Water attenuates (reduces the power of) signals significantly and more-so at higher frequencies. The HF (3-30MHz) band is definitely not what you’d want to pick

Water attenuates (reduces the power of) signals significantly and more-so at higher frequencies. The HF (3-30MHz) band is definitely not what you’d want to pick (sonar is in the KHz range). The sub was probably still 27MHz but just higher power with a better antenna because of the FCC regulations though.