In my Volvo MD 11-C I am using 15W-40 Shell Rotella-T. It is the same lubricant that the PO used for the 10-years he owned the boat. BTW, he worked for Shell and was on the team that developed the Rotella-T (he tells me) so I think he knew what he was doing in making that choice.
FWIW, I think Rotella-T to be an excellent product...MGM
Catalina 387 #29
Rock Hall, MD