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Old 12-17-2007, 05:02 PM   #11
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The all in one units seem great from a compatibility standpoint and you can't beat the ease of installation but, they are very expensive.

This is my setup.



I use the same handheld GPS unit on the boat in the car and hiking/geocaching. The radio, fishfinder and GPS are all connected. This way I can use the GPS for the DSC features on the radio and veiw GPS information on the larger screen of the fish finder.

I think everything together cost me about $650.

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I appreciate the need for a good antenna, but does that count for the GPS unit too?
My portable GPS has a built in antenna that works fine. If you get a fixed mount type you will need a separate antenna for that. They are shaped like a large mushroom. Mounting height is not an issue because the satellites are above the horizon.

I use my fishfinder not for finding fish so much. I use it so I know the depth of the water and the contour of the bottom.


I only ever boat in small lakes and am never more than 2 miles from shoreline. So you may want something better then what I have.
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Old 12-18-2007, 06:32 AM   #12
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Thanks for the pic of your setup. I did see the handheld GPS units and that they can be connected to the VHF.

Question for you - you don't find that the VHF bangs up against your knees or shins the way you have it setup? I haven't spent a whole lot of time in the captain's chair but I didn't notice a whole lot of legroom on my 19'. So if I got the all in one I figured I'd mount it up on the dash.

What I cannot seem to figure out, though, is what is good enough for my "worst case" contingency. The lakes around here are small enough that I'd eventually drift and hit land - and most of them have developments close enough that I could see the lights of nearby homes. That is why I asked about the 20 mile example. Like if I pass out and wake up adrift at sea. How much is reasonably enough? I can't seem to find a way to figure it out, e.g. there is no way that I know of to gauge how many miles or NM any particular unit can transmit.

I did notice the mushroom antenna, so I guess I would need to install that as well as a VHF antenna. But having the depth indicator (fishfinder), VHF and GPS in one is a compelling option. I'm leaning towards spending the extra bucks and buying that "all in one" unit, but I am going to ask around for confirmation that it will be right for my 'worst case' scenario.

Thanks for your help and insight.
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Old 12-18-2007, 02:09 PM   #13
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You can't see it in my picture, but there is a narrow shelf under the helm area that the radio is just above. I also normally just rest one knee on the captains chair while I pilot the boat. This way I am above the windshield and have an unobstructed view of the water ahead.

All fixed mount radios transmit 25watts on their highest setting. So in that regard they are all equal. The number one factor affecting VHF transmitting distance is antenna height. There are no guarantees as to how far the signal will travel.

VHF electromagnetic propagation is known as Line-of-Sight (LOS). Like a flashlight, it can only transmit in straight lines. This differs from lower-frequency radios in the HF range, such as HF-SSB or Citizen’s Band (CB) radio that can rely on "skip" to transmit long distances. For this reason, the transmission range for VHF marine radios is effectively limited by the curvature of the earth and antenna height. In this regard, the higher you can mount your antenna on your boat, the further you will be able to communicate. Of course, this is simply because the line-of-sight for the higher antenna is greater. There is a mathematical formula that can help in determining the line-of-sight distance:




To estimate the communications distance, you must perform this calculation for both the transmitting and receiving boat. Generally you would make the measurement from the top of the antenna to the waterline.


In the above scenario, we can determine the likely communication distances between the two boats, as well as the distant boat and the tower.

The boat with the 12ft antenna, the distance to horizon is approx. 4.2 miles.
The boat with the 18ft antenna, the distance to horizon is approx. 5 miles.
The antenna on the tower, the distance to horizon is approx. 12 miles.
The maximum theoretical distance that the two boats can communicate is 9.2 miles (4.2mi + 5mi)

The maximum theoretical distance the distant boat can communicate with the tower is 17 miles (12mi + 5mi)

It must be noted that this is a theoretical distance due to the line-of-sight limitation. The gain of the antennas will not increase this distance; however, they will make a marginal signal stronger - within the limitation of the line-of-sight distance. In reality, envionmental conditions, such as islands that obstruct the line-of-sight path, weather conditions such as rain or fog, or atmospheric ducting all affect the distance the signal travels.

OK, so you have been on the East side of Lake Michigan, and have heard the USCG from the other side of the lake - more than 80 miles, what gives? There is weather phenomena such as atmospheric ducting that act like a conduit for longer distance communications, but this is not reliable, since it relies on changing weather conditions. And, it is not likely that even though you may hear the transmission, you will be able to engage in a 2-way communication.

(Special thanks to AL C. from BoatingABC for educating the boating world)
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Old 12-20-2007, 05:43 AM   #14
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Wow! Thanks. That answers my question perfectly. Now I understand what is important and why the he handhelds may not be so great (they are only 6 feet off the ground!).

Thanks so much.
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