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Old 05-12-2010, 05:06 AM   #1
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Default garmin 18hd vs garmin 24 hd

I have been trying really hard to decide between the 2 units for some time and I'm really torn about which one to purchase since the price between the 2 is about double. At first my goal was to enable me the ability to get out in the dark and see birds. After reading a lot of information about domes vs open array its pretty much an overwhelming vote that domes are really not made to target birds, an open array is just not in my future.

I have read that some guys on the board are able to target birds to a point on the 24 but its still limited to its ability to do so and for the extra 800 bucks I'm not sure if its worth it. The main difference between the 18 and 24 hd units is the beam and from my understanding the narrower the beam the better the target separation. Since I'm not really interested in finding birds anymore and really only concerned about not hitting anything in the water like buoys, boats, and crab pots would the target separation between the two units be that much of an disadvantage that it would merit the idea of purchasing the 24. My biggest use of the unit will be to located crab and lobster pots during the day, will target separation really play a huge factor? I guess my main concern is will target separation really play that big of a deal when the unit is being used for low visibility navigation? Wouldn't a captain drive slower once some thing has been identifies until the hazard has been cleared? How much seperation are we really talking about? Thanks guys
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Old 05-12-2010, 07:52 AM   #2
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God garmin support staff really has no clue. I just got off the phone with some one to ask them my question about what impact will the beam width have between the two units and I was told that its to see further. So I proceed to tell him that both units would be limited to the range do to the height of the antenna....he had no clue what the hell I was talking about. So I asked him what degree of seperation should I see between two objects between the units still had no clue. W
TF
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Old 05-12-2010, 08:05 AM   #3
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I'd highly recommend going with the 24. The extra $800 over the years you'll own the boat will be pennies in the bucket, and will be have much better performance. The 18" domes work, but they are really limited in target def. I've never compared the 2, but I'd bet there is a pretty significant difference between them havign the ability to see small objects like crap pot bouys, plastic bouys... which to mee is very important.
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Old 05-12-2010, 08:45 AM   #4
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There is very limited difference in performance between 18" and 24" domes, the horizontal beam angles of the Garmin domes are repectivly 5.0 and 3.9 degrees. The big jump in performance is between domes and open arrays, Garmin open arrays have horizontal beams in the range 1.1 to 1.8 degrees.
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Old 05-12-2010, 09:53 AM   #5
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5.0 to 3.9 is a 20 to 25% difference.
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Old 05-12-2010, 10:28 AM   #6
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bird,

How did you calculate that difference?
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Old 05-12-2010, 10:32 AM   #7
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Quote:
Originally Posted by tommymo View Post
bird,

How did you calculate that difference?
3.9/5.0 = 0.78

1.00-0.78 = .22

I am assuming he rounded up to 25% from there.
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Old 05-12-2010, 12:53 PM   #8
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Quote:
Originally Posted by tommymo View Post
bird,

How did you calculate that difference?
Simple math calculation as posted above. However, don't be confused, that doesn't mean that the beamwidth difference being 22% different, will translate to exactly a 22% difference in performance. It's nto a 1 to 1 translation, but it is a significant difference, and beamwidth is one of the most important determining specs in radar.

Here's how I would word the difference between the 2 units:

1. If you are pinching pennies, and really just need very basic collision avoidance once in a while when caught in fog, or out at night, the 18 will work just fine. It won't be perfect, and catch all the little bouys all the time, but you will see msot stuff at close range.

2. If you can scrape up a few extra beans, and get the 24, it too will work, but will get more of those small objects, and give a slightly more detailed image.

That is just my opinion, I'm not a radar expert by any stretch. I have had an 18" dome, and it suited me ok. But, my current 24hd is much better, especially with those smaller objects which are a concern to me (I'm in a bay at night with pots and un-lit bouys all over the place).

Would I preferr an open array? You bet ya!! But like you, I didn't want to blow the extra beans, so settled for the array.

Hope that helps....
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Old 05-12-2010, 10:31 PM   #9
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I have an 18" dome on my T-Top, I can see small bouys used for lobster hoopnetting out to about 300 yards, which should be plenty of time to avoid. We have some nasty swells around our islands, 3-6' at 12 seconds, and the fog can appear quite quickly. I have never had an issues with target aquisition or separation for the entire time I have owned the radar. It would be interesting to note the difference between a 24" and an 18" dome though. I would love to have a 24" HD dome but I haven't been able to justify the added cost to myself, let alone the CFO/wife.

I was comming back from Anacapa island in mediocore fog about, 1 mile vis, 3-4' swells when the unit picked up what appeared to be 2 objects connected together but about 300 feet apart. As it turned out, it was a tug towing a yacht and the connection was the line connecting the boats. After that incident, I always cruise with the radar on full screen with data bars for navigation and fuel economy.
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Old 05-13-2010, 02:40 AM   #10
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Quote:
Originally Posted by Birdman View Post
5.0 to 3.9 is a 20 to 25% difference.
And 3.9 to 1.8 is 215% and 3.9 to 1.1 degrees is 350% difference

Conclusion: Difference in performance between domes with same transmit power are minimal, the big difference is between domes and open arrays.
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