A quick google search yields:
https://www.uscg.mil/nmc/credentials/charter_boat_capt/ Looks like the usual government hoops you'll need to jump through - while throwing money at them the whole time.
Remember that it's not just about having a boat an getting your license. There are different standards for equipment on your boat when you're using it For Hire. You need to constantly keep up with the regulations.
How much will you charge? Per person or per group? How will you handle payment? Cash up front or will you figure out a way to take cards? What will you do in a no-pay situation?
Will you incorporate as a small business? Or just "wing it" and put your home and personal wealth at risk if you're sued?
Then there's people. God love them.
Anyone who's going to hang out a shingle (for any reason) needs to be able to handle people. First and foremost, you're going to need to be customer-service oriented. If you can't make your customers happy, you're not going to keep them. So if your idea of a "tour around the lake" is different from theirs it's YOU who's going to need to adjust your thinking.
Next, you need to be able to keep people under control for safety. If you don't have the stomach for constantly enforcing safety rules (Sir, please sit down. Mam, I need you to NOT sit on the gunnel! Please tell Little Johnny to stop slamming the storage locker door.) this isn't your gig.
Remember that you're going to run into all kinds - and they can turn on a dime. That kind gentleman and his wife that your friend's parents referred to you may turn into a couple of complete a-holes after they get a few cocktails in them. You need to have thought through handling all of this in advance.
I'd never do it for one simple reason: Stress. I hold myself to a very particular standard when doing anything "for hire." While I'm anal about my boat, it would be a HUGE stress point for me to have to maintain it and operate it "for hire." To me, that's a whole 'nuther standard. My boat is supposed to fun. As soon as it becomes work, I'll need another hobby.
So if you don't think any of this will be a big deal, get your license and go for it. Just make sure you've thought it all through. That picture you have in your mind of a pleasant summer cruise with everyone laughing and having a good time is the best day you'll have out there. There will be days on the opposite end of the scale that may make you wish you were teaching Summer School.
Just my 2 cents. (And I AM getting cynical as I get older so take it all with a grain of salt.)
