Upgrading my 500GT master NEAR COASTALl to OCEANS?

I’m trying to find out what is necessary to do this rating upgrade. I have had my 500 GT master near coastal for some time and would like to upgrade to an oceans rating. Does this require ocean sea service time as well as celestial nav? Please help. Thanks much!

This has been covered a multitude of times on this site…
That being said…
Almost any celestial nav. Class will suffice, a certificate from the class sent to NMC within one year of completion along with a complete application.No testing required at USCG REC at this level.