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Old 20-02-2007, 16:14   #1
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Help with projects needed - first the radar

There are some improvements I've been dreaming of for some time now and this year it all seems to be coming together. But I need help.
First the radar.

Maybe I should have asked for help earlier?
But I went ahead and bought it.
It is the JRC 1000 MkII.
It only has a range of 16 miles but that means it is not so expensive to buy and it is not such a big drain on the battery.

Anyone using it? Loving it? Hating it?

Anyway there are two parts to a radar. The scanner (aerial) and the screen/control unit.

Now I have the bits and they are sitting in their cardboard box in the salon.
The question is what do I do with them.

Where should the scanner go and where should the screen go?

The screen can go inside by the chart table or outside by the helmsman. As I sail alone a lot of the time having the radar inside is not much use. So it has to go outside.

The alternatives I can think of for the scanner are
1) the mast
2) A sort of arch aft over the bimini [to be built]

This is where I need some creative thinking.

If the scanner goes up the mast it has to be high because there is the spinnaker pole resting to the front of the mast up to the fiirst cross trees about 5 meters up. That only leaves about 10 meters of cable to get to the screen. But the yacht is over 12 m long and the total cable length is 15 metres.

Considering all the turns the 15 metres may not be enough for the screen to go in the cockpit.

Is it OK to extend this cable or would I be damned for ever if I attempt it?

The alternative is to mount the scanner to one side of the mast but I wonder why I never saw one like that. Is there a good reason or just the natural tendency for symmetry plus the inevitable large blind area to one side?
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Old 20-02-2007, 16:39   #2
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While it can be done, I don’t recommend DIY splices on RADAR Cables.

From the JRC (America) Website: RADAR 1000MKII 6.5" Black & White LCD

Antenna Cable Accessories
33’ (10m) Antenna cable #CFQ-8571-1033'
49.5' (15m) Antenna cable #CFQ-8768-15
66' (20m) Antenna cable #CFQ-8768-20
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Old 20-02-2007, 17:10   #3
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I agree Gord which is why I posed the question. Hard reality says that with both ends of the cable being too fat to pass through a cable conduit / hole there has to be some cutting and splicing.

And if she ends up on the mast the mast has to come down...
This is a puzzle I could do without.

I wish there was a trained Japanese technician in the box.
I would treat him to some nice Greek food. Honest!
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Old 20-02-2007, 17:18   #4
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I'm certainly no expert, but...

I believe that having radar is kinda like having someone with extra sharp eyes on watch with you at all times and and can answer questions when your tireed eyes are playing tricks on you. They're also valuable in helping you track steer around rain squalls and (needless to mention) collision avoidance.

I believe the two biggest criteria concerning the mounting location of the transmitter (dome) are Safety & Performance and one should mount the transmitter at least two ft above the head of the tallest crew member... and mount it so that it is not directly level with a horizontal structure such as the boom or coach roof.

I believe the best arrangement would be to have two diaplays - one at the nav station and one within view of the helm. And if I had to choose one or the other - I'd prefer to have the display within sight of the helm.

On my last boat - I installed a 16 mile Furuno unit with the dome located above the spreaders and the wire was simply clamped down the mast externally. I included a longer cable at the time of purchase and West Marine was kind enough to give me a refund for the un-used cable upon return after the installation was completed. I routed the cable through the deck with a 3/4 inch hole I drilled at the base of the mast and routed to the display mounted at the inside helm of our pilothouse. The display was highly visable from the aft helm and spent most of the time in open ocean on a six mile range with a guard zone set up between two & four miles.

This time... I plan to spend a little more dough and install the dome on the aft part of our stern arch and mount the main display at the nav station AND a repeater display in the cockpit.

In closing (and I'm sure others will disagree) I believe a 16 mile radar range is all that's needed on a blue water cruising vessel. I believe a CRT display offers a better immage but an LCD display saves space. And I believe that transmitter leveling devices are a waste of good money.

