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Old 05-03-2015, 10:22 AM   #1
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Radome size

Getting ready to install a new electronics package and have chosen Raymarine. I'm debating between the 18" v 24" HD radome. The size of the 18 dome (which is about 20") works a bit better for my new mounting spot and save about $700.

Both are 4kw so the difference is beam width (3.9 to 4.9) but I'm unsure what that means to coastal cruising in the PNW? What am I giving up with the 18"? Coming from a 1980's Furuno analog so that's my reference point.

Boat is a 42 GB sportfish if that matters.
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Old 05-03-2015, 05:06 PM   #2
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Generally the dimension (18") refers to the antenna element inside not the dome itself. The simple answer to your question is that the wider the array, the better the seperation and detail of targets. In the smaller arrays, you will see targets if they're larger at a greater distance, and smaller ones only closer. As an approximate example, the 60' high interstate bridge will be seen at 10+ miles. The 25' center console might be seen at 5 miles. The smaller floating channel buoys can be seen at 1 mile. It has to do with how much energy you can pinpoint at a target. The wider the array the narrower it can pinpoint and illuminate a target for the same KWs of power.

The other difference is target seperation. With the 5KW 3' open array on my charter boat, I can see a 25' center console fishing next to the seabouy at 2 miles away. With the 18" antenna you won't see 2 separate targets till you're between them.

Nothing wrong with the 18" antenna if you understand it's limitations. With any radar, the only way you get good (comfortable) with it is to run it during the day and learn to interpret what it is and isn't showing you. Mine runs all the time that the boat is moving. As I get older, I see the smaller targets sooner on the radar than with my 20/20 corrected vision.

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Old 05-04-2015, 01:34 AM   #3
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The wider the antenna the better the separation. We have a 24" antenna for our Furuno NavNet. A friend has an 18" antenna on his Furuno and the difference in target clarity and separation is significant. Given the things like rocks, reefs, navaids, small sport fishing boats, crab pot floats, etc. in these waters we would always opt for a wider antenna. To us and based on the difference we've seen an 18" antenna is too limiting in this respect. We'd have gone wider than 24" if the antenna would have fit on our mount.
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Old 05-04-2015, 07:49 AM   #4
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While just about everything can always be "better"....often on recreational boats, adequate is good enough.

For me, going at Trawler speeds and only needing radar a handful of times a year....superior target separation at longer distances isn't really needed. Once you get close, even the smaller radomes give separation.

Being able to correlate targets with charted objects is important. While overlay can be great...it too isn't all that necessary if you can set your electronics up to give you a reasonably clear idea of what is out there.
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Old 05-04-2015, 08:25 AM   #5
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Just for comparison, I have a 12" Lowrance (Koden) dome radar on my CC in NJ. Without a doubt it is the worst performing radar I've ever used or owned. Target separation is poor at best in a harbor. Several boats in an anchorage look like a wall. A rock jetty inlet open to the ocean looks like a dead end canal.
If you usually have fog or rain in your area, go big as you can. You won't regret it.
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Old 05-04-2015, 09:05 AM   #6
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Fwiw that 1 degree beam width equates to a little more than 5 feet at 100 yards or 50 feet at a thousand given the same pulse length etc..


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Old 05-04-2015, 09:12 AM   #7
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In all fairness...radars changed quite a bit with the Raymarine Pathfinder series back 15 years ago.

None of the other smaller, lower power radars came close to their performance because of using different pulses for different ranges.

I would venture to say that all manufactures have caught up now.

I would go with a 24 in, 4 kw dome....digital.....high Def seemed a bit over the top with little actual performance improvement that I could see. Only the smallest of boats really can't handle the 24 in....but if space is an absolute issue....as long as you are an occasional cruiser, 18 in might be adequate in today's newer radar (especially the broadband if you feel that type is for you).
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Old 05-04-2015, 11:35 AM   #8
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Quote:
Originally Posted by psneeld View Post
In all fairness...radars changed quite a bit with the Raymarine Pathfinder series back 15 years ago.

None of the other smaller, lower power radars came close to their performance because of using different pulses for different ranges.

I would venture to say that all manufactures have caught up now.

I would go with a 24 in, 4 kw dome....digital.....high Def seemed a bit over the top with little actual performance improvement that I could see. Only the smallest of boats really can't handle the 24 in....but if space is an absolute issue....as long as you are an occasional cruiser, 18 in might be adequate in today's newer radar (especially the broadband if you feel that type is for you).
I agree. I just installed a 24" HD Dome and love it! It will not disappoint. The one thing I did find out was I am unable to overlay my radar onto the MFD without an electronic compass. I was told the reason was liability. The GPS would keep up with the "go fast" boats and then would hit stuff as the operator was not paying attention to the radar. I just run a split screen and can toggle back and forth with a full screen if needed.

I vote the 24" HD Color.



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Old 05-04-2015, 11:36 AM   #9
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Personally I am more concerned with what is close to me not 10 miles away. I seldom run my radar at greater than the 2 mile range setting, which is adequate for trawler speeds. An 18" dome is fine for those close ranges. If my boat was a go-fast, I would want longer range capability, which would likely mean a larger antenna, although my 18" radome (Lowrance Broadband) has a 2.9 degree beam width, which is better than the 24" Raymarine you are looking at, so maybe I wouldn't need a larger antenna.
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Old 05-04-2015, 12:01 PM   #10
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We generally run our radar at ranges between 0.125 and 3 miles. However even at these short ranges from what we've seen the 24' antenna is superior to an 18" antenna. When it's foggy we boat in the fog and having good clarity and target separation is essential.
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Old 05-04-2015, 12:08 PM   #11
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Add AIS with your radar and you have a great tool in your toolbox......
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Old 05-05-2015, 10:27 AM   #12
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Thanks for all of your feedback. 24" ordered.
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Old 05-05-2015, 12:01 PM   #13
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Lots of close-by targets here of small boats anchored in Richardson Bay, here using a small radome:


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Old 05-05-2015, 01:08 PM   #14
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I'm an open array fan vice the dome. Better lobe separation and target definition. We were coming back from Tacoma Sunday evening and the radar (Raymarine 4kW HD open array) was picking up small fishing boats, buoys, etc., at 3 miles.

That being said, the 24" dome IMO is a much better choice than the 18".
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Old 05-05-2015, 01:44 PM   #15
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In areas with dynamic weather conditions, a longer distance radar capability is an excellent tool for tracking storms. They can move very quickly and be on the unsuspecting mariner before course change or preparations can be made. Also, if you are in a sea lane with large ships, which clip along at 20+ knot speeds, again they can be on you right quick; Not to mention sportfishermen, high performance center consoles, Cigarette style boats et al....you may not be a go-fast but they are!.

The only time we dial down our range is in confined passages like the ICW or Delta sloughs in the fog. For us, radar was the most important piece of electronics along with the depth finders. Followed by the VHF, with the plotter way down in priority. And we don't even like cruising at night.
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Old 05-05-2015, 02:19 PM   #16
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How much range do you need to see what's in front of you? If you want to track storm clouds or a flock of birds OK maybe, but ships and other boats? If your radar is mounted 20' off the water and you are seeing one of the new Triple-E container ships (240' tall), you only need a 24 mile radar. Beyond that, he's out of your effective range according to Furuno.

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Old 05-05-2015, 02:26 PM   #17
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If you think of how few even use their boats away from the dock and then think how many that do travel in conditions where radar is necessary and can use it to 1/2 it's capability......most can get by with the smaller sets that are still decent. Can't disuss them all but many of the newer 18 to 24 dome 4 kw are more than "adequate".

