Radar - Dome vs Open Array

[Vincentc]

I trust the open array provides better performance, but I wonder how much. Is it worth the added cost and space?

I have Garmin 4212 and 4012 plotters on a 43 DCFB and would like to add radar. I assume I can just plug in.

It is tempting to just follow the GPS plotter, in bad visibility, and have to remind myself that while it shows where buoys and islands are supposed to be, it does nothing for other boats or uncharted obstructions.

In limited visibilty I am not going to run over 8 kts unless trying to get out of someone's way. While I try to avoid it we do get caught in fog and rainstorms on occasion and do run at night.

I would appreciate the benefit of your comments / advice / experience before I start radar shopping. Not only regarding the question of dome vs open array, but also compatibility with the Garmin system and performance between manufacturers.

Is Garmin the only / best choice for a radar add on in my case or are there other options I should explore?

Thanks for you assistance.
Vincent
43 DC Lilly Marie

[Genesis]

You can only use same-brand designed to work with your existing, unless you want a separate display. If you do, then it matters not but it won't interface.

The dome has materially less SEPARATION of targets. That is, two targets close enough together will appear as one. That is the primary difference. The open has more power (usually) but you're limited by the line-of-sight for targets at ground level (e.g. a boat, marker, etc) anyway.

IF you're interested in using it to spot working birds (fishing) then you need the open (discrimination) AND power.

[Walter P]

Ditto on Genesis' comments.. Additional information is that not only is open array better for seperation, the larger the array the better the seperation. Along with open array, you should be aware that the popular 4KW sets are more than adequite for normal nighttime cruising, be advised that if you intend to be in areas of frequent heavy duty fog or rain, the higher the power the better you will "see" through it. There are of course cost factors in mind, but that's your call as I won't put my hand in someone elses wallet.

Walt
'82 48' Series I MY
Long Branch, NJ

[JLR]

FWIW, I have both a 4KW dome unit and a 6KW open array on my 56 MY. I added the 4KW dome on the brow so that when I remove my radar arch for trips up to Lake Champlain, I have radar. Under normal conditions, I always operate both at the same time. Hence, I can look at both displays simultaneously. To tell you the truth, the difference is marginal at best between the two other than separation. I also have the 6KW unit on my 43 open. It is plenty of power and please also recall that the curvature of the earth is the primary limiting factor in its use for distance. So, if money is the issue, the radome should do the trick. However, it is a Hatteras and the open array is, how shall I say this, more "manly". Just my thoughts.

[REBrueckner]

I agree with the prior posts.

It's the height of your antenna and the size of the target that usualy limits range rather than the power of the antenna array. These 45 foot sportfish boats with six foot long open array antennas at 15 foot height (just for illustration) are ridiculous...but as noted look pretty cool.

A 24" antenna should serve you well, nothing wrong with larger if you don't mind spending more. On my 48 YF, I had a 1989 Raytheon dome antenna on the roof, and added an arch maybe seven feet higher with a 1999 24" open array Furuno...I'd give the slight edge to the Furuno, but maybe that's because it has more intuitive easier to use controls....on rare occasions at anchor when I have compared the two simultaneously, maybe the Furuno would have ever so slightly better detail; underway I 'd never notice it because I'd be navigating via other tools as well...no time to stare and stare.

I opted for black and what rather than color. I am happy with B & W for all my instruments but the color also passes the "looks very cool" test. I don't know what the current price differential is. Others can comment whether it really helps them do a better navigation job.

[sgharford]

I installed full blown Garmin electronic package on my 43DCFB over summer that includes 2x 4212’s and Garmin GMR 21 radar (2 kW 24” dome). Was going to install GMR 24 (4 kW 24” Dome) but was told because of mounting height I wasn’t going to see any big improvement over 2 kW as far as range goes, so I saved some money and power drain and with 2 kW. I love Arrays but couldn’t justify the extra $4k as my intention for use sounds similar to yours (these are not Convertibles).

Piece of advice I can offer – this was Not listed on Garmin Web-site and it took 3 separate occasions with calls to Garmin Phone techs before one figured this out – You may have to update firmware on your 4212 and/or 4010 for it to recognize radar. I purchased everything new over past summer and depth finder as well as satellite radio worked fine, but couldn’t get 4212 to recognize radar. As everything new install I drove myself crazy thinking it was wires. You can get latest firmware updates on Garmin site – for 4212 you need to put download onto SD memory card (camera type) and follow boot instructions (also online).

