Draft (nautical)
From Wikipedia, the free encyclopedia
- For use in sailing, see draft (sailing)
In nautical parlance, draft or draught is the distance from the waterline to the keel and is the minimum depth of water required to float a vessel.
A quay's draft is the available depth of water at low tide.
A vessel's draft is the depth below the water's surface of the lowest part of the vessel, usually the keel. The draft of a vessel varies with the cargo, fuel, and ballast load, and with the density of the water. A commercial vessel's plimsoll mark indicates its maximum allowable draft. A vessel's draft, plus minimum allowed keel clearance determines the minimum depth of water that the vessel may pass through. Acceptable keel clearances vary according to several factors including the accuracy of the charts, swells, and the tide. Draft increases with vessel speed, this effect is known as squat. Riverboats are often purposely designed with a shallow draft to avoid sandbars and other obstacles. As such, a vessel's draft must be less than the draft of any quay it wishes to berth at. On larger vessels draft is measured at the bow and stern using draft marks. The difference in draft forward and aft is know as trim.
Related to the normal draft, is air draft which is the distance from the water line to the highest point on the vessel. Air draft, plus a safety margin, determines the height required for a vessel above the water -- this is typically quoted for bridges over waterways as well as any other restricitons such as power lines or tunnels.
de:Tiefganges:Calado fr:Tirant d'eau it:Pescaggio (nautica) pt:Calado fi:Syväys
