“Are they gas/turbine?”
That I Don’t Know. I’ve tried to find out much about them in years past as they fascinated me at the time. Sealand’s terminal was directly across the bay from the terminal I worked at in Long Beach, Calif. I saw some SL-7’s only a few times. Incredible ships!
From the scuttlebutt I’ve heard about them, their horrendous fuel consumption problem (which was the cause of their demise as commercial vessels), and the myths about their published speed versus their rumoured speed, I’d guess they were gas turbine. (I heard rumour to that effect, but never read confirming data.)
Most of the Containerships of the era were Steam Turbine, and quite fast (again as I stated in the original post, the theory at the time was speed was everything to compete in the trade), but soon (Mid ‘70’s) the costs to operate the vessels forced them all to slow down with more economical Diesel.
I was involved in shoreside vessel support and Containeryard management in those days. Never was involved in the actual vessel operations.
Sometimes I wish I’d been in the Navy instead of Army. I’d have been more alert, and questioning of details at the time, I’m certain.