VHF Chanel

[seeker242]

IWhat most radios have is a dual watch facility, where the radio is set to the working channel you use and flicks back to ch 16 then back again. When a signal is received on ch16 the radio will stay on 16 until the signal stops.

But generally is not automatic. The dual watch function has to be manually enabled.

 

[Snoweman]

They must monitor a common channel to hear any directives from the harbor master. My last dive was cancelled by a sudden port closure. I don't speak Spanish, but I heard it loud and clear over the radio.

 

[Tug]

Like @seeker242 said, the dual watch function needs to be manually set and not all radios have this functionality.

 

[Christi]

In Cozumel, the emergency channel is Channel 6

True, the international distress channel is 16, but if you call Channel 6 in Cozumel, your call will be heard because that is the main channel used here. The Harbor Master also uses Channel 6 to make announcements.

 

[MargaritaMike]

In Cozumel, the emergency channel is Channel 6

True, the international distress channel is 16, but if you call Channel 6 in Cozumel, your call will be heard because that is the main channel used here. The Harbor Master also uses Channel 6 to make announcements.

This is good information. Thank you, Christi. My concern now becomes the people who are indoctrinated that Channel 16 is the international hailing/distress channel, and they dive in Cozumel and don't know that Channel 6 is the Cozumel hailing channel. This information should be disseminated to the tourists who may be carrying VHF radios in their dive gear for emergencies. Just a thought.

Cheers -

 

[kelemvor]

Aren't all VHF radios made to monitor ch 16 even if their preferred channel is another?

No. There's a features called "Digital Selective Calling" or DSC. I think every country uses it. In the US, all marine radios were required by law to support DSC as of 2009.

SOLAS is an international convention that also requires radios to support DSC. For Class A vessels (big ships, cruise ships etc) the vessels even have to serve as DSC/Emergency repeaters.
Information on SOLAS: SOLAS Convention - Wikipedia Edit: everyone except Bolivia, Lebanan, and Sri Lanka are a party to the SOLAS convention.

So.. even if you're listening to channel 7 on your marine radio.. if someone uses the emergency mode to broadcast on channel 16, everyone within range will hear that broadcast. If there's a class A ship within range, then a whole lot of radios will hear your broadcast.

Here's info on DSC from wikipedia: Digital selective calling - Wikipedia

Here's more detailed info from the US department of homeboy security: Digital Selective Calling

Here's info from the US FCC on Marine radio: Ship Radio Stations
Note that channel 16 is not the only reserved marine channel. For example, channel 6 is "INTERSHIP SAFETY - Use this channel for ship-to-ship safety messages and for search and rescue messages to ships and aircraft of the Coast Guard."

Obviously the FCC or DHS are not the world police, but I believe most countries take this stuff very seriously.

I was unable to find when DSC was created. My money would be in the 70's or 80's. A listening watch aboard GMDSS-equipped ships on 2182 kHz ended on February 1, 1999. I'm sure it was around a LONG time before it was decided that having a human simply listening to channel 16 was no longer going to be a thing.

Now, boats might be using radios other than marine radios in coz (I doubt it but you never know I guess). If they're using a marine radio made since 2009, they definitely support DSC. If they're using a radio made since 1999 it's very likely it supports DSC. If they're using a radio older than that, they should mail it off to the Smithsonian.

 

[Johnoly]

But generally is not automatic. The dual watch function has to be manually enabled.

And just to complicate it further,,,On one of our radio's we can set it to 'Scan/Watch' all channels. Which is annoying as heck. But like all jurisdictions if you are just sitting for 8 hours floating with a hook below, sometimes the conversations are very humorous. Which is why I'm glad that in southeast Florida we are so close to cell signals that we mostly just keep it private, sometimes even emergencies !

 

[seeker242]

So.. even if you're listening to channel 7 on your marine radio.. if someone uses the emergency mode to broadcast on channel 16, everyone within range will hear that broadcast. If there's a class A ship within range, then a whole lot of radios will hear your broadcast..

Technically it's VHF Channel 70 for DSC calls. I'm a GMDSS radio technician/inspector so I felt a need to correct that. Came into real use the same time GMDSS came onto the scene throughout the 90s. International Telecommunications Union (ITU) sets the international standards for channels which most radios follow. It's mostly the same channels everywhere, a couple differences, that's why with some radios you can switch between USA and International.

 

[Russjstewart]

And that's what I meant. Thank you for explaining it much better than I could. So if an emergency is heard on 16, the receiver can switch to 16 as needed for two-way communication. The distressed user can try his primary channel first, then switch to 16 if needed to hit all stations in range. Do I have that right?

Sort of, any transmission on ch16 will cause cause a radio that is set to dual watch to lock on to ch16 once the station transmitting the radio will go back to dual watch mode.On the radios I am familiar with If you are in dual watch mode and want to transmit on ch16 you have to go out of dual watch mode and select ch 16. A diver trasmitting on ch 16 will only be heard by stations listening to ch16 or set to dual watch. I know from personal experience a lot of boats will only listen to to the working channel they normally use. What the regulations say and what people do may not be the same thing. The best thing to do is to contact the dive op and ask what they listen to and preset the Nautilus life lone to that

 

[Russjstewart]

Technically it's VHF Channel 70 for DSC calls. I'm a GMDSS radio technician/inspector so I felt a need to correct that. Came into real use the same time GMDSS came onto the scene throughout the 90s. International Telecommunications Union (ITU) sets the international standards for channels which most radios follow. It's mostly the same channels everywhere, a couple differences, that's why with some radios you can switch between USA and International.

As an example of the differences between US and international channel scheme, the international scheme has CH 75 & 76 that the US does not, and a number of International duplex channels are simplex in the US. The main channel such as 16, 70 (dsc), 67 & 6 are the same.

Marine VHF Band Plans - The RadioReference Wiki
NB, edited after I re-read both posts so it makes a bit more sense