A method that proves clearance mechanically rather than by sounding. In a wire drag, a wire held at a set depth by floats and weights is towed between two vessels; if it passes without catching, the area is swept to that depth. Charts mark swept depths with a special symbol because they guarantee nothing rises above them. Sweeping is slow, but it catches pinnacles and masts that acoustic methods can miss.
Area's swept clear to 11 metres, only one hang near the old pier and the divers cleared it.
Also heard as
- wire drag
- wire sweep
- bar sweep
Related terms
Hang
In a wire drag sweep, the moment the wire catches on an obstruction, and the obstruction that caused it.
Least depth
The shallowest depth over a wreck, rock or other feature, which is the value that gets charted.
Obstruction
A submerged object that hinders vessels or fishing and is not a wreck or natural rock, such as piles or debris.
Wreck
The remains of a sunken vessel, charted as a hazard or a feature depending on its depth and size.