Radar Pole -- Radar Height

[Dockhead]

I have got a problem or two which can only be solved with some kind of pole on my taffrail, primarily a way to lift the dinghy engine.

At the same time, I covet a more powerful radar to supplement the 4G radar on my mast. The 4G is good for many purposes, but falls down in bearing discrimination and longer range detection.

I wonder if I could use an open array Halo radar on the pole? I guess I could get it 4 or 5 meters above the water surface -- is that high enough?


At the same time, it would be a useful place to mount a few other things, backup VHF antenna, spotlight, GNSS receiver, etc.

[GordMay]

FWIW:
“Installed 15m high, the HALO-4 Radar meets tough IEC 62388 Annex D target detection specifications (excluding beacon and RACON triggering). Installed 3m high, the HALO-4 Radar offers similar target detection performance to our proven Simrad TX06S-1 6kW/4-foot open array pulse radar.”
➥ Simrad HALO-4 Pulse Compression Radar - Simrad Marine Electronics

[Paul L]

You will certainly get much higher resolution with a 1.8* radar over the 5.2* radar. Here's a handy radar horizon calculator Radar Horizon Calculator

[Dockhead]

Originally Posted by Paul L

You will certainly get much higher resolution with a 1.8* radar over the 5.2* radar. Here's a handy radar horizon calculator Radar Horizon Calculator

Thanks. Big hit compared to the 10 meter (33') height of my mast-mounted radar, but I can't put an open array there.

But for land features, storms, and ships, it looks like it could be ok, except (!) in big sea conditions.

Hmmmm

[Paul L]

You could save yourself some money and put s 24in 4kw closed array on the mast and move the 4g to the pole. 24in radar will have approx. 3.9* res.

[Dockhead]

Originally Posted by Paul L

You could save yourself some money and put s 24in 4kw closed array on the mast and move the 4g to the pole. 24in radar will have approx. 3.9* res.

I've had the 4kW dome, and the bearing resolution is even worse than that of the 4G continuous wave radar.

Sent from my D6633 using Cruisers Sailing Forum mobile app

[Paul L]

Originally Posted by Dockhead

I've had the 4kW dome, and the bearing resolution is even worse than that of the 4G continuous wave radar.

Sent from my D6633 using Cruisers Sailing Forum mobile app

19in or 24in? That is the important issue. The power just gets you a little more punch, like through storms. The array diameter determines the horizontal resolution.

[Dockhead]

Originally Posted by Paul L

19in or 24in? That is the important issue. The power just gets you a little more punch, like through storms. The array diameter determines the horizontal resolution.

It was a 24" Pathfinder radar, and it was a good radar, with a number of limitations, however. It was not really better at anything than my 4G radar, except seeing weather at longer distances. The bearing resolution was not noticeably better (the signal processing in the 4G radar makes up partially for the smaller antenna).

I don't think we can expect decent bearing resolution with antenna less than about 4' or 5'. The HALO radar looks really intriguing because it -- allegedly -- has signal processing on par with the 4G radar.

Not sure I can afford the windage, however It's a pretty bulky unit.

[Pelagic]

I can understand the desire for a larger more powerful open array scanner as the discrimination @ 12nm range is some much better as is the ability to tune out clutter manually.

However, height and placement are such key factors, that I think you would be disappointed with the final performance

Also consider that a good AIS masthead antenna will give you that critical long range target info for Ship detection .

So perhaps look at improving the AIS display side if needed may be a better option when crossing the channel.

[Dockhead]

Originally Posted by Pelagic

I can understand the desire for a larger more powerful open array scanner as the discrimination @ 12nm range is some much better as is the ability to tune out clutter manually.

However, height and placement are such key factors, that I think you would be disappointed with the final performance

Also consider that a good AIS masthead antenna will give you that critical long range target info for Ship detection .

So perhaps look at improving the AIS display side if needed may be a better option when crossing the channel.

My AIS system works perfectly, so dealing with ship is a small part of what I use radar for. I use OpenCPN for complex collision avoidance with AIS. The only thing I would improve would be to go to a Class "A" system, which I will do in my next boat for sure.

I use radar for the following:

1. Enhancing visual watchkeeping at night and in bad viz.

2. Enhancing offshore watchkeeping with guard zones.

3. Navigation.

4. Collision avoidance with vessels not broadcasting AIS (mostly pleasure vessels, but fishing vessels at night are a real menace if you can't detect and avoid them).

