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Old 03-07-2009, 16:13   #1
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Radar - 18" or 24"

Going to put radar on my boat, and would like others opinions. I have a Garmin 4210 chartplotter now, so will go with their radar also. Am looking at the 18" HD or the 24" HD. Was wondering if others thought the 24" had enough benefits over the 18" to justify the cost difference...Thanks for your input..

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Old 03-07-2009, 16:36   #2
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Originally Posted by bob_77903 View Post
Going to put radar on my boat, and would like others opinions. I have a Garmin 4210 chartplotter now, so will go with their radar also. Am looking at the 18" HD or the 24" HD. Was wondering if others thought the 24" had enough benefits over the 18" to justify the cost difference...Thanks for your input..

What resolution do you need at what distance? That should help bring you to an answer.
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Old 03-07-2009, 17:19   #3
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Bob--

If you have the room for the 24" radome, it will give you measurably better target resolution than the 18" radome--accordingly you'll be able to distinguish targets much more readily. This because the horizontal beam angle is tighter.

FWIW...

s/v HyLyte
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Old 03-07-2009, 22:08   #4
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I have 2 radar systems on my boat. I am a redundancy nut. The larger dome is definitely better at picking out weak or transient targets in fog, rain or steep seas. That is precisely when you want it to work and work well. To me it is “insurance” money well spent.
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Old 04-07-2009, 05:09   #5
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I've got an 18" analog transponder mounted on a 10' pole at the stern. I've never compared it's performance with a 24", but I've also never found myself saying, "I wish I had more resolution". It shows me where the big ships, small yachts, and aids to navigation are. It tracks squalls out to 24 nm. Based on comparing the radar blips with buoy positions on the chartplotter, the range is very accurate, but the lateral discrimination can be off a bit. Closer targets are shown with more accuracy than distant ones, which is a good thing. I would trust it to guide me into harbor through a narrow, marked channel in a dense fog.

I wouldn't be willing to pay more for better accuracy that doesn't give me any more usable information. Plus the additional power consumption, weight, and windage of the 24" could be a consideration.

Here's a question--I don't know if it's answerable. Considering the motion of a transponder mounted, say 40' up the mast of a sailboat in a confused sea state, does a marginal increase in the ability of the 24" transponder to position a target's lateral position really mean anything? In such conditions, the blip will be moving around on the screen due to the erratic motion of the boat, so what's the advantage of some level of additional accuracy?
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Old 04-07-2009, 06:42   #6
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Thanks for the responses...The difference between the Garmin GMR 18 HD and the GMR 24 HD is the 18" has a 5.0 horizontal beam width and the 24" has a 3.6 horizontal beam width...36 mile range vs 48 mile..the 24" weighs 5 pounds more and is about $ 6 - 700 dollars more. The Garmin web site has all the specs.
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Old 04-07-2009, 08:29   #7
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We recently went to a radar seminar put on at West Marine. I went thinking that someone was just going to try to sell us a bigger, and thus more expensive radar unit. As it turned out, the radar people did not try to sell one brand over another, or one size over another. This was simply an informational/educational/operational seminar. We did learn that because radar is line-of-sight, more important than power ratings was the height of the antenna. FWIW, they did say that the more power a unit has, the better target resolution you may have, but there were a lot of variables that could still come into play such as; weather conditions, sea state, reflective abilities of other targets, and of course the individual capabilities of each unit (gain etc... and of course whether the target boat had radar reflectors and where the reflectors were placed on the target boat etc., etc., etc. Additionally, each company competes with others so individual capabilities of different companies may or may not be important in your decision. (I'm a gizmo addict so don't pay any attention to me here in that department)...carrying on....We also learned than there are often individual idiosyncrasies even within same brand of radar unit sot of like personalities, but that's another topic. In the end, what we learned was, that in general, most radar units do about the same thing, and having a bigger more powerful unit will not let you see farther, (although you may have better target resolution with more power but not always...due to all the stuff above). One reason that it's difficult to compare units both in terms of size and quality is the speed of obsolescence. Like chartplotters and computers...what you buy today is outdated almost before you buy it, so arguing about a system that you just bought today becomes rather meaningless tomorrow. Today we have high definition digitized radar, probably in the future they'll be holograms or something we plug into our heads (once they get the bio-physics figured out and a painless installation of course).... But I digress...what I want to add is that I have two radar units mounted on my boat (more by accident more than intention I assure you)...be that as it may...one unit is newer than the other and the newer one is 2000% better than the other but only because it's newer not because it's more powerful or more expensive. (The admiral says I like the new one because it's "prettier and has knobs to play with)...Anyway, they both "see" exactly the same thing...and they both have the same power. The truth is, that because of modernization I am able to buy a more compact, less expensive and more colorful unit with more gizmo's relative, to yesterday's technology. Interesting to compare these two side-by-side. My newer one lets me see better (make that "more funner") with less power consumption than my other 10-year-old-model, but it will not let me see farther unless I can get the dome up higher on the mast, and even then the improved range is not appreciable relative to the cost because of the angle of transmission relative to the curvature of the earth...which is the true limit of all radar units. My slip-mate has a 24" unit, but he doesn't "see" anything any better than my old JRC black and white LED unit...he does see images better, meaning "more crisp or clearly defined" but that may be because the monitor is larger and in color, which has more to do, in this case, with the receiver rather than the transmitter. In my opinion, certainly not $600-$700 better and certainly not $600-$700 better than my other color, HD 18' unit.

