Well, okay....the diving was great but spending 5 consecutive days on a resort boat with an incessant close talker made me want to jump overboard with Andre the giant's weight belt around my neck and no BCD.
If I had to hear one more story about his dive vacation trip to wherever the hell it was, I swear I would still be swimming back home right now.
I like the chatty ones. It means I don't have to talk.
.... and as you can imagine I've probably been the chatty one ..... from time to time.
When I'm in close quarters with people for an extended period of time, however, I eventually get saturated and need "down time".
I have this at home, where I sometimes spend entire evenings either working or behind my PC on social media "in my own head". I use meditation for this as well. I can also have it at my work where I am often in roles where I am required to communicate a LOT .... my job involves a freakish amount of communication at all kinds of levels, from the guy digging a hole in the ground with a shovel to the board of directors who doesn't know what end of a shovel you need to hold. There are days that I come home and the LAST thing I want is to talk to another person. It's worse when stuff I'm working on gets in the papers, I absolutely hate that. It's the worst thing about my job because journalists are universally incapable of writing down a single fact without making some kind of fantasy story to go along with it..... I hate that almost more than I can put in words. My wife, who is a natural communicator, doesn't always appreciate that need to switch off. She's gotten used to it, but she doesn't always appreciate it.
I dive, in part, for this reason. I love that you can be under water and having a shared experience without the need to talk the whole time. I need the "off switch". I don't mind being around people in the least but I like to be around people who can sit in silence for extended periods of time and not find that uncomfortable. I used to think that this made me awkward in social situations because I came off as being very introverted (and I am introverted to a point) but in actual fact I think the ones who have trouble being quiet are probably the awkward ones.....
So on a boat if someone were cramping my down time I would just say it. I wouldn't be rude as some people suggested. I would just say, "I don't want to blow you off but I really need some downtime right now and I would like to just go somewhere quiet for the next X amount of time".
That might sound pretty direct to some people but that's just putting it out there like it is. No beating around the bush. No blame, no aggression, just setting a boundary and being absolutely clear about it. And this works. 99 times out of 100 people accept this kind of thing without hesitation and without it escalating into a discussion. Moreover, if you come back to the same person again and strike up a conversation after you have had your downtime then the contact is usually on a more even footing.
Just a thought. Being assertive may strike some people as being difficult but in actual fact NOT BEING assertive gives you a lot more stress in the long run.
R..
No need to be rude or pi$$ anyone off. I might want to have a beer with them later. 
I'm glad the diving was good apart from this. Maybe you have a very approachable and comforting vibe you give others. 
