One of the main plots in my world is that a huge ship arrives in a strange group of isles. This ship a gigantic city that completely self-supports itself with farms, houses, gardens, parks, and even recreational facilities. It has a population of 10,000 people called the Explods. There is even a government and class-system on the ship. The most interesting thing is, the ship has been going on a non-stop voyage for more than 1,000 years. This means that it has not stopped at any ports, seen any other ships, or had contact with outside civilization.
Is this plausible? What do the conditions of the voyage for this to possibly be able to happen? Would there have to be multiple ships? If this is not possible, then please tell me how it could change to be possible.
Also, there are no wars on this ship, and the people are fairly like-minded. The reason why the ship even exists is because of a legend of treasure at the end of a giant ocean. A small group of people who went on this journey built a huge ship in order to try to survive this journey. Over time this ship was expanded by the descendants in order help sustain the huge growing population.
Edit: This ship is not a very modern ship and the people who built it do not have access to steel and extremely durable substances.
This ship is in the water.
This world is not at all like Earth and has an almost unimaginably big ocean with nothing in it except for sea creatures, and this ocean separates two major landmasses.