Again - I'm certainly no expert... but that's my opinion on radar.

Kirk
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Old 20-02-2007, 17:22   #5
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Skipperaris - I mounted mine on the mizzen but have seen alot on a pole at the stern quarter supported by the stern rail with the cable running inside the pole. You can cut the cable and junction it using a multi electrical lead connector panel but it must be inside and dry and away from electromagnetic influence. You can get the pole up about 10 feet off the deck by using a 1 1/2" diameter pole with a heavier wall thickness.

This arrangement will make it easy to service. As for the display, mine is at the helm.

Good luck.
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Old 20-02-2007, 17:28   #6
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Take a look at the Blue Sea Systems “Cable Clam”:
Blue Sea - CableClams - Engineers of marine electrical equipment
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Old 20-02-2007, 17:31   #7
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BTW - if you don't run the cable through the pole base through the deck, there is a waterproof through deck product called Sea Clam? - I think which comes in a size large enough to accomodate the plug end of the cable. With it you can remove the cable from the inside of the boat altogether if needed without having to cut the cable
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Old 20-02-2007, 17:32   #8
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Great minds think alike Gord - but yours has a better memory
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Old 20-02-2007, 18:00   #9
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You were lucky to have a pilot house, Gallivanters. I simply haven't got one.
Also the main reason I wanted a radar was fog. I have had some close encounters...

It does not happen a lot but when it does you cannot see anything, not even the pointy end.

About the height of the dome I'm guided by the info in the makers' book of words which specifies the beam width in a vertical sense as 30 degrees.

This means to me that the radome must be able to see an unobstructed 15 degrees below the horizon. With the yacht being about a nominal 12 metres long, the height of the dome is 3.2 meters. I find that excesive for a pole to be sticking up although it is not exactly prohibitive.

On the other hand the technical guy told me that the radome is an aerial and aerials are better off if they are higher up.

I could not argue with that.

I have seen radomes such as you describe on a pole at the stern, here at the boatyard, Benny but I have my doubts. They certainly look ungainly.

But I have not burnt my boats yet. I am designing an arch to go over the bimini for the solar collectors, wind generator, GPS aerial, stern light and a strong spot light that is currently standing at 2 meters above deck level on paper. It would not be unrealistic to strap a 3.5 meter pole to this and over the stern platform which is also still on paper. It would surely make cabling easier.

What is this multi electrical lead connector panel Benny?

Anyway please keep on pouring it in. I'm soaking it up. THANKS!
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Old 20-02-2007, 18:14   #10
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Thanks Gord and Benny. If you were your sister(s) you would be getting a big kiss.

That cable clam should do it!
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Old 20-02-2007, 18:38   #11
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Quote:
Originally Posted by skipperaris
Where should the scanner go and where should the screen go?

The screen can go inside by the chart table or outside by the helmsman. As I sail alone a lot of the time having the radar inside is not much use. So it has to go outside.
I have it both ways aboard Raven. My display is mounted on a swinging mount fixed to the bulkhead above the nav station. When I want it visible from the helm, I swing it out into the companionway. For me, it's been a great solution.



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Old 20-02-2007, 19:01   #12
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Quote:
Originally Posted by skipperaris
This means to me that the radome must be able to see an unobstructed 15 degrees below the horizon. With the yacht being about a nominal 12 metres long, the height of the dome is 3.2 meters. I find that excesive for a pole to be sticking up although it is not exactly prohibitive.
Not exactly -- that is just a description of where the antenna can see. You can imagine the beam coming out of the antenna as being a 30 degree angle, 15 degrees above and below horizontal, assuming your boat is horizontal at the time.

If you heel over 20 degrees, your radar will be looking down at the water on one side and up at the sky on the other side. On the "looking down" side, your range is reduced. It is like pointing a flashlight at the ground -- you only see what is in the beam, and things further away are not illuminated. On the "looking up" side, it is like shining your flashlight up in the air. You might see a bird flying over, but not the rock you are about to step on.

