V primerjavi s sonarjem je ta af precej milejša opcija za podmorsko življe.
Short answer (TL;DR)
Ultrasonic antifouling:

Effective range in water: centimeters to a few meters at most

Practically “heard” only in the hull itself, not the surrounding water
Marine sonar:

Effective range: hundreds of meters to many kilometers

Designed specifically to propagate through water

So: sonar travels 1,000–1,000,000× farther than ultrasonic antifouling.