5. Gauging distance to uncharted objects (other boats in an anchorage, etc.)

6. Detecting and gauging distance to channel markers, fishing pots, etc.

7. Keeping track of squalls and approaching weather events.


So the 4G radar excels at 1, 2 and 3 and is pretty good at 5 and 6.

It is somewhat usable for 3, 4 and 7, but lacks bearing discrimination to do 3 and 4 well. MARPA is almost completely useless.

A powerful open array radar would eliminate all the gaps.

I used a big Northstar open array on a 90' yacht I spent some time on a decade ago, and it was awesome. I wish I could have something like that on my boat, but I recognize this is probably a pipe dream.



For all its faults, the 4G radar does have one absolutely killer quality -- the signal processing is so good, that there are practically zero false alarms when using the guard zones. This makes them from something fairly useless on my old Pathfinder radar to a killer enhancement to watchkeeping, even in daylight, when offshore. This radar would be worth having alone for this quality.

[Paul L]

Originally Posted by Dockhead

It was a 24" Pathfinder radar, and it was a good radar, with a number of limitations, however. It was not really better at ......

My old Ray Pathfinder radar was not a very good radar. Certainly no comparison with my current Furuno.
The larger antenna of the open array unit is going to trump (non-political) any of the small units.

[S/V Alchemy]

Originally Posted by Paul L

You could save yourself some money and put s 24in 4kw closed array on the mast and move the 4g to the pole. 24in radar will have approx. 3.9* res.

Yes, this is what I was thinking. I asked a radar tech a few years ago what was the best choice for offshore. He said "Pulse radar (old-style) closed array on the mast for distance and spotting squall lines, ships, cliffs beyond the height of eye, etc.) and digital radar on a pole to spot docks, buoys and half-awash containers a mile off". Basically, digital's great for coastal, near-horizon (10 NM or less) stuff and has "finer grain", but an intermittent 4 KW as high as is practical will buy you five more minutes of deck prep when that squall is still 32 NM away.

I found his arguments nuanced and persuasive, unlike radar sellers' marketing bumf.

[Dockhead]

Originally Posted by S/V Alchemy

Yes, this is what I was thinking. I asked a radar tech a few years ago what was the best choice for offshore. He said "Pulse radar (old-style) closed array on the mast for distance and spotting squall lines, ships, cliffs beyond the height of eye, etc.) and digital radar on a pole to spot docks, buoys and half-awash containers a mile off". Basically, digital's great for coastal, near-horizon (10 NM or less) stuff and has "finer grain", but an intermittent 4 KW as high as is practical will buy you five more minutes of deck prep when that squall is still 32 NM away.

I found his arguments nuanced and persuasive, unlike radar sellers' marketing bumf.

Maybe, but I'm not convinced that a 24" pulse radar is going to do anything all that much better than my 4G radar.

The early digital radars were quite limited in range, but the 4g is not so bad compared to the pulse radars I've used. I can see ships out to maybe 20 miles, and weather and tall buildings or land features out quite a bit further than that. Another question is definition at those ranges, which of course is poor.

[tkeithlu]

What's missing in this discussion is the horizon. The formula for distance to the horizon in miles for height of the antenna (or your eye) in feet is 1.22 times the square root of the height. For a radar antenna ten feet above the water, that's 3.9 miles. To first see an object over the horizon that itself is ten feet tall, you do it twice and get 7.8 miles. The best radar in the world is not going to give you more range than its height allows. That's why you can sneak under the radar in an airplane, and the DEA used to (maybe they still do) put their Gulf coast radar in a tethered balloon.

[Dockhead]

Originally Posted by tkeithlu

What's missing in this discussion is the horizon. The formula for distance to the horizon in miles for height of the antenna (or your eye) in feet is 1.22 times the square root of the height. For a radar antenna ten feet above the water, that's 3.9 miles. To first see an object over the horizon that itself is ten feet tall, you do it twice and get 7.8 miles. The best radar in the world is not going to give you more range than its height allows. That's why you can sneak under the radar in an airplane, and the DEA used to (maybe they still do) put their Gulf coast radar in a tethered balloon.

I think those of us who have used radar for a few years are pretty familiar with this effect


Since most of us are not involved in hunting for drug semi-submersibles, there's nothing only 10 feet high which we need to see from all that far away.


One thing I would be concerned about with radar only 10 feet above the water is sea state. Sea clutter is a bigger problem -- as far as I understand -- when the radar is lower down. Also, I sail in waves bigger than 10 feet on a regular basis, and would not want to be deprived of my radar.

My current radar is 10 meters or 33 feet above the water.