcloud
wrote:

Wayne,
50 feet? I don't think so. Check the transmitter specs and do the math.
Lamda = 3.18 u sec per mile, one way.
Steve



Wayne said "about 50 feet". The actual spec is 22 meters. Not that far off for a
casual remark.

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

22 meters sounds about right, about 1 1/2 boat lengths perhaps
although it seems closer then that. I believe Furuno shortens up the
pulse length on the close in ranges to improve resolution.

Scanner height
 

On Thu, 05 Jan 2006 12:05:25 GMT, Commodore Joe Redcloud
wrote:

The Furuno is a fairly inexpensive RADAR and yet according to you, it is doing
nearly impossible things.

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

I'd be happy to demonstrate my Furuno to anyone who wants to see for
themselves. It has significantly better close in range than either
of my older Raytheon units.

Scanner height
 

On Thu, 05 Jan 2006 23:23:21 GMT, Commodore Joe Redcloud
wrote:

I bought Furuno based on the observation that virtually all commercial craft use
them. Lobster boats, Ferrys, USCG...

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

Absolutely right, and those guys use their gear a lot, and are not shy
about discussing its good and bad points.

I'm happy with mine, and everybody who comes aboard and sees the ARPA
functions in action, raves about it.

Even Mrs B, who is not known to get excited over marine electronics,
thinks it's pretty cool (not sure if she knows what it cost). It is
interesting to go up on deck in the middle of the night when it's my
turn on watch and listen to her calmly explain all the boats she
spotted and avoided in the dark.

How much is that worth?

Scanner height
 

"Steve Lusardi" wrote in
:

The
restriction at close range is Pulse width and receiver turn on time. A
RADAR mile is 6.36 micro seconds. If you want to see a target 100
yards in front, the RADAR set must transmit a pulse and turn on the
receiver to catch the echo in less than .31 micro seconds. That's a
very tall order with a magnetron, as they are not gated. They operate
by dumping high voltage on the cathode, which rings the hell out of
the cavity. They turn off when the cavity decides it no longer is
excited and the receiver can not turn on until there is no more energy
being emitted from the magnetron. This is becoming a very big issue in
Europe at the moment. There now is a new commercial regulation as of
Jan. '06 specifically pointed at canal traffic that stipulates that
all new RADAR sets work at 50 meters. For exactly the reason you
mentioned in your post. Now that's tough to do. Steve


Before the water in the dome rots the hell out of the Raymarine radar on
Lionheart, that little sucker can see the 4th boat down our dock on the
1/8 mile range! It even plots the dock correctly from our 20' antenna
on the mizzen. Pulse width must be picoseconds. I don't think it ever
gets very wide to keep resolution high and current drain low. Hell, the
scanner cable to the RL70CRC display where it gets its power from has
very small, long power conductors and most of the power has got to be
heating up the maggie filaments. I had a helluva time explaining to
some captains why a 2KW radar didn't draw more than 2KW off their
batteries. Some of them were afraid to turn 'em on without the engine
charging all that power!...(c;

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

Scanner height
 

Commodore Joe Redcloud wrote in
:

Furuno 1623: Vertical beamwidth 25 degrees (12.5 degrees above and
12.5 degrees below horizontal)



So, if you're heeled over 25 degrees in the big blow, sideways radar
coverage sucks.....I've seen that....

Scanner height
 

Commodore Joe Redcloud wrote in
:

If you are heeled over 25 degrees in a blow, you might consider
shortening sail. You will probably go just as fast or faster, and your
rudder will be more effective.


Commodore Joe Redcloud



You mean the handrail isn't SUPPOSED to be dragging in the water?...(c;

I thought that spray from it wasn't supposed to get me wet at the helm.

Scanner height
 

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?

Scanner height
 

In article ,
Wayne.B wrote:

On Thu, 05 Jan 2006 12:05:25 GMT, Commodore Joe Redcloud
wrote:

The Furuno is a fairly inexpensive RADAR and yet according to you, it is
doing
nearly impossible things.

