How deep the sonar sits below the water surface with the boat stopped, added to every measured range to give depth below the surface. It changes as fuel, water and crew load change, so it is measured at the start and end of each day and interpolated between readings. Static draft errors pass straight into every sounding as a constant bias and show up as busts between days.
Static draft's 0.62 this morning, we took on 400 litres of fuel last night.
Also heard as
- draft
- draught
- transducer draft
Related terms
Squat
The lowering of a vessel in the water as it moves, which must be added to sonar depths at survey speed.
Lever arms
The measured distances between sensors on a survey vessel, used to carry positions and motion to each sonar.
Bust
A vertical or horizontal mismatch between overlapping lines or surveys that exposes an error somewhere.
Bar check
A singlebeam calibration that hangs a plate on marked lines under the transducer and compares the sounder with each known depth.