A model is developed for the acoustic source strength of blade rate line energy produced by single‐screw merchant vessels. These source strengths are based on observed cavitation time histories on merchant vessels and on limitations imposed by considerations of propeller design procedures and ship vibration criteria. Relationships are presented for the expected value of the blade rate source strength for ships of different lengths, expressed both as a monopole source strength located at a known depth below a free surface and as a dipole source strength that describes the pressure radiated to the farfield. These relationships are based on a small sample of merchant ship characteristics and are exercised for the estimated population of ships at sea. This calculation yields a statistical description of the distribution of source level and frequency of propeller blade rate acoustic energy for the fleet of single‐screw merchant vessels.