On Mon, 14 Feb 2005 09:48:35 -0500, rhys wrote:

On Mon, 14 Feb 2005 05:16:13 GMT, Dan Best
wrote:

A common misconception. If you think about it, you will realize that
the radio energy of flowing off of and being received along the entire
width of the antenna which is much wider than your mast. A healthy
percentage of it is reflected back and to the sides, but most of the
energy just flows right on past the mast. It works the same in reverse
for the reflected energy coming back from a target. Thus, the strength
of the reteurn is reduced, but you are still able to see it. Othereise,
all those boats with mast mounted radars would have a fairly wide cone
to their rear where they pick up nothing.

OK, so it's a function of radome width and radar wavelength then. Is
it fair to say that there is a weaker area of coverage dead ahead and
dead astern, then? The masts must absorb SOME of the signal.

I am thinking that a "watch strategy" for using radar under
unfavourable conditions might be to alter course five degrees or so
every three miles (depending on radar range) or so to confirm the
absence of traffic in such "weak spots", if they exist.

My experience in this is limited (obviously), but many years ago I did
use directional antennas for base-station CB radio of all things and
noticed how signal strengths would fluctuate at various points. I
figure radar is similar.

R.

How big is your boat, and in what kinds of waters will your be operating?
My experience with small (39 ft 25,000 lb sailboat) is that your course at
any moment will be off by a lot more than 2 or 3 degrees in any kind of
seaway.

In a bay I might be able to steer a nice straight course. I guess if
"unfavorable conditions" includes calm air and sea with heavy fog, then it
might make sense to snoop around a little with the radar.

But what makes even more sense is to just find out how well the radar can
see straight ahead during good visibility. Then you'll know what you are
dealing with.

Note that I've never used a boat radar, so I can't really comment on the
extent to which it might be blinded by the main mast when mounted on the
mizzen of a ketch.

--Mac

In article et,
"otnmbrd" wrote:

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

Yep, I'll go along with that......


Bruce in alaska
--
add a 2 before @

On Tue, 15 Feb 2005 07:38:34 GMT, "otnmbrd"
wrote:


"Larry W4CSC" wrote in message

Ah, but you have another problem in the fog. The higher the antenna, the
further away the target will disappear as the target approaches the boat!
You won't see the bouy 8 miles away with the antenna down low, but you
WILL
see the bouy in the fog a LOT closer to the boat as you, hopefully, pass
it.

Traveling at Mach 1, I'd understand having more range. But, traveling at
6
knots I'd rather see that target two boatlengths off the port bow with a
lower-down antenna....wouldn't you?

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.

It is a big problem with small-craft radars, in my experience. The
vertical angle is nothing like what you describe on the Furuno and
Raytheon units I have used.
Rodney Myrvaagnes Opionated old geezer

Faith-based economics: It's deja voodoo all over again

Think "watt-seconds".

2000 watts for 2 microseconds requires 4 watt-milliseconds or 0.004
watt-seconds. Throw in the PRF, and the rest is heat.

Roger

http://derbyrm.mystarband.net/default.htm

"Larry W4CSC" wrote in message
...

snip

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...??

On Wed, 16 Feb 2005 03:54:10 GMT, Mac wrote:

How big is your boat, and in what kinds of waters will your be operating?

34 feet fin keel FG cruiser/racer in Lake Ontario. Boat after that
will likely be steel, 40-45 feet, possibly a ketch, operating
offshore.

My experience with small (39 ft 25,000 lb sailboat) is that your course at
any moment will be off by a lot more than 2 or 3 degrees in any kind of
seaway.

Yes. But I can lash a tiller "tamer" in high summer no wind flat lake
conditions and go several minutes without a tracking error by handheld
GPS...if I don't move around much G. Not an issue as I don't have a
radar, but my scenario posits a foggy, still passagemaking at
dawn/dusk on a calm Great Lake...there's substantial ship traffic from
April to November.

In a bay I might be able to steer a nice straight course. I guess if
"unfavorable conditions" includes calm air and sea with heavy fog, then it
might make sense to snoop around a little with the radar.

