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Old 17-10-2020, 19:47   #1
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Dinghy VHF

Planning some cruising next year on the lakes and rivers on and near the border between Minnesota and Ontario. There is no cell phone coverage. Fresh water.



We will have teenage kids, among others, out in a 12' sailing dinghy and a 14' motorboat. We have handheld VHF radios but I am thinking about installing a proper radio with a proper antenna. Extra clutter and weight but better communication.


We have been making do with a handheld VHF in the 26' sailboat but I will be installing an antenna atop the mast and a proper radio before spring.


Wondering what to expect for reliable communications particularly in bays and rivers and other situations where there is intervening terrain. I understand that the basic received wisdom is that VHF is line-of-sight but I know from using it on land that ridge diffraction is a thing and line-of-sight distances can often be exceeded significantly. We would like to be able to count on 10 miles.


I have done some coverage simulations on the ve2dbe website but am not convinced that the models hold up when most of the path is over water.


Would also welcome any installation ideas and practical advice on VHF in smaller boats. Motorboat is aluminum and I'm thinking a 1/4 wave in the middle of the bow decking. Sailing dinghy thinking of an end fed 1/2 wave at the top of the (foam filled) mast with the cable running down the outside.
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Old 18-10-2020, 03:08   #2
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Re: Dinghy VHF

You’re VHF radio horizon will depend upon the heights of the two antennas (send + receive).
Calculator ➥ Radio Line of Sight Calculator for use on VHF/UHF Ham Bands

See also ➥ https://www.cruisersforum.com/forums....html#post1266
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Old 18-10-2020, 03:16   #3
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Re: Dinghy VHF

As long as the communications are between the handhelds and the mothership with masthead antenna, it works surprisingly well, but we only tested this out to 4.25 nm with one high ridge in between.
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Old 18-10-2020, 03:55   #4
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Re: Dinghy VHF

Quote:
Originally Posted by s/v Jedi View Post
As long as the communications are between the handhelds and the mothership with masthead antenna, it works surprisingly well, but we only tested this out to 4.25 nm with one high ridge in between.
However, your (60+ Ft) mast height might be a little higher than that of the OP's 26 Ft sailboat mast.
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Old 18-10-2020, 04:39   #5
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Re: Dinghy VHF

Another great addition to our safety in the dingy is: Garmin Inreach Mini

We always take Garmin Inreach Mini when the dingy rides are longer or we go out on an excursion. we had it once when our outboard died on a long ride and luckily we were able to row back. Our thought was if we couldn't because of the current at least we could use the S.O.S function or send a message with our exact location.
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Old 18-10-2020, 05:13   #6
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Re: Dinghy VHF

"Wondering what to expect for reliable communications particularly in bays and rivers and other situations where there is intervening terrain."

Unfortunately it's a completely empirical question. You won't know the answer until you try it, because the variables involved are too numerous to even list, right down to the quality of your antenna coax and the dampness of intervening foliage. With experience, you'll be able to estimate, or perhaps you can make a pact with the kids "if you can't get us on our every-hour check in, head back to the boat, and always tell us where you are going."
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Old 18-10-2020, 05:17   #7
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Re: Dinghy VHF

Quote:
Originally Posted by GordMay View Post
You’re VHF radio horizon will depend upon the heights of the two antennas (send + receive).
Calculator ➥ Radio Line of Sight Calculator for use on VHF/UHF Ham Bands

See also ➥ https://www.cruisersforum.com/forums....html#post1266

Thanks, Gord. I do know the theory. As your post points out it is straightforward enough on a large body of water where there is no intervening terrain. I will point out that tropospheric scatter, as opposed to tropospheric ducting, is more of a factor in VHF over-the-horizon communications, particularly in areas prone to weather conditions conducive to it.


But on land, or on a mixture of land and water, VHF operates reliably beyond line of site because of ridge effects. I can reliably receive VHF television stations over the air that are 43 miles away from my house despite large intervening hills. And I can transmit and receive to an amateur radio repeater 38 miles away, over the ridge at the edge of a river valley, not line of sight -- and without using antennas or transmitter power significantly greater than what we use on sailboats.


That's hard to characterize mathematically. There are coverage simulations like this one and I've experimented with them but I know they don't always match real world.
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Old 18-10-2020, 05:24   #8
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Re: Dinghy VHF

Quote:
Originally Posted by GordMay View Post
However, your (60+ Ft) mast height might be a little higher than that of the OP's 26 Ft sailboat mast.

