The circle has a radius of roughly two ship lengths - but how did the circle stay that long in the first pic? Strange.Well, I gave a look at my navy books and didnt find anything about BB and DD turn radius at various speeds.
Anyway there are some famous pics (for example some taken during the battle of Midway) of axis BBs/CVs engaged by dive bombers and/or torpedo bombers that give an idea about how well could those monsters maneuver at medium/high speeds ... I know we cannot estimate *exactly* their speeds but for sure turn radius in ERT looks weird ...
[No need to post the pics again, so please look above. Ulsterman]
The second picture however strikes gold. It shows the carrier Akagi at high speed (~30 knots), I've seen the picture before. Akagi was laid down as a 35,000 ton battlecruiser (which is close to the real Hood class) and ended up as a carrier following the Washington Treaty. Fully loaded it had some 36,000 to 41,000 tons (It's difficult to give exact values, as sources give very different information about displacement).
Akagi was 855ft /260m long, so you can estimate. The trail is about 1.5 kilometers long (estimated, using the ship's length as measurement), and it's a turn of roughly 90?. At 30 knots you travel the distance in about 100 seconds.
Although it's a very rough estimation you could say that you should be able to perform a 180? turn with a BC at flank speed in 3 1/2 to 4 minutes, and your turning circle should have a diameter of about 1900m, a little more than a nautical mile.
EDIT: I found some data at hmshood.com. Close to the bottom of the document you can find a table about turn times and speed lost duing turns. I think these rates are those promised by the shipyard/admirality and were a little worse in reality, and of course they don't consider bad weather.