Sure bigger, more power and open array is the ticket.....but overkill for many.
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Old 05-05-2015, 02:58 PM   #18
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How much range do you need to see what's in front of you? If you want to track storm clouds or flocks of birds OK maybe, but ships and other boats? If your radar is mounted 20' off the water and you are seeing one of the new Triple-E container ships (240' tall), you only need a 24 mile radar. Beyond that, he's out of your effective range according to Furuno.

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You are assuming the performance of that 24 mile radar is the same at 24 miles as it is, say at 4. And /or that the 24 mile range unit has the same definition and usability as a larger, higher power unit at that distance or distances even less than that. Having been on a few boats with both a radome and an open array, or comparing my radar to those nearby at anchor with higher or lower power/size, I can tell you, in my strong opinion, that is certainly not the case.

I will say, that the new "broadband" or "high definition" domes are really excellent, especially at close range. If I was only going to be boating in protected waters, I wouldn't mind at all having one as my only unit. In fact that was on my list, to add one in addition to our open array, but that last needed number on the lottery ticket never came up and we survived without it.

Since our boating in recent years has been in areas with a lot of squalls and thunderstorms, yes, we really enjoyed having the long range capability and used it a lot.
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Old 05-05-2015, 03:19 PM   #19
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As with all systems....it depends....

Where do you find yourself 90% of the time?

In the last 8000 or so miles on the ICW, an annual trip to Florida and back....the 4 to 5 times I needed to pick out bad squall lines involving possible tornado action would have been hampered by tall trees lining the ICW.

If the weather is forecast to be really bad, such as I described, I probably won't be venturing into open water..for very long.

So while I agree a more powerful, long range high Def radar is great....just how often does one really expect to use it? On the ICW, money is better spent on a Hotspot for Internet weather as you can see it when your radar wont.

Same with open array or dome. When I get within a 1/2 mile of a target and it finally separates into 2 targets.....at 6.5 knots....it takes almost 5 minutes to get there and in 1/4 mile or less fog, I stil, have plenty of time to check if they both are charted targets or not.

If I were going to run 10 knots plus in 1/4 mile visibility (not smart as a recreational guy)....then all that definition becomes a bigger deal.

Got the money, the room and the cash?...go for it. Travel a lot at night or crappy weather?...go for it

The average guy on TF? Spend your money wisely.
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Old 05-05-2015, 05:27 PM   #20
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How much range do you need to see what's in front of you?
That's a real good point for potential radar purchasers to keep in mind. The requirements for a blue water cruiser are going to be different from the requirements of a coastal cruiser. And in the coastal cruiser category the requirements are going to be different for someone cruising in the maze of islands and channels that make up the PNW, BC, and SE Alaska coasts and (I imagine, having never done it) someone cruising long waterways like the ICW.

Here in the PNW, the straight-line range to an obstacle like an island or the mainland is rarely more than three to five miles other than on the larger bodies of water like the Strait of Georgia, Queen Charlotte Strait, and so on.

Our Furuno NavNet VX2 with a 24" antenna has a theoretical range of 36 miles (IIRC). But what we're really interested in is its sensitivity, return clarity and target separation from 0.125 to 3 miles.

The longest range I can ever recall setting the display to is six miles and that was more to see what it looked like than to actually use it. Sun or fog, we are always running at three miles or less. In the very narrow passes we go though, sometimes in dense fog, we'll be at 0.125, 0.250 or 0.50 so we can see crab trap floats, little sportfish boats, etc.

We would have purchased our NavNet with a 36" antenna if it would have fit on the mount. Not because we care about seeing any farther but for the increased target separation and clarity. But we've found our 24" antenna does fine for us.

Our antenna is also mounted fairly low. Not a problem for us since we don't need to see long distances, and it's an advantage in seeing small things on the water right up to the boat. If we were open water boaters, however or were boating long, straigh-ish waterways where seeing what was coming at us or up behind us while it was still some distance away, a low mount like our would not be beneficial at all.

So, like almost everything else to do with boating, there is no one-size-fits-all solution when it comes to what radar antenna and radar power is best for each boat.
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