500 ton threshold

Because the rules are designed for commercial ships. And there's a huge difference in passenger carrying capacity between a 500 GRT and 1600 GRT ship, among many other things........

It's mostly experience / sea time on appropriately sized vessels I believe. What is the reason you want to increase your tonnage? Are you in a position to move into a position that would require it or do you want to pursue commercial work? If not it could work against you as many will feel you might me too much of a sea dog for their family boat.

He's asking about Yachts over 500 GRT, not crew.

Is he?

Old saying from the Cruising Community: Go small, go now.

(Not related to your search on course) A classic example was this retired couple who were looking for the perfect cruising sailboat, it had to be big and it had to have all the equipment available: They found a Morgan 51, spent 10 years taking it apart and making everything and every piece perfect, all the latest gear, etc:
When they were finally ready to go cruising, the husband died from a heart attack.
The boat is still sitting at a dock at the New River 10 years later, it never went anywhere.

That's why 160-170' is such a popular size as they easily sneak under the 500 Ton mark. Even the 172' Westport is 496 Tons.

OR, find a smaller yacht with a builder willing to make a 6th guest stateroom. Many times there is a "Captain's" stateroom that could be used for guests or so forth and then adding an additional crew stateroom down below.

"Many will feel you might be too much of a sea dog for their family boat" ...
Ummm what?

Successfully making it all the way through your career to retirement is proof positive you've done it right. Not the only right way of course, but right.

People who spend their careers in commercial work tend to be a little rough around the edges for the more gentile.

Just curious to know if you have spent any time in commercial work? The more *genteel* clients might not agree with your broad brush assertion

Quite a bit. Everything from cleaning oil slicks, laying cable and transporting to launch work and picking up remains after a plane crash. Things like working on the water when it's below zero* or picking up body parts hardens a person and can make them more serious than someone sipping umbrella drinks as they play with their kids wants.

That’s great guys, but can we please just stay on topic?

It is on topic. The OP was asking what regulatory requirements were involved for a 500 GT. That sounded like he was thinking of going for his. Everything involved would be relevant so future readers can get educated. After several posts it appears that the OP is thinking about hiring a 500 GT, but while we're waiting for someone with a 500 GT ticket to respond about what regulations, if any beyond sea time are involved, the thread staying active increases the odds that 500GT will see it and respond. In the mean time I don't mind someone questioning my credentials. I have them.

No, the OP is thinking about buying a boat and wondering what he'll face if it's over 500 Tons ITC. I can see how you were confused but we straightened that out with post numbers 5 and 7. So none of this has to do with a captains license. Nothing here to do with your Sea Dog comment which we don't understand nor to do with Commercial vs. Pleasure. The thread topic is the requirements for owning a boat over 500 Tons and the costs related. Also not about oil slicks or picking up remains, none of which answers the question Kilbride asked you about your commercial boating experience, which I don't believe you ever were a captain on a commercial ship but perhaps you were. Capt J could have called you out but actually called Kilbride out for following you off topic. Now can we just stick to discussing the question Flying Golfer has.

To Flying Golfer. Far more regulations on staffing of the boat at 500 Tons. Not just qualifications of crew but crew required on board and crew responsibilities and scheduling of crew. Also, inspections and sign offs on the boat itself.

Depending on flagging and number of passengers may be subject to SOLAS, even SOLAS cargo ship rules, MARPOL, and flag state manning requirements. It's all manageable but it does bring extra costs and compliance issues. In fact, most boats that size will often have someone with just the task of compliance.

I would suggest talking to a maritime attorney experience with such boats before going too deeply into it.

Much of this has been discussed previously in a pretty informative thread:

https://www.yachtforums.com/threads/passenger-yacht-code.23476/