A torpedo-shaped vehicle holding a side-scan sonar or similar sensor, towed on an armoured cable that carries power and data. Towing deep keeps the sonar near the seabed for better grazing angles and away from surface noise and vessel motion. Its position is computed from layback in shallow water and tracked with acoustic positioning in deep water, so contacts land in the right place.
Bring the towfish up, we're crossing the wreck and the chart says 6 metres over it.
Also heard as
- fish
- towbody
- tow fish
Related terms
Side-scan sonar
A sonar that images the seabed to either side of its track, revealing objects and textures by their echoes and shadows.
Layback
How far astern of its tow point a towed sensor actually rides, measured horizontally.
Flying the fish
Controlling a towfish's height above the seabed by adjusting cable length and boat speed.
Nadir gap
The unimaged strip directly under a side-scan towfish, roughly twice as wide as the fish's height above the seabed.