Ship improvements are improvements you can buy for your ships in the game. These typically are somewhat expensive, but cost less than hiring specialized staff.
Ship improvements are located at the bottom right of the screen and can be applied simply by clicking on them and purchasing them. Each one gives an additional passive benefit to your ship. (the exact extent of each one is unknown)
So far there are identified improvements: Copper Coating, Hammocks, Fine Gunpowder, Water Pumps, Improved Steer, Heavy Bulwark and Optimal Ammunition Deployment.
Copper Coating is a ship improvement that increases resistance to fire. This means it is harder to ignite the ship via bombs, oil barrels or powder barrels.
Hammocks increases the number of crew members which a ship can hold.
Fine Gunpowder is an upgrade which increases damage per shot from cannons. The exact increase is unknown.
Water Pumps (unknown)
Improved Steer increases the mobility of the ship. This means it is easier to turn and the ship handles better. The exact increase is unknown.
Heavy Bulwark increases the hull's hitpoints. This means it takes more damage to sink the ship. The exact increase in hitpoints is unknown.
Optimal Ammunition Deployment increases the reload speed of the cannons. The exact increase is unknown.