I have an older Lifeline with the radio. I may be mistaken so if I am please someone correct me. It is my understanding that if I activate the alert the DSC that signal is broadcast and any boat with an equipped radio who is in range (this will depend on line of sight and their antenna height...) will pick up the signal and location.
This is essentially correct. If the DSC equipped VHF is properly connected to the vessel’s chartplotter, the location info from the distress call will also appear on a capable chartplotter. Usually they are connected via NMEA 0183. NMEA 0183 is a frustrating standard as each manufacturer chooses the colors they want to use for each of the functions. NMEA 2000 is much better, but not avai on a lot of VHFs. So, what you end up with is lots of boats (I’ve seen estimates of at least 90%) don’t have VHF and chartplotter connected properly.
The MMSI number is my registration and will indicate it is me. It is my understanding that I do not need to program it for each boat I am going to be on. It may be possible to do so and that if it is possible it may only transmit to that boat (for a period of time?).
This part isn’t exactly right. First, the MMSI is supposed to be assigned to a vessel, not an individual, though the vessel owner is normally included. Changing MMSI once set is usually not permitted by the user. All capable radios allow MMSIto be set by the user once, but generally don’t allow it to be changed. Idea is that it stays with the boat. The MMSI registrar should have a means to update the contact information for a particular MMSI number, but you won’t be able to change from it to whichever boat you happen to be on. I suspect this is why Nautilus discontinued the original model, as they were using an interpretation of the MMSI rules that may not have been entirely correct. I’m not quite sure how the new version handles that.
Also, if you press the red button, it won’t just transmit to the boat you are diving from.
I would rather it transmit to every boat possible if I deploy it. There is a lot of boat traffic where I mostly dive, Coast guard station not too far, Navy, Airforce facilities close by as well. I don't think I will be at sea too long even if it feels like forever. If I think it has been too long I will then deploy a PLB. I like the Idea I can send a voice request and hear back that someone.
That’s closer to what happens. When you press the green button and talk, any vessel tuned to the same chat channel will hear and be able to talk to you. It’s a good idea to have this be the same chat channel that the boat you are using listens to.
When you press the orange button, every vessel and shore station tuned to Channel 16 receives the transmission. This is an emergency channel, so is monitored by USCG in the US.
When you press the red button, a signal is sent to all DSC equipped radios (and the CG) that contains MMSI and location. This comes through a different channel that all DSC equipped radios listen for.
Essentially each button on the original Lifeline has different uses.
Green: You surface a little farther from the boat and want a pick up, but no emergency.
Orange: Your boat didn’t respond on Green, but you need to get their attention. And/or there may be an emergency.
Red: You surface, can’t see your dive boat, conditions deteriorating, help needed.