I have a 41' mast (height above water) on the larger boat giving a calculated radio horizon of 9 miles, only slightly less than the 11 mile calculated radio horizon for a 65' mast. The sailing dinghy has a mast 16'6" above the water giving a calculated radio horizon of 6 miles. The midpoint of the antenna on the motorboat will be low enough (about 3 feet from the water) that the idea of a radio horizon doesn't really apply since it's already in the first Fresnel zone.
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Old 18-10-2020, 05:32   #9
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Re: Dinghy VHF

Quote:
Originally Posted by tkeithlu View Post
Unfortunately it's a completely empirical question. You won't know the answer until you try it, because the variables involved are too numerous to even list, right down to the quality of your antenna coax and the dampness of intervening foliage. With experience, you'll be able to estimate [...]

Which is why I'm asking about the experience of others so I can make an informed decision on what to try.


For what it's worth, I've never found the dampness of the foliage to be a major factor in VHF. At 800 Mhz it can be a very big deal especially in pine forests where the wet needles are close to a half wavelength long.
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Old 18-10-2020, 06:03   #10
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Re: Dinghy VHF

Quote:
Originally Posted by Jammer View Post
... For what it's worth, I've never found the dampness of the foliage to be a major factor in VHF. At 800 Mhz it can be a very big deal especially in pine forests where the wet needles are close to a half wavelength long.
There's lots of science on the subject.

“STUDY OF PROPAGATION LOSS PREDICTION IN FOREST ENVIRONMENTY.” By S. Meng et al
A comprehensive review of radio wave attenuation in forest environments is presented in this paper...
... The focus of this paper is on the review and summary of the experimental work done in this area and the development of empirical propagation loss prediction models. The propagation loss variation due to external factors such as antenna height-gain, depolarization, humidity effect etc. are examined and discussed individually ...
http://www.jpier.org/PIERB/pierb17/08.09071901.pdf

“Cross-polarization effect of radio waves propagation by forest vegetation in of radio waves propagation by forest vegetation in wireless communication wireless communication systems on transport” by Valentin Popov
https://www.sciencedirect.com/scienc...77050919301309

“Further Investigation into VHF Radio Wave Propagation Loss over Long Forest Channel” by Alade Olusope Michael
https://www.ijareeie.com/upload/janu...ion%20into.pdf
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Old 19-10-2020, 12:47   #11
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Re: Dinghy VHF

Put a masthead antennae on the mothership and put backup whips on the dinghies you replace the rubber duck antennae if you are still having problems.
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Old 19-10-2020, 13:24   #12
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Re: Dinghy VHF

Quote:
Originally Posted by Jammer View Post
Planning some cruising next year on the lakes and rivers on and near the border between Minnesota and Ontario. There is no cell phone coverage. Fresh water.

We will have teenage kids, among others, out in a 12' sailing dinghy and a 14' motorboat. We have handheld VHF radios but I am thinking about installing a proper radio with a proper antenna. Extra clutter and weight but better communication.

We have been making do with a handheld VHF in the 26' sailboat but I will be installing an antenna atop the mast and a proper radio before spring.

Wondering what to expect for reliable communications particularly in bays and rivers and other situations where there is intervening terrain. I understand that the basic received wisdom is that VHF is line-of-sight but I know from using it on land that ridge diffraction is a thing and line-of-sight distances can often be exceeded significantly. We would like to be able to count on 10 miles.

I have done some coverage simulations on the ve2dbe website but am not convinced that the models hold up when most of the path is over water.

Would also welcome any installation ideas and practical advice on VHF in smaller boats. Motorboat is aluminum and I'm thinking a 1/4 wave in the middle of the bow decking. Sailing dinghy thinking of an end fed 1/2 wave at the top of the (foam filled) mast with the cable running down the outside.

You may or may not get 10 miles out of that.


In my experience, 5 miles is pretty reliable. My masthead antenna is 75 feet above sea level. I can't always communicate at 10 miles with the dinghy.
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Old 21-10-2020, 07:13   #13
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Re: Dinghy VHF

Dockhead, what's the VHF installation like in your dinghy? I recall that you have a larger dinghy. Do you have a permanent VHF installation? How high is the antenna? What kind of antenna?
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Old 21-10-2020, 12:19   #14
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Re: Dinghy VHF

Quote:
Originally Posted by Jammer View Post
Dockhead, what's the VHF installation like in your dinghy? I recall that you have a larger dinghy. Do you have a permanent VHF installation? How high is the antenna? What kind of antenna?
Big dinghy was sold. I now have a folding RIB, an Avon 310 Lite. So I use a handheld VHF in the dink, a SH HX870.
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Old 21-10-2020, 14:07   #15
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Re: Dinghy VHF

This doesn't work in your instance as the range is too short, but has interesting possibilities....
https://www.kickstarter.com/projects...municator/faqs
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