There's a great article on the site for changing your oil for newbies (like me). The author uses 10-w30. But I see diesel motor oil on the shelf too.
What kind oil are you all putting in the M-35BC?
Jackfish Girl, 1999, C36 MKII, Tall Rig, Wing Keel, In-mast furling, Phinneys Harbor, Bourne, MA