documenting days at sea for OUPV

[Summer Berklee]

I think this is an older post, but I can't find the answer to this question on Google:

In order to be able to document your 360 days of sea time, what can you do to prove experience if the owner of the vessel that you sailed/crewed on for most of your life is deceased?
(father)

I will need to do the 90 days because I've only had scattered crew work on the west coast in the last 3 years but I'd hate to lose the bulk of the sea service.

Thank you!