I just replaced both bulbs this weekend on my 85 Ericson 30+. It has the old style Forespar combo deck/steaming light. Top (steaming) light is a trade #1416, 10W single bayonet (think it is a "C" base) - they have them at West Marine. The deck light is a larger single bayonet (think it is "G" base) trade # 1383, 20W which they also have at West Marine for $16. I saved some money by finding an Anchor replacement bulb ($5) with the same flared shape and wattage at a local Chandlery in Oakland (Sea-power). Suggest you stick a flag of tape on the face of the bulb to make a handle for installation - hard to get your fingers in the tube to turn without this trick. Be careful when removing the metal clip from the bottom of the deck light tube. I failed to catch the lens and after a 25' fall, it shattered into a million pieces - had to fab a replacement our of plexiglass.
Have fun!
Ken E
"En Route"
Alameda (soon to be Monterey), CA