What is the term for depth of water needed?

The term you are looking for is "draft". It refers to the depth of water that a vessel or ship needs to safely navigate without striking the bottom. Different vessels have different draft requirements based on their size, design, and purpose, and it's vital for safe navigation that they operate in waters with depths matching or exceeding their respective drafts. Knowledge of a vessel's draft is important for navigating waterways, harbors, and docks to avoid groundings and potential damage to the vessel.