You do keep the same USCG documentation number. That should be permanently affixed somewhere on the inside of the hull
or on a bulkhead so it cannot be erased or altered. USCG wants you to epoxy
over it so if it is tampered with, there will be visible signs. You need to know where yours is--the USCG will ask to see it when doing safety
checks. Need to keep original copy of USCG documentation certificate aboard.
You cannot keep the old call sign or MMSI. FCC will issue you new ones for a lot of money
, albeit for a ten year period. I believe if you only operate your boat in US waters you can get away without a radio
telephone operator license
and you can get a free MMSI from BoatUS. You won't have a call sign, but most people use the boat's name when hailing on Channel 16. But if you go into international waters, you need both a FCC radiotelephone operator license (free and for life; no test), a ship station permit
which comes from the FCC and costs and gives you a call sign, and you need a FCC issued MMSI. That comes with the ship station license. The BoatUS MMSI is not valid for international waters.