Actually, boats don't have that much in common
With cars. An old car is likely to have a rusted "hull"...but an old fiberglass hull can last forever if it's protected from moisture intrusion. Vehicles don't have much in the way of systems--just an engine, heat/ac...a boat is a floating self-contained dwelling--with systems that do indeed wear out, but are replaced. It's VERY unusual to find a 30 yr old vehicle still on the road--or anywhere except a classic car collection...but there are a zillion 20-30 yr old boats on the water...and while many are indeed dilapidated, just as many of 'em are essentially 2-5 yr old boats that just happen to be in 20-30 yr old hulls, 'cuz everything on 'em has been recently replaced/updated/upgraded. They don't cost any more to maintain than newer boats. And the best part is, you can buy 'em for a fraction of the price of comparable new, or even 2-5 yr old boats. Even if you had to replace everything on one yourself, in most cases you can do it all for no more than the survey value will be when you're done.
With cars. An old car is likely to have a rusted "hull"...but an old fiberglass hull can last forever if it's protected from moisture intrusion. Vehicles don't have much in the way of systems--just an engine, heat/ac...a boat is a floating self-contained dwelling--with systems that do indeed wear out, but are replaced. It's VERY unusual to find a 30 yr old vehicle still on the road--or anywhere except a classic car collection...but there are a zillion 20-30 yr old boats on the water...and while many are indeed dilapidated, just as many of 'em are essentially 2-5 yr old boats that just happen to be in 20-30 yr old hulls, 'cuz everything on 'em has been recently replaced/updated/upgraded. They don't cost any more to maintain than newer boats. And the best part is, you can buy 'em for a fraction of the price of comparable new, or even 2-5 yr old boats. Even if you had to replace everything on one yourself, in most cases you can do it all for no more than the survey value will be when you're done.