When I was financing my first boat the bank looked at values in both books.
I'm looking for a new used boat and the bank I've been talking to wants a value survey from an accredited surveyor for at least the sale price of the boat.
I guess it depends on the lender.
It would be interesting to know how values are established...the books list values that are way way under asking prices. With older boats condition is everything so it seems like FMV would be set on a case by case basis. The books give a ballpark.
Boats are worth what someone will pay for them, and books don't buy boats.