As a last safety note...be sure and mount your dome or transmitter higher than any human heads around it especially when they stand up, or move about on deck. One guy mounted his on a pole in the aft of the cockpit...mounted there, it was fine as long as everyone stayed down in the cockpit but the minute anyone went up on deck they we directly in the path of the microwaves radiating out of the transmitter...not a good thing unless your trying to get your brain a tan or want to glow in the dark.
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Old 04-07-2009, 10:10   #8
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True Range...

ixtlan22 you raise a VERY interesting point about the line of sight range...36 and 48 mile ranges mean nothing if the transponder isn't mounted high enough to actually 'see' that far.
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Old 04-07-2009, 10:44   #9
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An important feature to me would be the ability to manually adjust the unit. I'm not sure you can do that now days on all units. You really need to be able to manually adjust things like sea clutter.... otherwise, with a lot of breaking waves or white caps you will be stuck with seeing too much or not seeing the smaller things. The interesting thing about line of sight is that when using radar to track thunder cells etc, you are tracking things at a much higher altitude than your boat, so you can see them a long long ways out. I'm a little with HUD on this one, but 600-700 more isnt too bad in the scheme of thing either. Either will serve you very well.
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Old 04-07-2009, 10:51   #10
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Clutter adjustment

Almost all radars these days have gain controls w/sea clutter and rain clutter manual adjustments.
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Old 04-07-2009, 10:56   #11
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The bigger radar is chosen because of its ability to distinguish between items at close range--not because of 36 vs 24 miles range. Definitely get the bigger unit if it is in your budget. A good source of data is Practical Sailor reprints.
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Old 04-07-2009, 12:04   #12
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The larger of the 2 radar units we have can see small targets nearby in squalls and rough seas significantly better than our smaller unit. When you tune out the rain and the seas you are essentially filtering out weak targets. I am not referring to large ships or tankers at great distances. I mean other sailboats and the like.
A tanker coming straight at you can sometimes be missed in heavy weather as the radar beam bounces out sideways from the bow, it does not return to you. The bridge is low and has a small radar cross section.
I was almost run over by a tanker while lying to a sea anchor in 35 foot seas and heavy rain during Hurricane Ivan just south of Grand Cayman. It did not show up on radar until it was 3 miles away. I was in its direct path. It did not respond to repeated radio calls. It did notice the 25 mm aerial flare that I fired. It immediately turned sideways at a distance of 0.5 Nm. I have never before seen a ship turn so quickly and stop.
Speaking for myself there is no point quibbling over US$700-800. It is insurance for when things go wrong.
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Old 05-07-2009, 00:55   #13
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I was almost run over by a tanker while lying to a sea anchor in 35 foot seas and heavy rain during Hurricane Ivan just south of Grand Cayman. It did not show up on radar until it was 3 miles away.
Oddly enough, this is why I don't think the larger array is worth it. I use radar for weather systems, terrain association when closer to shore and spotting ships.

However, AIS is the primary method I use for ships and I think it works far better.
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Old 05-07-2009, 08:13   #14
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You are right AIS would have been so much better in that situation.
AIS is a great system. One drawback that worries me is it is only required for international voyaging vessels over 300 tons.
I worry about all the local vessels that are not required to carry and maintain AIS.
I like stand alone equipment that couldbe interconnected. The interconnections are not vital for operation of the unit or system. It is solely for the convenience of operation.
I prefer redundancy in all safety related systems. The list is 2 of: Radar, GPS, chart plotter and paper charts, dual steering systems (flip a valve), oversized dual fuel filters. Anything which if it were to fail in bad weather or during a nasty reef entry is only an inconvenience not a crisis.

Like you I use radar mainly to track squalls and weather systems. There are regions where during certain seasons it is impossible to avoid rapidly moving extremely wide swaths of high winds and heavy rain travelling across the surface at over 50 knots. They happen frequently with only a 5-15 minute warning. That is when I want something to assist me to keep track of where things are. We have been caught numerous times in such conditions in the area bordered by San Blass around and up to Cartagena.

It all depends where you plan to sail. That means the local conditions such as weather and access to parts and service.
I hate waiting for parts. Redundancy means I pick when it is convenient for me to find/order and pick up a part not the part telling me what my schedule will be.
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Old 05-07-2009, 11:48   #15
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If you are going to spend a significant time using the radar, get the larger dome. If you are going sail in a fog-free area (like the tropics), and are on a budget, spend the money on something else.
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