Technically speaking, for your own boat, you do not need a license to sail the world.
A couple of howevers are attached to the "technically speaking" phrase.
(1) Port authorities world wide are port authorities. They have lots of power because you can't defend yourself. They can request that you prove competence to sail in their waters. Having a License will go towards that proof. Additionally, you're more likely to have a port authority issue if there is an accident of some sort (perhaps even not your fault) and you can't prove competence. On top of all that, you are not exempt anywhere from the laws of that country when in their country so if you are lacking in their government required amount of fire extinguishers, for example, then without a license you are essentially proving that you don't know what you're doing (even if you do). Wisely speaking - you don't want to get in trouble with a port authority.
(2) Going through the proper procedure to gain a proper license like the NauticEd SLC or even the RYA Yacht Master program means you're going to be properly prepared and documented as such. If you're sailing across vast oceans you're better off going up a Rank to the NauticEd Captain's Rank which deals much more with offshore sailing. The old saying of "you don't know what you don't know" applies here.
So what licenses we recommend for global sailing?
- The RYA Yacht Master
- NauticEd Captain Rank with SLC
What do we not recommend as the be all and end all for global sailing
- State Boater License
- Canadian PCOC
- No ASA courses will suffice
It is a different story of you are renting a yacht. If you are going to rent a yacht in the Caribbean you just need to prove to yacht charter companies that you have a sufficient resume. If you are going to the Mediterranean you need to have one of the following:
- NauticEd SLC
- RYA Day Skipper
- The IPC will work but you definitely need to have a fully documented sailing resume