Good questions. Currently the largest ship in the world, in length at least, is EMMA MAERSK, the first in a class of eight ships. She is a container ship that is more than 1,300 feet long. She can travel at better than 26 knots, takes nearly five miles to come to a stop from full speed, and has a crew of ... 13! EMMA MAERSK has seven younger sister ships, all of identical length.
The longest ship ever built, SEAWISE GIANT (later renamed several times), was a tanker more than 1,500 feet long. She was scrapped in 2010.
If there is a logical, natural limit, I doubt that we have seen it. Perhaps the limit is not in the length of the ship but in the depth of the ship owners' pockets.
Ron Carlson, Webmaster