LOts of us are husband/wife teams. You really should have a "Change of control" document. Assuming the very worst happens, the party listed on the ships papers becomes incapacitated or dies. The survivor
sails into port.
Some places the
boat will not be allowed to leave, nor can the survivor so anything with the
boat (sell f.eks), until the estate is settled.
A simple notarized document (or witnessed) saying something like:
In the event of my incapacitation or death, XXX assumes the position of
Captain with all the rights and privileges association with that position, including, but not limited to, sailing the boat onwards to any
destination, transfer of the boat to any
destination by any chosen 3rd party,
sale of the boat.
That's pretty clear language and will allow the survivor to retain control of the boat.