It is a confusing mess sometimes, but just remember, two different radio systems (Marine & Ham) with different requirements. And one license has no effect on the rights granted by the other license.
First the Marine side of it. To operate a VHF and SSB marine radios in international waters you need two licenses. First there is a Ship License. For this one, you can register your VHF, SSB, and obtain a MMSI number that will appear in the USCG database. This license will assign your call sign to your boat and is not transferable. Then, as an individual, you will also need a Restricted Radio Operators (RRO) license. Both licenses are obtained by just completing a form and paying a fee.
On the ham side, you must test to obtain the right to broadcast on the allotted bands. For the most part, if you are looking at a radio like an ICOM M802, you will need to obtain a general license, which means two tests. But with a little studying, neither is hard. If you have an 802, I would encourage you to get this license.