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

I'd be happy to demonstrate my Furuno to anyone who wants to see for
themselves. It has significantly better close in range than either
of my older Raytheon units.


Ok, I feel a Furuno Story coming on....... Many years ago (1975) I
installed one of the first Furuno KR-124 Radars imported into the
US, on a 85' Yatch in Lake Union, Seattle, Washington. This vessel
had a Professional Skipper & Crew. (ex coastie) Takes about 3 hours
if the antenna, and display are already mounted, and the interconnect
cable is already run but not terminated. Skipper was a sharpeyed older
gent, who wasn't sure that this kid,( myself) knew anything about
"Anything", and was determined to keep an eye on the whole process.
Got everything connected and fired up the radar, to do the Sea Trial,
and get the Heading Flash Reed Switch set to ships head. Nice clear
amazing picture on that analog display. As we were pulling away from the
dock, the skipper looks at the display and asks, "What is all that
clutter, down here in the port quadrant at .25 miles?". I look, and see
a bunch of targets, close together, and then look out with a set of
Binocs, and see a small group of Seagulls sitting on the water. "It is
that group of Gull's over there" says I. He says, "Bull ****". "No",
says I, "Wait till that seaplane taxi's over there, and they all take
flight, and the targets will all disappear of the scope". Sure enough
the Seaplane taxi's right thru the group, and all the targets disappear
from the scope except one. "Look, see they all disapperaed, just like I
said" skipper looks in the scope and says, "Nope, kid there is still one
target there". "Well", says I, "There MUST be something in the water,
over there". Skipper says "Bull ****, I can't see anything there with
these glasses, but we'll just cruise on over and look." So we idle on
over, and sure enough, here is a styrofoam cup floating in the water.
We pick it up, ad set course for the Can, right off GasWorks Park to
use as a Heading Flash setup target, and sure enough when we get .25
Miles from where the cup was, the skipper checks the scope and no more
target. "Hell, that is one great Radar to be able to pick up a strofoam
cup at a quarter mile. Never had that kind of luck with any of my
Raytheon Radars". I just smiled.........

Of course you have to remember that the KR-124 was a true 9Kw radar,
with a real good slotline 3Ft antenna, an excellent Logrythmic
IF Strip, and brand new 1N415E Crystals. When compared to what was
out in the fleet at the time, (Raytheon 1500's,1700's 1900's and Decca
101's and 202's) this was an order of magnitude leap in commercial
radar technology. And it didn't require ANY service for years at a
time, which really made the semi-monthly Raytheon Service look BAD.
That radar and it's follow on KR-248, and KR-448 is what MADE the Furuno
Name in the High Seas Fishing Fleets and North Pacific Coastal Freight
Fleets.

Bruce in alaska
--
add a 2 before @

Scanner height
 

In article ,
Wayne.B wrote:

On Thu, 05 Jan 2006 23:23:21 GMT, Commodore Joe Redcloud
wrote:

I bought Furuno based on the observation that virtually all commercial craft
use
them. Lobster boats, Ferrys, USCG...

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

Absolutely right, and those guys use their gear a lot, and are not shy
about discussing its good and bad points.

I'm happy with mine, and everybody who comes aboard and sees the ARPA
functions in action, raves about it.

Even Mrs B, who is not known to get excited over marine electronics,
thinks it's pretty cool (not sure if she knows what it cost). It is
interesting to go up on deck in the middle of the night when it's my
turn on watch and listen to her calmly explain all the boats she
spotted and avoided in the dark.

How much is that worth?


Priceless, in anyones estimation...........

Me

Scanner height
 

In article ,
"Steve Lusardi" wrote:

The Furuno is a fairly inexpensive RADAR and yet according to you, it is
doing
nearly impossible things.

