I believe it's usually just a tax play. If it's a personal possession, 100% of the maintenance costs are after-tax $$. If they actively rent it out (even for only a portion of the year), then only their personal use of the yacht (maintenance and costs during that time pro-rated etc) would be paid for in after-tax $$. The rest of the costs would be business costs for the charter business. I suspect the accountants would set it up so that the charter business actually invoiced them for their own personal use of the yacht to keep that separation clear.

I suppose it's possible to claim yacht expenses as business expenses for things like entertaining clients, etc, and in some cases that might be quite legitimate. But I don't think people get away with nearly as much tax avoidance shenanigans as most people think - The tax man isn't that stupid and trying to claim that sort of use for luxury products is just asking for an audit.

It might be different for super-yachts with really high yearly costs, but for the under 100 ft category of pleasure yachts that cost 10-30k per year upkeep I don't think the net benefit would be worth the complexity. At least for those _trying_ to play honestly. I'm pretty sure every lawyer/dentist/doctor etc that owns one asks their accountant the same type of question, but I don't believe most bother setting it up like that.

source: I own a pleasure craft/yacht big enough to charter regularly to offset the ownership costs, but don't do it on the advice of my accountant.