I just read a question on the Roamer Club Forum if it makes sense to insure an older yacht for full value. The participant raises the question if you restore an older yacht that you have made a major investment in will the insurance company pay that amount in a settlement of base it on the book value of the boat? Interesting question, anyone know the answer?
I think it is the same as when you insure a valuable painting, or a car that is exceptional. In french they say "expertisée", meaning a specialist in the field has checked it out and documented it. Talk to your insurer about it, they must have or know people that can inspect your boat.
there are no real "book value" for older boats, at least values that mean anything. Normally policies are issued for a stated value determined by survey although insurers may question requests for values that are significantly higher than normal. You may have to do some shopping and negotating to get the coverage you want.