Also, since you are thinking of doing this, the power and network wires that come with Garmin radars are in a single sheath with warnings not to cut wires. However, if you need to run them thru aluminum tube radar arch you may have to cut. It is OK to cut them down (nothing to do with impendence or resistance), you just have to be aware that one end of network cable (standard RJ45) is type “A” connection, the other is type “B” connection – making this a crossover cable by computer network standards. The Garmin phone tech told me so many people screw this up that they decided to put label on cable warning not to cut.

[JLR]

Just to chime in again, I do not recommend 2Kw units and would stick with 4Kw or up. I have had poor experiences with the former. Also, I just replaced an older color radar with a newer B&W radar. I am old school and to me, the color radar made absolutely no difference whatsoever. In fact, I tuned it to as close to a black and white return (actually green) field as I could get. I would not spend money on color.

[Trojan]

I have all Furuno on the bridge with a color 24" dome. I have no problems with separation. At the lower station I have a black and white (green) 36" Raytheon dome and the Furuno display plus a Garmin GPS.The domes are stacked one on top the other. I like the Furuno better. Size per size there is NO difference in antennas. They work the same and do the same. It would be a trip to mount a 6ft. or 8ft. dome on your bridge.:D . The gear box is large and tall on the open array. Hay it looks cool up there just turning around.:D Radar in a dome, holey-cow, people might think its a TV antenna.:D There goes your ego. In close, size doesn't really matter. With more power the larger the antenna is required to see distance. Bare in mind that radar has a hard time seeing any fiberglass boats. It's the metal objects that show up the best. Floating trees, fishing nets and cork floats seldom show up. At night, I run 3 displays, radar, GPS and depth. And depending on conditions a spotlight. All the electronics are linked together through a hub. Including the lower station. In the lower station it will display all three, but only 2 at a time. The b/w Raytheon is harder to separate and distinguish objects. I would never have anything but a color radar.

Bill

[Vincentc]

Thanks for the excellent comments. You all have addressed my concerns, and then some. ( How did JLR know about my uh-identity concerns?)

I agree, the open array is much more cool and ship like. However I'd rather save the cost spread if the performance difference is not significant, as it relates to my needs

The only feeding birds that have concerned us are the sea gulls that gather when appetizers blow off the aft deck. It does not appear that the ability to discern between two objects close together is that important, since I want to avoid hitting both of them.

Vincent

[JLR]

VincentC- careful about those close objects. Often times, it may be jetties on either side of an inlet or head buoys marking the entrance to the inlet. Needless to say, you need to split those two objects.

[Trojan]

VincentC- careful about those close objects. Often times, it may be jetties on either side of an inlet or head buoys marking the entrance to the inlet. Needless to say, you need to split those two objects.


I don't have this problem with my 24" Furuno. and besides if your in question I look at my GPS. Between the two you should never have any trouble. If your that close you can use your spotlight.

BILL

[OldLimey]

"However, it is a Hatteras and the open array is, how shall I say this, more "manly". Just my thoughts."

I have just installed a Garmin system, including a 24" Dome on our Hatteras. And now I shall have to go and shoot myself!

[Walter P]

There seems to be a lot of confusion regarding power. As I previously stated higher KW is much better for fog and especially for rain. As far as distance is concerned, just about anything can "see" to the horizon in clear weather so distance is not quite as important except----if you want to use your radar for tracking a storm more than 20 miles away. For "punching" through nasty weather there is no substitute for power except more power. Like anything else, size and power does matter in some cases.
Seperation is very important as well. Many times while operating in areas where there are multiple ATONs in close proximity to one another, it sure makes life easy to thread the needle. Cost is usually the limiting factor in making the decision as to which is best for your particular application.

Walt
1982 48 MY
Long Branch, NJ

[Walter P]

There seems to be a lot of confusion regarding power. As I previously stated higher KW is much better for fog and especially for rain. As far as distance is concerned, just about anything can "see" to the horizon in clear weather so distance is not quite as important except----if you want to use your radar for tracking a storm more than 20 miles away. For "punching" through nasty weather there is no substitute for power except more power. Like anything else, size and power does matter in some cases.
Seperation is very important as well. Many times while operating in areas where there are multiple ATONs in close proximity to one another, it sure makes life easy to thread the needle. Cost is usually the limiting factor in making the decision as to which is best for your particular application.

