A theoretical scheme to describe the infrared contrast field left by a surface ship on a body of water is presented. Starting from a field velocity distribution behind the vessel, the fluid mechanical behavior of the disturbance is developed as it interacts with the vertical thermal profile of the water and produces a temperature pattern on the sea surface. As a result, the signal sensed by a remote detection system is obtained. A detailed sensitivity study of the computational results is conducted by separately varying each of the main code variables. This method yields program input values that best fit the measurements. Using a bell-shaped velocity distribution as an input, the contrast radiant intensity of a natural macrowake generated by a catamaran is computed to be -225 kW/sr. This compares with a measured value of -298 kW/sr, from which it differs by about 24%. The variation of the spatial width of the macrowake on the water surface is computed and found to fit the measurements. An infrared gap is sometimes observed at the onset of the macrowake. Actual imagery of a catamaran and a monohull ship shows definite evidence of gaps. Their extent can be predicted by the theory to better than 5% accuracy.