Prince of Wales's shaft trouble supports the case for a three-shaft arrangement. A carrier could shut down one drive and retain two working shafts instead of losing half its propulsion. That redundancy would also let machinery rotate through preventive maintenance and could provide somewhat more speed. A hull roughly 310-320 meters long would offer room for the extra machinery without requiring a much broader redesign. Length beyond about 330 meters would make worldwide dry-dock access harder.
Chapter · 2:01:24-2:08:42
The case for a third Queen Elizabeth-class shaft
A third shaft could improve redundancy, maintenance flexibility, and speed, but would require a longer carrier and dockyard tradeoffs.