Shore power does mean the vessels can turn off, or turn down, their diesel engines or LNG turbines while berthed. That reduces the carbon footprint while in the port. It also reduces noise pollution.
As for the carbon footprint of transporting the parts for the new footbridge - better to put them on a scheduled ferry service aboard Brittany Ferries' MV Pont Aven than charter an alternative. Although, of course, best would've been local manufacture.
Away from Plymouth, I didn't find the reason for it at the time - finding out the hard way that the Stromness Scrabster ferry, docked at Stromness overnight and running a bed and breakfast operation for passengers for the 06:30 morning departure, alongside the vessel (and indeed the cabins) on the quayside, a large and enthusiastic portable diesel generator (that hadn't been there for previous departures). But that's probably an Orkney thing...
Mark
