There is a lot of water

The guide to naval warfare is long and detailed. The rules themselves are fairly simple and succinct. Below is a chart detailing material and construction point costs, crew requirements and transport capacity of the various ship types. The various sizes of roundships are designated by displacement.
As you can see larger ships get exponentially more expensive and take longer to build, while transport capacity doesn't keep up. As you can read in the guide to naval warfare larger ships have a distinct advantage in battle; their cost reflects that. They're still a good choice for fighting ships, but for mass transportation smaller vessels are more efficient.

Hull Material cost Point cost Crew Transport capacity
100 tonne hull 0.15 1 20 50
1000 tonne hull 15 50 300 1000
250 tonne hull 0.5 2 30 100
400 tonne hull 2 5 60 250
600 tonne hull 5 15 100 500
800 tonne hull 10 30 200 900
Horse transport 0.5 2 30 120
Longship 0.1 1 5 50
Small craft 0.05 0 5 20



Crew

Like troops the crews of ships have various grades of training, but in contrast they have fewer such grades. The reason for that is that not every sailor on a ship is as qualified as the next: there will be more and there will be less experienced hands, for experienced hands are always necessary but there are never enough of them to crew all ships sailing around. Training grade is reflected in how well the ship is handled and how well the crews can fight themselves.
Yes, crews can and will defend themselves. They're equipped with a variety of hand weapons and part of the crew will have bows. In a fight they can be compared with troops with a low training standard.

Shipbuilding

Shipyards are necessary to build ships. Ships cost materials and construction points. Construction points are the capacity of your shipyards: each shipyard has 100 points per turn, expanded shipyards 200. If you don't have a supply of wood, shipyards only have a quarter of their normal points.

An example fleet

Here are some examples of the ships that sailed under the flag of the city-state of Ladasa.

Airships

Airships in World of Arl are pretty basic, they're more akin to a hot air balloon than the common "Zeppelin" image normally conjured by the word Airship. Airships are constructed by shipyards and will benefit from the shipbuilding tech. Airships are listed according to how much they can lift. A basket to hold the crew is already taken into account, you need only worry about the crew and what they carry. Airship crew can be trained but there is no point in taking it above normal training.

Hull Material cost Point cost
1000kg Balloon 10 50
160kg Balloon 1 20
1800kg Balloon 15 75
350kg Balloon 3 20
650kg Balloon 6 45