Great discussions and, as an owner of a 1983 Cal 31 that I have had for 14 year and absolutely love, I am in general agreement with Jeflaba's excellent overview of her blue water capability. His comment about the sealant failing on the forward deck hatch was something that I had not considered and really gave me pause. I now have another project checking and securing it for the spring. I sail mostly on coastal cruises in eastern NC and have occasionally ventured off shore to the Gulfstream. I have been through some bad weather (up to 35 Knots continuous in Pamlico Sound) but have never feared for the boat. Without a dodger and the boat's general low freeboard it can be quite wet. Around 1982 when Bangor Punta moved production of the CAL 31 from California to Florida, they switched from the plastic Beckson ports and moved to very solid Atkins and Hoyle aluminum with tempered glass. The fixed cabin side ports were switched from plastic to aluminum framed with tempered glass as well. I would say that this is much stronger arrangement. Prior to 1982, the similarly designed CAL35's and 39's, which are generally thought of as better blue water capable boats used the same plastic Beckson ports. They, too, around 1982 switched to metal ports. I have read widely that the companionway boards were simple butt joints, but mine came with stepped joints. I don't know if the previous owner had them made, but mine appear watertight. 2 Simple barrel bolts at the top secure them in a seaway.
As Jeflaba commented, if someone held a gun to my head and told me to head trans oceanic, I think it could be done successfully in a CAL 31 but, in my mind a 1982-1985 Cal 39 would be my choice for a more comfortable and safer passage. I haven't ruled out a jaunt to Bermuda or even down to the Caribbean or Bahamas in my 31, but for now coastal NC and a Cal 31 are perfect for me.