Chinamax means ships that can use specific harbours, which imposes a length limit. Panamax likewise has a length limit because the ship has to fit inside the locks in the Panama Canal.

The Suez Canal doesn't have locks, so in principle the length isn't limited. In reality it of course is limited by the harbours you intend to use. Apparently ships longer than 400m also require permission from the Suez Canal Authority.

More important for the claim that Chinamax is bigger is the tonnage. Chinamax can carry 400,000 tonnes, while Suezmax is typically under 200,000 tonnes.

> 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.

I am not an expert but what I think they mean by 'unlimited' in this context is 'limited by engineering, not limited by 'geology of man made structure.'