And that is the reason why some people buy new every year. It's a math problem not well understood.
If you bought a boat every year for 10 years, 100k up front, 10k for the trade you would spend 190k over ten years.
But, if the dealer gave you a deep discount, and lets say for 7k on average you depreciate. 100k + 7x9 (1st year was 100) 163k
Winterized and storage, you'd save 15k over ten years. Lots do their own and the mileage will vary. 63-15 = 48k running total
Benefit of never off warranty, call that a wash because new boats every year will suffer some glitches every few years as boat manufacturers are not Apple, nor Rolex and engines have a 3-5yr warranty. As much as we are lead to believe everything is wonderful, it isn't.
Resale after 10 years, 85k which means 48k goes back to 63k in overall loss.
In the end, the guy who keeps the same boat for ten years discovers its worth 40k and observes 60k in depreciation.
Guy who upgraded every year loses about 63k. ... 3k difference, we should all be trading in, ah if that happened the depreciation would sky rocket. But in reality, if another 2008 kicks in, you could be in for a surprise.
Above is not fair math, I agree. The winterization could easily be off by 5-7k, tax loss on the upgrade (laws/rates are diff), new registration fees 500 and the big variable is the 7k of the dealer being nice, it won't always be 7k and could be off by 1k/year (9k over 10) or as much as 10-15k per year, 90-135k over 10 years.
Finally, if you finance the boat, add interest on the delta over the period. if we take the best case scenario of only a 3K difference and bump it by 800-1200 in interest...
To be a little more realistic, if the delta is 30k overall based on above miscalculations, interest would be 8-12k making the difference 38-42k, let's call it 40k.
Where the mistake is made, is to take this 40k, then base calculations on it. Like for 4k per year, I can save the maintenance - No, that was already part of the equation so don't double count a benefit. All of a sudden you're doing madoff-math.