47 C.F.R. § 80.753
Signal strength requirements at the service area contour
(a) The requirements for reception by a marine VHF shipboard receiver are satisfied if the field strength from the coast station, calculated in accordance with § 80.771 is at least + 17 dBu above one microvolt.
(b) These field strengths, voltages and powers at the receiver input are equivalent:
(1) −132 dBW (decibels referred to 1 watt).
(2) 1.8 microvolts across 50 ohms.
(3) + 17 dBu (decibels referred to 1 microvolt per meter).
(4) 7 microvolts per meter.