Ships have four speeds apart from Stopped. Full, Three Quarter, Half and Quarter Speed.
Ships can only use Full Speed a few times (usually three) in a game. The Captain has a Full Speed card(s) which he must hand over when Full Speed is ordered. Ships normally steam at Three Quarter Speed.
Engine damage will incremently reduce the speed options available to Captains.
When a turn is ordered the Turning Circle (actually an octagon) is placed in line with forward edge of the ship base, red for turns to port and green for starboard.
The ship is then moved round the Turning Circle according to the speed the ship is capable of steaming. Sharp eyed observers will note that a ship can only complete a full reversal of course at Full Speed.
Movement ahead is fairly straightforward (no pun intended).
Leading to something like: