[schoen]

> Obviously unlimited length can't be literal, if the Suez isn't perfectly straight, right?

It looks to me from the map like the tightest turns in the canal are the southern exit near Suez, and the turns between Timsah Lake and El Qantara el Sharqiya (depending on which channel you're in, and whether you're allowed to use both channels in your turning maneuvers).

It would be a fun problem to find a good way to figure this out exactly, but it looks to me like a ship 3000 to 4000 meters long would not be able to complete those turns even in principle without running aground. (Presumably the actual practical limit is a lot lower.)

The longest ship ever built (which exceeded the draft limits for Suezmax, so it was out for a different reason) was 458 meters long

https://en.wikipedia.org/wiki/Seawise_Giant

... so there might still be an order of magnitude to play with if you were making a ship that was ideally small and maneuverable in other regards.