I don't think it's particularly smart to get into a cruising boat as an investment. While you might be able to sell a boat for more dollars than you paid for it, it seems that the additional dollars don't amount to much when you roll in inflation and the changing value of the dollar.
For example, in 1998 we paid almost twice in dollars what our boat sold for new in 1973. But when you roll in inflation and the changing value of the dollar, we actually paid less than half what the boat had sold for new. And this is a "high end" boat, at least in theory.
There are certainly exceptions, and the circumstances of every buyer and seller will dictate how much "value" a boat retains over it's most recent selling price, as will the boat's condition.
I know a couple of people who sold their boats for more than they paid for them even accouting for inflation and the changing value of the dollar. But..... if you added in the amount of money they had spent on the boat over the years they owned it, they in fact lost a fair amount of money on the boat.
Our own view when we bought our boat was that we would never see a dime out of it. We were buying it as something we wanted to do, and whatever the boat and the cost of owning it amounted to in the end was the price we paid (and were willing to pay) to have the experiences having such a boat would give us.
I don't know what we'll do with it when we can't use it anymore. Sink if for a fish habitat if that's legal is one thing we've talked about. Willing it to somebody we think might enjoy having it. Or we might sell it. We'll do what we do when the time comes. But we don't expect to realize any sort of profit, let alone a break-even return on what we've spent. If we hadn't spent the money on a boat we'd have spent it on something else with no return other than the enjoyment of the experience--- travel, horses, who knows.?
I think the only sure way to make money on a boat is to buy a collector boat--- a Hacker Craft, Gar Wood, classic Chris Craft, etc. Like collector cars, these retain and often increase their value simply because of what they are and the fact they are relatively rare.
But a production cruising boat is like a Honda--- it might be working well when you decide to sell it, but there are a bunch of them around and the market is pretty saturated. It's just an old boat, and the market will pay what it pays for an old boat. Which is generally less than what you paid for it when it was a less-old boat.