You can listen on any frequency you want to. YES
Anyone can transmit on marine vhf PRETTY MUCH
The ham license (three levels) gives you transmit privileges on ham frequencies and modes. You have to take a test.
The marine ssb license gives you transmit privileges on marine frequencies on ssb, you have to pay money. PRETTY MUCH
Some boats carry both a marine ssb radio and a ham radio. A "ham" radio can include a lot of things not related to marine SSB as well as an HF SSB radio.
Some boats have a marine ssb radio that has been unlocked so it can transmit on ham frequencies. This is technically against the rules but it is almost impossible for anyone to know. NO - this is totally legal. I used to sell marine SSBs and some needed unlocking and some were that way stock. This is NOT illegal.
Some boats have a ham radio that can transmit on marine frequencies but they may be caught as the marine radios are built to a higher standard and some crusers have been fined and have had their radios confiscated. MAYBE
- it is technically illegal, but you would have to do something dumb to attract attention. Back in the day a certain shore station was so used to sailors using ham radios and ham radio PK-232 TNCs to connect to their SITOR service they new the right offsets for them
Still, with the flexibility of modern marine SSBs no reason to take the chance anymore.
Marine SSB radios are much easier to use than HAM.
Ham radios are much more flexible. There is almost always a Ham operator monitoring frequencies.
Most cruisers turn their Marine radio on only when they are going to use it as it uses a lot of power. So their may be no one to hear you. TRUE
Marine ssb radios are more likely to survive the salt air. The Ham radios will probably rust out after a few years. MAYBE
My Kendwood TS-440 has survived a decade of marine use. It is however, not waterproof at all. Direct salt water would kill it.
Did I get this all about right?
I know I left a whole lot out.
There is all kind of info about nets, packet radio, email, weather, position locating etc that I'm just learning about.
It would be great of someone could recommend a book or write a FAQ.
It is a big subject.
If I'm going to do anything with my license I need to buy a radio. I don't plan on getting a boat that I would even consider putting a radio in for a couple years I don't know what to buy to learn how to use one.