Is an entirely sailing-ship based civilization feasible?

Question

I'm picturing a city-state was destroyed by rising sea levels. Rather than scatter or build dams to protect the city, they took to the seas, a 'city-fleet' of sailing ships that travels the oceans fishing and raiding.

Before I start working out details like population, ship types, culture, and magic, I want to know: is such a thing feasible? Would they be able to believably sustain themselves while still traveling as a fleet?

Since the ultimate fate of this civilization is to be wiped off of the map by a localized event (angry sea goddess), the majority of the people do have to be on the ships (it can't just be the naval force of a land-based people) and the majority of the ships do all have to be traveling together.

Potentially relevant setting details:

• The world is much more aquatic than Earth. The continents are smaller, and islands are much more common.
• Mermaids and other aquatic cultures exist. Potential sources for trade.
• 'Medieval' is my starting assumption for technology level. This is not locked in.

Answer 1

• How long do the ships last?
  Historically, a single season in tropical waters could ruin a wooden hull. Shipworms, rot, storms, and so on. Wooden ships would be careened every couple of months, pulled onto a beach and scraped. How do they do that on the water? If they cannot, the ships will last a few years.
  Magic might help here.
• Where do the ships come from?
  Regardless of how long the ships last, there will have to be new ones. Historically, this starts by growing large trees, cutting them, drying them, assembling the frame and planking them. That is done on land.
  Imagine very large rafts where ships are built. There would still be the question of where the materials come from, and also where the large rafts are assembled. In sections on other rafts?
• Where do they get food?
  Fish and seaweed are probably not a balanced diet. Is that where the trade with the merfolk comes in?

Or consider a situation where the "sea people" and the "land people" are distinct ethnic groups, yet mingling all the time in the ports. The "sea people" buy ships from the "land people" and crew them, paying with the money they earn by hauling freight for the landlubbers who do not dare to cross the ocean. (Yet how do the "land people" manage to build good ships if they never sail them?)

Look at the trade winds and seasonal travel in history. Say your ships are not very good at tacking against the wind, so all those who want to make the trip that year start out at roughly the same port, at roughly the same time, to catch the trade wind. All those who do not join will not earn money that year ...

Answer 2

We have people like that right now. The Bajau people have been living on the sea since prehistory, long enough that they have evolved special physical adaptations for diving.

They've been doing it since the stone age so your people shouldn't have an issue. They live off the sea and trade surplus with land dwellers for essentials.

Also fleets of sailing ships could and did spend years at sea, only coming to land to trade, shoot some natives, dispense some diseases and refit their ships. Captain Cook & Abel Tasman for example.

Answer 3

A sailing fleet needs sails

I upvoted o.m.'s answer, but there is an additional key supply issue - textiles. After food production, textile production was the most time-consuming activity for pre-industrial societies. Note that for most societies the uses of textiles were primarily for clothing and bedding - curtains, wall hangings and rugs for the floor were luxuries for the rich. However, by definition the proposed sailing city-state requires sails for every vessel - this requires an enormous amount of canvas, with a limited lifespan in constant use.

Sailing vessels also require large amounts of cordage - ropes of various strengths and diameters for rigging and other uses. Cordage was also extremely time-consuming to produce, it is only less notable in pre-industrial economies because the quantity required was relatively low for land-dwellers.

With medieval technology there is no feasible way for the fleet to produce the textiles (primarily canvas) and cordage it requires. (Actually, while the city was still on land it would have been unable to produce or buy enough sailcloth and cordage to take to the sea in the first place.) It is implausible to believe that there are sufficient warehouses full of canvas and cordage waiting to be looted anywhere, let alone in settlements small enough that raiding will be successful. (Note that the naval battles required for raids will result in the loss of both canvas and cordage, as the sails and rigging of a sailing ship are routinely targeted.)

I am not even going to start on metalwork - I believe the fleet would have enormous difficulty replacing iron objects as they rust out in the sea air, but it is less of a problem than the textiles.

TL;DR even if the fleet can somehow magically overcome the issues of ship repair/replacement and food/water that o.m. raised, they will be literally dead in the water due to lack of sails unless immense quantities of sailcloth and rigging can be magically conjured from nothingness.