The minimum draft is a specification referring to the least amount of draft a boat can have. In many cases, it is the same number as the maximum draft. In other words, not much on the boat can change the draft. In the case of a swing keel or centerboard boat, the minimum draft refers to the draft when the keel or board is drawn up. Maximum draft refers to the draft when the keel or board is fully extended. On powerboats with stern drives or outboards, the same numbers mean when lower units are fully down versus rigged for shallow running. The minimum draft can also refer to the boat's draft when lightly loaded. Larger boats ride lower in the water when fully loaded, and therefore have deeper drafts. The draft of a cargo ship, for example, changes by as much as 20 or 30 feet between being empty and fully laden.