All of the class had smaller injectors and reprogrammed WEPS systems installed in 2008-2009 to make them more fuel efficient, and more suitable for the slow steaming that was becoming an industry standard.
Always used to be entertaining during my 12-4 afternoon watch, after we had been trundling along at 10kts, to soot blow and go up to 28kts and hurtle past everything. Used to get a few comments over the VHF!
Max sea-trial speed was 32.5kts (on the Buffalo I think). We managed 30kts during ours, but the weather was pretty crappy. Also managed 16kts astern.
They were built for WalMart to be the main customer. The idea was that they could load in China, go through Panama Canal, and discharge on the US East Coast faster than a conventional boxboat could cross Pacific, discharge in LA/SF and trains take the containers to the East Coast.
The theory was sound. At the time they were designed and ordered HFO was around $200 a ton. By the time they started to be built fuel was hitting $600 a ton. And when you burn 300 ton a day at full speed, that's a bloody expensive fuel bill!
Maersk tried all sorts to reduce fuel consumption. We used to sail with a contant head trim. Maersk had commisioned a Danish institute to work out the most efficient trim based on each load condition. Generally it meant a 1.5m trim by the head.
Obviously this complicated fuel uptake, bilge suction, FW suction, closing doors etc.
I have loads of pics of the Brownsville during final stages of construction, and of the Beaumont half way during build (including a few grainy pics of part of the M/E being lowered in) if anyone is interested.