Walt
1982 48 MY
Long Branch, NJ

[Boss Lady]

I have a furano dome on one of my boats. It is great for looking at storm fronts. it is also low to the water since it is on a center console boat. Surface target discrimination sucks. i have not been able to track birds with it. I have a furano open array mounted 23 feet above the water on my Hatteras, you can see birds with it and in the ICW the crab pot buoys look like runway lights on the screen when running at night. If you just want to see big stuff the dome works ok, if you want real radar you need an open array, and 4 kw of power or more.

[Trojan]

I have a furano dome on one of my boats. It is great for looking at storm fronts. it is also low to the water since it is on a center console boat. Surface target discrimination sucks. i have not been able to track birds with it. I have a furano open array mounted 23 feet above the water on my Hatteras, you can see birds with it and in the ICW the crab pot buoys look like runway lights on the screen when running at night. If you just want to see big stuff the dome works ok, if you want real radar you need an open array, and 4 kw of power or more.

As with all antennas, height makes a difference. Low to the water will suck with any radar system. Height makes a difference in separation and discrimination. The beam angle also makes a big difference. Most people don't know what beam angle is. Within 15 miles you can not distinguish a difference in power. More power does not increase the image or improve discrimination. Antenna height will do that in proportion to power. Power will only let you see further. The beam is similar to a flashlight and a search light. Because of the high frequency, distance with radar is a product of power out. Anything 25 miles out that isn't stationary will be gone by the time you get there anyway. Unless your a freighter and high off the water all that power will not increase separation or discrimination. If your looking for airplanes and birds in flight 4 KW will help. All radar is real and the more power you run the more chance there is in getting hurt by the RF beam. A 24inch open array has the same antenna as the 24 inch dome. To me, more power is not worth the money for a pleasure craft.

BILL

[Genesis]

A 4kw open outperforms a 4kw dome because the beamwidth is narrower and the energy (same output) is concentrated into a smaller space. This means it "punches through" better.

However, the 4kw open costs a LOT more.

If you want to spot birds you really want 6kw (or better) on that transmitter. But if you're not using the radar for that - your use is navigation and storm avoidance - then the 4kw domes are more than enough, and the 2kw units are adequate.

The longer the antenna the narrower the beam as it is focused tighter. You COULD put a 4' antenna in a dome, but....

For most cruising use I find the 4kw dome to be a reasonable compromise in that the longer antenna element gives you a significantly tigher beam over the 2kw units. The open looks more "manly", of course.

[Walter P]

With all due respect to all concerned, as I stated earlier the higher KW (power) the better to "blast" through weather conditions including rain, snow and fog. The "antenna" or more correctly - radiator transmits the RF signal through the "horn", which get bounced (reflected) back to the radiator. The larger radiator helps define individual targets and is what gives us the seperation between objects. So the amount of seperation is in direct proportion to the size of the antenna. I believe that essentially is what everyone so far has understood. In order to have your transmitted signal reach out through clutter such as weather, it becomes advantagious to have more power, otherwise you can end up with a "washed out" screen even with the rain clutter adjusted all the way.

Ability to send a clear signal is a function of power, whereas the ability to seperate the reflected RF from the "targets" is a function of the radiator size. Two distinct functions all in one set which is why they have so many sizes and power ranges for the consumer to select. For most of us the ideal set IMO would be a 6 - 10 KW set with a 6 ft radiator. Great power for bad weather with good target seperation.

Walt

[Boss Lady]

Trojan, One of the missing elements in this discussion is target reflectance. The other is the very real differences that the larger (open array) provides in performance for a given input power over the smaller domed array. The narrow beam width of the open array concentrates more radar energy for same amount of input power, and also detects weaker signals better since it also receives better. Most open arrays that recreational boaters use have a beam width of 1.8 to 2.2 degrees, where the dome arrays have 3.9 to 5.2 degree beam widths. This narrower beam width effectively doubles the power density transmitted to the target, and for the dome array to have the same penetration of fog, rain, or to see weak signal targets like birds your dome radar would have to have twice the output power. This still does not resolve the lower resolution for target discrimination.

I had never really used any radar except for open arrays until i bought the Domed Furano unit and saw for myself there are real differences in the performance of the wider beam width. If you ones application is not very demanding then the dome may suffice, but after using what I consider "real" radar the dome is a toy. I was on a friends boat with one of the 18 inch 2.2 kw units and I thought it was broken because there was very little useful information on the screen, although it was still useful for seeing weather and that was about all too.

