Draft (water)

Draft in the context of water, most commonly refers to the depth of water a vessel displaces. It is the vertical distance between the waterline and the bottom of the vessel's hull (keel). It indicates the minimum depth of water a ship or boat can safely navigate. A vessel's draft is a crucial factor in determining where it can travel, influencing access to harbors, canals, and other waterways.

Key Considerations:

• Loaded vs. Unloaded Draft: A vessel's draft will vary depending on the weight of its cargo, fuel, and passengers. The "laden draft" represents the draft when the vessel is carrying its maximum allowable load. The "light draft" refers to the draft when the vessel is empty or carrying a minimal load.
• Draft Marks: Vessels are typically marked with draft marks (often in Roman numerals or metric measurements) on their hull to indicate the current draft. These marks are vital for navigation and safety.
• Air Draft: While "draft" commonly refers to the underwater depth, "air draft" refers to the vertical distance from the waterline to the highest point on the vessel. This is important for clearance under bridges and power lines.
• Relationship to Displacement: A vessel's draft is directly related to its displacement – the weight of water it displaces. The deeper the draft, the greater the displacement, and the heavier the vessel.
• Trim: "Trim" refers to the difference between the draft at the bow and the draft at the stern of a vessel. Ideally, a vessel should be trimmed evenly, but variations can occur due to load distribution.
• Fresh Water Allowance: Saltwater is denser than freshwater. Therefore, a vessel will float slightly higher in saltwater than in freshwater. The "fresh water allowance" (FWA) is a calculation used to determine how much a vessel's draft will change when moving between saltwater and freshwater.