Merchant Shipping (Safety and Load Line Conventions) Act 1932

8 The main transmitter shall have a normal range of 100 nautical miles, that is to say, it must be capable of transmitting clearly perceptible signals from ship to ship over a range of at least 100 nautical miles by day under normal conditions and circumstances, the receiver being assumed to be one employing a rectifier of the crystal type without amplification.(1)

(1)

Unless a more precise and practical method is available to determine the range of transmitters it is recommended that, as a guide, the following relations between the range in nautical miles (from ship to ship under normal conditions in daytime) and the power of the ship transmitter in metre amperes for 500 kilocycles per second (600 m.) be used :—

100 nautical miles	60 M A
80 nautical miles	45 M A
50 nautical miles	25 MA

M being the actual height in metres of the aerial from its highest point to the load line.

A being the current in amperes measured at the base of the aerial in case of B, or fully modulated A2, transmitters.