The Draft, as simple definition is the distance between the sea level and the bottom of hull (included the thickness of bottom – see this article)
But the confusions still happening sometime for the junior designer/surveyor during initial design stage/ dimension surveying.
That there’re two terms of Design and Scantling which making the story.
Hereby the clearly definitions:
- Design Draught, T-DESIGN – fundamental design excluded ship strength
The draft the vessel (and her deadweight, stability, performance, etc.) is designed for compact of calculation documents. Generally more draft means better seakeeping capabilities, but less draft often means more stability.
- Scantling draft (T-SCANTLING) – for ship strength design
The draft vessel structures are designed for (hull plating, tank bulkheads, etc.), i.e. the maximum structural draft for the vessel. Typically scantling draft is slightly more – make the magin strength for ship, than design draught or the same as below image. If stability requirements do not require otherwise, the scantling draft is the maximum draft to which the vessel can be loaded.
Further key basic knowledge in shipbuilding can be found at Essential Knowledge of Modern Shipbuilding Industry