[Trojan]

Within 10 miles you would not see a difference in units. Just like CBers more power and a bigger antenna is better:D A wast of money for most. I suppose that its manly to run radar in daylight also:D You purchase what you can afford. And if I remember correctly. The " antenna" or more correctly - The enclosed array, does not use a horn. It has as the name states, a phased array, a series of small antennas all phased together and aimed in the same direction. Horns are used on a parabolic dish antennas. All said and done. Power is nice and your not going to place a 7ft Dia dome on the fly bridge. If you feel the need to spend the money and like chasing a flock of birds fifty miles away. Get the big array and a megawatt RF generator. There are times when the bigger array and power will help. Just don't get in its beam when it's operating. Hell It's only money.

BILL

[Vincentc]

I appreciate alll your insights and would like to report my decision.

After pondering it all, price ruled out. I found a Garmin GMR 20 compatible with my Garmin networked plotter for $480, including shipping. It is a discontinued "remanufactured" unit, but from what I can gather it is actually a new unit sold as a closeout, and has a 2 year factory warranty.

It is a 2kw unit and we will see how it performs. While it obviously is not as good as a 4kw open array, it is about 15% of the open array price and less than 50% of a 4kw dome. If anyone else is interested, I found it at getfeetwet.com.
Vincent

[krush]

Nobody has addressed another use of "more power". If your microwave breaks, you might be able to put ur sandwich in front of the radar to warm it up.....

[sgharford]

I bought my GMR21 remanufactured from GetFeetWet too (actually bought all my electronics crap there - worked out well). I originally ordered the GMR24 4kW dome online and the guy actually called me up 15 minutes later and gave me the lesson about mounting height and all that over the phone. Decided remaned GMR21 2kW was right for me after that and switched order (saved about $800). Spent about 1/2 hour with me - not what you would expect from internet based discount marine electronic sales outlet. Not being racist - but he was Indian and really knew his stuff - business must operate out of the twilight zone or something. Where you going to mount it?

[GJH]

Actually, it is very important to run your radar frequently in good weather. That is the only way you will be able to understand what those dots and shapes on the screen are really picking up. Among many other things, that's how I figured out my heading was slightly cocked; stuff straight ahead was shown at 1 o'clock on the radar. When the time came when we had to navigate in extremely dense fog, all that practice sure came in handy. Vincent, make sure you do this after you install your new unit!

We have a Furuno 1944CBB, 6kw 4 foot open array, FYI. We used to charter a boat with a 4kw Raymarine dome unit, and it was fine for poking through the fog on SF Bay and Delta. I am not looking for birds, I am looking for stuff that might sink the boat, so some of the fine points are lost on me, I must admit.

[Genesis]

When I bought Gig it had an open array on it (older Raytheon unit) that crapped after about a year.

I put a 4kw Raymarine dome on in its place.

The dome had BETTER discrimination and sensitivity than the (older) open. Not by a lot, but still....

IMHO the 2kw units are marginal simply due to their antenna size (its small); the longer the antenna, the narrower the beam it throws, and its EFFECTIVE radiated power that counts with ANY transmitter.

Tighter focus (narrower beamwidth) does a LOT more than simply throwing power at the problem. The difference is tremendous - a doubling of power output is only a 3db change in signal, but you can EASILY get that and more from a better (tighter) emission pattern.

Given the choice between a better antenna and more power, I take the better antenna every time. That is where the REAL benefit from the Open comes from - not the RF output power - and is why the 4kw domes are worth considering, as they have a larger (and narrower beamwidth) antenna.

[Vincentc]

My plan is to mount it on the arch (I have yet to build) located aft of the flybridge bimini. My tentative plan is to build an arch modeled after the 43MY out of 3/8 plywood with fiberglass (or a more high tech cloth) and epoxy. I've built a couple of small boats with this system and am comfortable it will look like the aluminum arch, and should not weigh any more. It may take a while but, it will be what I want.

Although the aluminum looks good, I prefer the arch, but in all honesty I have yet to find anything that that looks exactly right, but function trumps asthetics. I do not like the post that holds up the KVH antenna and want to clean up the clutter with an arch for the satellite, GPS, new radar and new TV antenne. As I understand it I have to mount the satellite above the radar to avoid zapping the KVH.

I had a similar experince with the sales person at GFW. He spoke with an accent but what he said made a lot of sense.