That's what I thought...twitch starboard and port 5 to 10 degrees
every 10 minutes or so and check your 6 mile ring or something...see
if it stays empty as you've assumed.

I've since been told that this is unnecessary as the mast even on
something like a Nonsuch treetrunk in front of a radar pole won't
block the signal much.

Thanks,
R.

On Tue, 15 Feb 2005 15:59:52 GMT, wrote:

On Tue, 15 Feb 2005 10:20:41 -0500, rhys wrote:

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.

http://www.ram-mount.com/index.htm


Oh, gracious...what a selection! Thanks, BB!

R.

On Tue, 15 Feb 2005 11:34:15 -0500, Jeff Morris
wrote:

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.

As I said, my current boat is tiller-steered, so I am only arm's
length from the mainsheet traveller *forward* of the hatch, never mind
the companionway itself. Reaching for anything and steering involves
using my knees and leaning. If I use the tiller extender, I can go
into the galley and get a refreshing beverage, or lash it in place and
go forward to handle sails. It's not a small boat, either...nearly 34
feet.

Makes me wonder why tillers haven't stayed popular, except that I know
if's because socializing in the cockpit trumps steering.

But that's another topic, perhaps.

R.

On Tue, 15 Feb 2005 20:35:24 GMT, Dan Best
wrote:

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).

Exactly. Would love to see pictures and how you routed the power and
other cables to (presumably) the nav station/DC panel.

R.

"rhys" wrote in message
...
On Tue, 15 Feb 2005 20:35:24 GMT, Dan Best
wrote:

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).

Exactly. Would love to see pictures and how you routed the power and
other cables to (presumably) the nav station/DC panel.

R.

I'm in the process of installing a JRC 2000 radar on my boat. The first
thing I did was install the display. I wanted to be able to see it/operate
it without going below. I'm using 2 horizontal RAM mount arms attached to
one of there vertical mount bases. This is bolted to a small cabinet on the
inside of the bulkhead. I can swing the display out so that I can see it
from the wheel but I don't think I'll be able to see fine detail (don't know
for sure as not fully operational yet). In this position the display blocks
access to below. I can, however swing it to the side so that I can go
forward to look at it and also go below easily. The cables are an issue
I've been wrestling with. The power and NMEA cables are not really a
problem as they are small diameter flexible wire. Easy to route. Its the
display-to-scanner cable that is the problem. Big cable and not that
flexible. I think I may have to disconnect it each time I swing the display
into its storage position inside the boat, against the cabinet. To route
this cable to the stern I'm thinking I will have to glue some white 1"
diameter water pipe to the overhead in the 1/4 berth and feed the cable
through that as I cannot get above the head liner and I need some play in
the cable. When not in use I will have a bracket on the cabinet where I can
store the cable. It will work but its not going to be as neat as I would
like.

Rhys,
No big deal on routing the cables.
The radar (on the port side) has both power and control cables bound
together back into a galley cabinet where they split. The
control/signal cable heads aft through the a large storage volume we
call "the hold" on it's way to the stern mounted radar tower and the
power cable turns inboard into another cabiner behind the ladder where
all out pumps are (pressure water, sump pump out, etc). It is connected
to a fuse block in there.

The gps/fishfinder's power cable snakes under some molding to the DC
distribution panel. It's transducer and GPS antenna cables enter the
pump cabinet where the the swing out arm is mounted. From there, the
transducer cab;e goes down along the side of the engine compartment and
into the bilge where it goes forward to the transducer. The gps antenna
cable goes down into the engine copartment, then aft under the floor of
the hold to the stern, then up throughthe deck at the base of the radar
tower.

Fair winds - Dan

rhys wrote:
On Tue, 15 Feb 2005 20:35:24 GMT, Dan Best
wrote:


I have two swingout arms in my hatchway. The raday display is on one and
a gps/fish finder is on the other.

Exactly. Would love to see pictures and how you routed the power and
other cables to (presumably) the nav station/DC panel.

R.