If you are thinking of buying a boat - hold off, because the prices are going to be much, much lower in the fairly near future. Hate to be a harbinger of doom and gloom, but it's going to be another three months before it becomes apparent how deflated the US economy has gotten, and once business moves into survival mode, there will be some incredible deals to be had.
Thats going to work on both the buy and sell sides so, you'll still be able to upgrade if you like, you'll be selling cheaper and buying cheaper, but the transaction will still work.
If you have a substantial loan on a boat right now ... well ... hmmm ... get rid of the loan somehow. A lot of financial institutions are going to be calling in a lot of loans that they feel (rightly or wrongly) are not 100% gold-plated, tangible asset-backed, sure things. There will be a certain amount of overreaction on their parts, so be prepared.
Insurance will be the major boondoggle. They are going to get hit as well, so it's going to be hard to get them to write an agreed-value policy that inflates as the economy clears up and boats regain their value. In the case of the older boats, that may never happen regardless of how great their condition is. So - don't borrow money to buy an old boat.
Probably best to stick with one of the more "nautically-minded" insurance companies out there. They'll have at least a superficial understanding of what they are insuring, and it's market value.
The lucky people, as always, will be those who have cash in times of difficulty. There are certainly going to be some good prices next summer