Thanks for the reminder regarding practice in good weather. It is all to easy, and dangerous to wait until you really need the radar it to undertake the learning curve.

Regarding bandwith for 2KW vs 4kw domes, the GMR 20 has a 28 inch dome, and the same bandwith as the 4 KW 24 inch GMR 24 according to my research. See below:

Garmin Radar
Inches BandW Kw WattIn Bworld GFW
BMR 18 HD 18 5 4 1200 1670
GMR 24 HD 24 3.6 4 33.5 2000 1700
GMR 404 Ant 48 1.8 4 725 628
GMR 406 Ant 72 1.1 4 1524
Pedestal 2875 2400
GMR 20 Refb 3.6 2 450
GMR 21 3.6 2 936
GMR 24 Ref 4 1254
GMR 18 4 857

(the above date looks different once posted than it does on my spreadsheet. Sorry for the confusion. Put simply, both the GMR 24, 21, and 20 have 3.6 degree bandwith.

Regards,
Vincent

[Genesis]

In that case they are almost certainly using the same patch antenna inside the dome.

For the Ray and Furuno units this is not the case (I've had 'em open and looked.)

[Trojan]

Just for facts. The power out does not determine the beam width. The width of the array determines the beam width. If the open array is the same width as the array inside the dome the beam width will be the same.......The beam width will help in definition.

BILL

[Boatsb]

Just an FYI. An open array is designed to operate in 50+ knot winds and withstand 100 MPH winds. the motors are usually much stronger and the housings too compared with the domes.

[Vincentc]

After reading the information on motor strength and performance in high winds for open array, I looked back at my research.

The GMR 404 (open array) and the GMR 20 (dome) have the same specs here, they are both rated to perform in winds up to 100 kts. On a small yacht in 100 kt winds I wonder whether whether the better choice would be the rosary over the radar.

There are no specs published re motor strength but they indicate that the 404 array alone weighs 12# and its pedestal weighs 42#vs the 20 which weighs 20# total. Thus the 404 package with pedesal has twice the total weight (obviously more substantial.)

Seems to me with the antenna protected by the dome, a less substantial motor should be all you need. Likewise it seems that the dome should better protect the antenna, and unless the dome degrades peformance, for the same antenna size the dome is arguably better.

There seems to be an element of packaging and market perception. To date, my experience with wine, for example, has been more hands on than my experience lately with radar. Screw caps perform significantly better than corks, but few good wines are produced with screw caps, since many people judge a wine by its container.

Vincent

[Trojan]

There is less wind resistance with a dome and requires a substantial smaller motor. No gears, less weight, shorter in height, does the same thing, more water resistance, easier to clean. Birds have more trouble perching on it and it cost substantially less. :D Hell buy what you like. If you want to look more manly. Get the open array. If you want to look more sheik, streamline and have enough money to take the ladies out. Buy the dome. If you want to just look more manly just use a sock or a potato.:D

BILL

[BUSTER]

The last radome I owned was a Rayetheon 4KW R41XX. It was very sharp and reliable,so much so that on a good deal,I replaced it with a 4KW R41XX open array...there wasn't much difference,except there were fewer ghosts with the open array.

My new setup has a 72 mile 4KW Ray Pathfinder open and it is so sharp I have counted the pilings on a bulkhead in the fog and in a big sea I can easily make out the highrises in Palm Beach leaving the West End. The newer stuff is very good in auto-adjust mode.

[thoward]

I will be the odd one on this one, I have a 12kw open on a CC. I run at night and look for birds, I also need to be able to clearly see through rain as I no longer have the comfort of an enclosed bridge to navigate from. The radar runs anytime I leave the dock. I have good seperation and lots of power to see small flocks of birds and surface details to about 6 miles. I know I can't get close to the 72 mile distance because of height. The Hatt had a 4kw open, it could see to the 36 mile limit but did not have the power to pick up small buoys until you were pretty close to them. A 4 kw open would be good for general use. If you run with any speed at night you would need more power. My buddy has a 2kw dome and it picks up boats and such but it is not so great in heavy rain.

It really depends on how you use your boat, a 2kw would work in fair weather fog or night navigation. I would not want to rely on a 2kw during a combination night and rain.

[Walter P]

Todd,

That's what I have been trying to convey. Just about any Radar set made today will work fine for night cruising and/or fog, but in a heavy rain, I'll take more power and a larger open array.

Cost should be the only determining factor here.

Walt