Why do we not see open array radar antennas on sailboats?

[The Wolf]

Just too big (3' - 6' sweep)?
Expense?
Power draw too great (wrt dome antennas)?
Marginal benefit not there compared to dome antennas (range, ID of objects)?
Won't fit on mast? May fit on transom pole or transom arch?

[rslifkin]

I'd expect that mounting constraints are 90% of the reason for most sailboats.

[SailingHarmonie]

Originally Posted by The Wolf

Just too big (3' - 6' sweep)?

Not so much, on larger sailboats you can always find space, although 6 feet would be as stretch for almost all.

Originally Posted by The Wolf

Expense?

No, not for all certainly.

Originally Posted by The Wolf

Power draw too great (wrt dome antennas)?

Not this either, not a huge difference with modern broadband rader.

Originally Posted by The Wolf

Marginal benefit not there compared to dome antennas (range, ID of objects)?

Wrong again. I'd love to have the angular resolution and improved sensitivity of a large open array.

Originally Posted by The Wolf

Won't fit on mast? May fit on transom pole or transom arch?

Now you are getting close... Although mounting a large radar down low on an arch or short pole would greatly defeat some of its greatest advantages...

Think about a sailboat... Halyards, topping lifts, sails, It is virtually impossible to mount a large open array and guarantee that you would never tangle it with ANYTHING, EVER. It might be safe in normal operation, but lines do occasionally go astray even on the best managed vessel.

There really is no difference between a dome radar and an open array other than the dome cover. If you could fit a dome over an 3 foot open array, then it would be usable, but then it's not an open array any more, is it?

[Lodesman]

Have you ever seen what happens when a loose halyard wraps around the antenna?

$$$$$

[senormechanico]

I was once on a delivery down the Pacific coast when a line got caught in a three bladed "open array" which was mounted aft on a pole.
Of course, it was blowing pretty good, and it was at night.
The three bladed wind generator didn't want to stop trying to turn as well.
Fun fun fun.

[The Wolf]

Originally Posted by Lodesman

Have you ever seen what happens when a loose halyard wraps around the antenna?

$$$$$

Good case for halyards internal to the mast?

[senormechanico]

In the case I was posting, as far as I remember, it was a topping lift or a head sail sheet gone rogue.

[nuku34]

I had a 36 mile open array unit with a 22" bar on the mizzen mast of my 40ft ketch. It was mounted about 16 ft above the top of the hard dogger. The display was the old raster style with a hood, no electronic ranging, alarms, or chart overlay, but the resolution and detail was incredible.
The scanner bar never caught on anything in 14 years of full-time cruising and we set a mizzen staysail quite often.
Radar is a very useful tool if you practice using it in good weather before you really need to use it.
Radar and the depth sounder are the only electronic nav aids that actually bounce off the hard bits in the real world.

[FlyingScot]

I can't imagine eclosing it in a dome limits it perfromance. It seems the industry has standardized on 18" and 24" dome and anyhting larger 36" 48" 72" are open array. Obviously the bigger the array the better beam width and likely more powerful for greater distances.

I don't see any magic here. You could make a dome for you 6 foot array to prevent entaglement, but do you really want a 6 foot array on your cruising sailboat?

Remember you need to position it higher to get some of that benefit.

[Lodesman]

Originally Posted by The Wolf

Good case for halyards internal to the mast?

You raise your sails inside the mast???

[Jammer]

Originally Posted by The Wolf

Just too big (3' - 6' sweep)?
Expense?
Power draw too great (wrt dome antennas)?
Marginal benefit not there compared to dome antennas (range, ID of objects)?
Won't fit on mast? May fit on transom pole or transom arch?

All of those.


I have radar with a dome antenna mounted on the mast. I use it often.


The benefit of open-array radars over dome radars, and the benefit of larger open-array radars over smaller ones, is not range as such. It is azimuthal resolution, that is, the ability to discern the difference between one object and two objects that are the same distance away and close to each other. That's it. That's all you get. With any radar it's easier to discern whether you're dealing with one or two targets the closer you get to them.


It comes in to play all the time. Boats in the channel next to buoys (which have radar reflectors on them). Groups of boats fishing where you're trying to figure out who's moving and who's stationary. Boats next to the jetty. Positively identifying the presence of a channel and the absence of traffic between two piers or jetties in the fog.



But it matters in proportion to speed. Sailboats are slow. Having stuff blur together on the radar display is a nuisance, yes, throws off the MARPA, but it is still possible to navigate safely at 6 knots. Now, the cabin cruiser guys making 22 knots up on plane, they can't wait until they're half a mile away to figure out that that blob is two boats going in opposite directions up ahead, so they use open array radar.


On a sailboat the best place to put radar is on the mast. You can put it on a stern pole but that will create more windage, more weight aloft, a dead-ish spot in coverage ahead of you because of the shadow of the mast, and reduced range because you'll end up with the radar mounted lower than you would like. Arches are worse than stern poles.



When the radar is mounted on the mast, the genoa will do its level best to wipe it off the mast on every tack. This isn't good for either the genoa or the radar. You want the radar to be small and free of line traps to reduce the damage to the genoa and the radar alike. Open array is right out at that location, you would have to put it on a stern pole or arch.


Power consumption is also a consideration. Open array radars use more power, particularly in windy conditions where the drive motor has to fight to turn the antenna around.


Cost, though a factor, is a lesser consideration IMO. I would pay money for better radar but I'm sure not going to put one of those stern poles on my boat.

[Nicholson58]

Originally Posted by The Wolf

Just too big (3' - 6' sweep)?
Expense?
Power draw too great (wrt dome antennas)?
Marginal benefit not there compared to dome antennas (range, ID of objects)?
Won't fit on mast? May fit on transom pole or transom arch?

There is nowhere I could possibly consider an open array that would not chop up sails or be destroyed by entanglement. We run Gen 4 Broadband. Range and resolution is perfectly fine at 6-10 knots. Mounted on the mizzen.

[gregjm]

Because sails get damaged if they get anywhere near it. Ask me how I know.

[Dockhead]

I've used an open array on a sailboat. It was a Swan 90, however. The antenna was mounted in front of the mast, in a cage.

As others have said, the larger the antenna the narrower the beamwidth and the better the inherent target discrimination. I would love to have an open array radar on my boat.

But a 24" dome modern doppler radar is good enough. Beam sharpening on modern radars helps dramatically with target discrimination.

I've used a B&G 4G radar for about 11 years now and have been pretty satisfied with it. I will be replacing it this year with a 24" HALO radar. I would love a big open array HALO radar but it's too hard to mount it, even on a largish sailboat.

[Mickeyrouse]

I have no interest in open array. The idea of a piece of equipment rotating close to sails, halyards, etc. is too scary. And those are just the things I know about. Too much stuff can get loose at unpredictable moments. The range of a radome is more than adequate.