From: PDX (and now) London, UK
Out of curiosity how does a twin-screw help maneuverability? Can power be pushed to each individually to turn faster? Just a novice in this area so I'd love to learn more.
Go full ahead on one and full astern on the other. You twist--fast. Or go less than full on either and you twist less fast. Twin-screwed ships are a lot easier to land at a pier because they can do this. Single-screwed ships need tugs to do the same thing.
It's hard in an engineering sense to go from all ahead whatever to a twist. You have to stop one shaft (some ships have/had clutches and some don't) quickly and reverse the throttles, which really puts stress on a drivetrain, but DDs were built to do it. They were the sports cars of the warship world.
Edit: yep, multi-screwed ships have port and starboard screws. In quad-screwed port and starboard are separate as well, in groups. Orders to the helm are either "All_______ (ahead, back) + an amount (Flank, Full, Standard, Two-thirds, One-third, Stop, Emergency (sometimes; not every ship had an Emergency bell order.) Or they are split orders: "Port Ahead Full, Starboard Back Two-thirds" for example. Keeps the lee helmsman and the throttlemen jumping. Conning officers know how their specific vessel will react to every bell, ahead and back. It's practiced and practiced and practiced.
Wow. I've definitely seen what looked like that in ships pulling up to a dock, but I had no idea it could be used at near flank speed in he middle of battle to maneuver around torpedoes. In various films I've of course hear the split order for each screw but it somehow never clicked what was happening there.
"Success is the ability to go from one failure to another with no loss of enthusiasm." - Winston Churchill