Joe,
You are correct, it does, but it's good if it can. 80 nano sec. is quick.
Many of the commercial sets cannot.
Steve

80 nanoseconds isn't all that quick, in Xband, with SolidState Receiver
Frontends, Ring Circulators instead of the old T/R Cells of yesteryear,
and SolidState Modulator Strings instead of the old 2E25 Tube modulators
of yesteryear. Third and fourth generation commerical marine radars, have
been doing this good, for at least 20 years. What many "commercial sets"
can't do, is overcome the cheap design tradeoffs that most OEM's have
made to keep their equipment affordable to the guy who only runs his
yatch once or twice a year. If you pay the price for a good marine
radar, you will get the preformance that your looking for. If not
you will get what the Yatch Club Crowd, thinks they should have to pay.
$5kUS buys a reasonable marine radar, and $10KUS buys you what you
really want, but can't justify to the MRS....... Commercial Operators
buy the later........


Bruce in alaska
--
add a 2 before @

Scanner height
 

On Fri, 06 Jan 2006 20:41:10 GMT, Bruce in Alaska
wrote:

Of course you have to remember that the KR-124 was a true 9Kw radar,
with a real good slotline 3Ft antenna, an excellent Logrythmic
IF Strip, and brand new 1N415E Crystals.

Good story. My Furuno is a fairly ordinary consumer grade Navnet
model but we pick up birds all the time on the close in ranges. Not
sure about styrofoam cups but wooden row boats are no problem.

No service required in the first year even though I installed it
myself. We're happy.

Scanner height
 

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.

Scanner height
 

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.

Scanner height
 

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

Scanner height
 

On Fri, 06 Jan 2006 20:41:10 GMT, Bruce in Alaska
wrote:

Ok, I feel a Furuno Story coming on....... Many years ago (1975) I
installed one of the first Furuno KR-124 Radars imported into the
US, on a 85' Yatch in Lake Union, Seattle, Washington. This vessel
had a Professional Skipper & Crew. (ex coastie) Takes about 3 hours
if the antenna, and display are already mounted, and the interconnect
cable is already run but not terminated. Skipper was a sharpeyed older
gent, who wasn't sure that this kid,( myself) knew anything about
"Anything", and was determined to keep an eye on the whole process.
Got everything connected and fired up the radar, to do the Sea Trial,
and get the Heading Flash Reed Switch set to ships head. Nice clear
amazing picture on that analog display. As we were pulling away from the
dock, the skipper looks at the display and asks, "What is all that
clutter, down here in the port quadrant at .25 miles?". I look, and see
a bunch of targets, close together, and then look out with a set of
Binocs, and see a small group of Seagulls sitting on the water. "It is
that group of Gull's over there" says I. He says, "Bull ****". "No",
says I, "Wait till that seaplane taxi's over there, and they all take
flight, and the targets will all disappear of the scope". Sure enough
the Seaplane taxi's right thru the group, and all the targets disappear
from the scope except one. "Look, see they all disapperaed, just like I
said" skipper looks in the scope and says, "Nope, kid there is still one
target there". "Well", says I, "There MUST be something in the water,
over there". Skipper says "Bull ****, I can't see anything there with
these glasses, but we'll just cruise on over and look." So we idle on
over, and sure enough, here is a styrofoam cup floating in the water.
We pick it up, ad set course for the Can, right off GasWorks Park to
use as a Heading Flash setup target, and sure enough when we get .25
Miles from where the cup was, the skipper checks the scope and no more
target. "Hell, that is one great Radar to be able to pick up a strofoam
cup at a quarter mile. Never had that kind of luck with any of my
Raytheon Radars". I just smiled.........

Of course you have to remember that the KR-124 was a true 9Kw radar,
with a real good slotline 3Ft antenna, an excellent Logrythmic
IF Strip, and brand new 1N415E Crystals. When compared to what was
out in the fleet at the time, (Raytheon 1500's,1700's 1900's and Decca
101's and 202's) this was an order of magnitude leap in commercial
radar technology. And it didn't require ANY service for years at a
time, which really made the semi-monthly Raytheon Service look BAD.
That radar and it's follow on KR-248, and KR-448 is what MADE the Furuno
Name in the High Seas Fishing Fleets and North Pacific Coastal Freight
Fleets.

Bruce in alaska


Thanks for sharing that fun story - it must be a rare
bird - a radar story.....

Brian Whatcott Altus OK

Scanner height
 

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

Scanner height
 

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