Storage Chest

If you are looking for the Bronze Pirate Chest, which can be commonly found in Pirate Camps or Old Pirate Ships, go here.

Storage Chest is a craftable wooden container that works both as a Ship Customization item and a container. The storage chest can store 18 items in it.

Source
It can be placed anywhere on any Boat and does not require a key to open.
 * Crafting - 4 Hardstone Ore, 6 Wood Log
 * Drop from Pirate Shipwright

Trivia

 * The capacity of Storage Chest is increased from 10 to 18 in the v1.9.6 Storms of the Sea.