If you only heel over 10 degrees, you have the same effect, but less so. On the "looking up" side, at least some of the beam falls on the water.

The edge of the beam is not really sharp like a flashlight -- as the angle gets further from the center, the antenna is gradually less effective. Still, this is a good enough analogy for now.

Quote:
On the other hand the technical guy told me that the radome is an aerial and aerials are better off if they are higher up.
Higher is not necessarily better for a radar. Yes, if the radar is too low, it has a closer horizon. But...

If your radar is too high, things that are close-in can get under the beam where you can't see them. That is not good.

By putting the antenna higher, you move the horizon further away, but there is no benefit to having a horizon that is more distant than the range of the radar. In other words, your radar will not see an object 32 miles away, no matter how high it is. It is only a 16 mile radar, so there is no need to mount it any higher than necessary to get a 16 mile horizon.

You can use the beam width and angle of heel to calculate a cone around your boat that the radar can't see. (Actually, there are two -- one below the radar and one above it.)

Quote:
I have seen radomes such as you describe on a pole at the stern, here at the boatyard, Benny but I have my doubts. They certainly look ungainly.
My radar is on one of these. It is a 24 nm radar that is 12 feet (a little under 4 meters) or so above the water. That was my compromise between too high, too low, too expensive (for the pole), too hard to route the cable, keeping the crew out of the beam, etc.

Quote:
But I have not burnt my boats yet. I am designing an arch to go over the bimini for the solar collectors, wind generator, GPS aerial, stern light and a strong spot light that is currently standing at 2 meters above deck level on paper. It would not be unrealistic to strap a 3.5 meter pole to this and over the stern platform which is also still on paper. It would surely make cabling easier.
I would have done this if I was going to have an arch anyway. I found that the radar pole was cheaper than an arch, and I didn't need the arch for other purposes.

If you decide 3.5 meters is the right height, remember that it is height above the water that is important, not above the arch. If the arch is 2 meters high (so you can walk under it) and is on deck 1 meter above the water, you can consider putting the radar 0.5 meters above the top of the arch. Just make sure it is high enough that the crew aren't in the beam. (The manual will tell you minimum ranges and such.)
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Old 20-02-2007, 21:16   #13
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Stop your boat 16 miles from a shoreline mark and climb your mast until you can just see the mark. This should be the height of your scanner. If you reduce your close in detection to less than 1 mile at sea level that is not a problem as any targets within this range (except for buoys) will generally be tall enough to appear in the scanner beam. Radar use in fog is all about detecting targets as early as possible and tracking them, relying on it to dodge around close in targets is a recipe for disaster. Attending a radar course will be invaluable, too many sailors have the toys but are unaware on how to make the most of the dollars they have spent.
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Old 20-02-2007, 21:56   #14
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"But I have not burnt my boats yet. I am designing an arch to go over the bimini for the solar collectors, wind generator, GPS aerial, stern light and a strong spot light that is currently standing at 2 meters above deck level on paper. It would not be unrealistic to strap a 3.5 meter pole to this and over the stern platform which is also still on paper. It would surely make cabling easier."

Whatever you do, don't mount anything above your solar panels.
While we were cruising, we saw that all the time! It makes as much sense as painting your dodger windows black!

Your radar will work just fine for what you want as long as it's high enough so you don't run into it. Add enough so you aren't standing in the beam while it operates.

Steve B.
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Old 20-02-2007, 23:36   #15
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Thank you Raven. Your setup looks really neat. Unfortunatelly my nav station is not visible from the helm even if my own vision was better. Which it ain't.

Thank you Coot I'm not any nearer to making a decision but I feel a lot more informed.

My point about the 15 degrees was that the radar beam is not "wasted" scanning my deck which would be the case regardless of heel if the radome is low down.
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