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17-10-2020, 19:47
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#1
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,848
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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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18-10-2020, 03:16
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#3
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always in motion is the future
Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 18,956
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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.
__________________
“It’s a trap!” - Admiral Ackbar.
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18-10-2020, 03:55
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#4
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Senior Cruiser
Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,362
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Re: Dinghy VHF
Quote:
Originally Posted by s/v Jedi
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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However, your (60+ Ft) mast height might be a little higher than that of the OP's 26 Ft sailboat mast.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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18-10-2020, 04:39
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#5
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Registered User
Join Date: Apr 2017
Posts: 10
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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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18-10-2020, 05:13
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#6
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Moderator
Join Date: Feb 2012
Location: Carrabelle, Florida
Boat: Fiberglas shattering 44' steel trawler
Posts: 6,084
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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."
__________________
Never let anything mechanical know that you are in a hurry.
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18-10-2020, 05:17
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#7
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,848
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Re: Dinghy VHF
Quote:
Originally Posted by GordMay
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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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18-10-2020, 05:24
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#8
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,848
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Re: Dinghy VHF
Quote:
Originally Posted by GordMay
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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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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18-10-2020, 05:32
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#9
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,848
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Re: Dinghy VHF
Quote:
Originally Posted by tkeithlu
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 [...]
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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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18-10-2020, 06:03
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#10
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Senior Cruiser
Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,362
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Re: Dinghy VHF
Quote:
Originally Posted by Jammer
... 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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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
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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19-10-2020, 12:47
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#11
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 20,553
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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.
__________________
Num Me Vexo?
For all of your celestial navigation questions: https://navlist.net/
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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19-10-2020, 13:24
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#12
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,865
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Re: Dinghy VHF
Quote:
Originally Posted by Jammer
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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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.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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21-10-2020, 07:13
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#13
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,848
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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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21-10-2020, 12:19
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#14
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,865
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Re: Dinghy VHF
Quote:
Originally Posted by Jammer
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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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.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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