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The draft or draught of a ship is a determined depth of the vessel below the waterline, measured vertically to its hull's lowest—its propellers, or keel, or other reference point. [1] Draft varies according to the loaded condition of the ship. A deeper draft means the ship will have greater vertical depth below the waterline. Draft is used in ...
Draft, Air – Air Draft/Draught is the distance from the water line to the highest point on a ship (including antennas) while it is loaded. Air draft is the minimum height a ship needs to pass under, while standard draft is the minimum depth a ship needs float over.
The process of determining a vessel's displacement begins with measuring its draft. [3] This is accomplished by means of its "draft marks". A merchant vessel has three matching sets: one mark each on the port and starboard sides forward, midships, and astern. [3] These marks allow a ship's displacement to be determined to an accuracy of 0.5%. [3]
At a basic level, it is typically calculated in metres using the formula: Charted Depth − Draft-/+ Height of Tide = UKC. [3] Ship masters and deck officers can obtain the depth of water from Electronic navigational charts. [2] More dynamic or advanced calculations include safety margins for manoeuvring effects and squat. [7]
The load line is a waterline that corresponds to the maximum draft of the ship, thus yet another name, load waterline. [2] Varying water temperatures will affect a ship's draft, because warm water is less dense than cold water, providing less buoyancy.
Influence of mainsail draft position on forward and side force. In nautical parlance, the draft or draught of a sail refers to the amount and shape of curvature in a horizontal cross-section. [1] Any sail experiences a force from the prevailing wind just because it impedes the air's passage.
The vessel's clearance is the distance in excess of the air draft which allows a vessel to pass safely under a bridge or obstacle such as power lines, etc.A bridge's "clearance below" is most often noted on charts as measured from the surface of the water to the underside of the bridge at the chart datum Mean High Water (MHW), [3] [4] a less restrictive clearance than Mean Higher High Water ...
Squat effect is approximately proportional to the square of the speed of the ship. Thus, by reducing speed by half, the squat effect is reduced by a factor of four. [2] Squat effect is usually felt more when the depth/draft ratio is less than four [2] or when sailing close to a bank. It can lead to unexpected groundings and handling difficulties.