ShipEM is based on the Weaver dipole model which was developed in the 1980's by the Canadian navy based on the work of Dr. J.T. Weaver of the Pacific Naval Lab.  The program calculates the quasi-static, electric and magnetic fields of an Hertzian dipole embedded in a two-layer, conducting half-space, such as sea water over a sea bed.  The model input parameters include dipole strength and the properties and geometry of the dipole, sea, and seabed system.  This computer model has been used by the Canadian navy for many years.  Furthermore, it has been incorporated into TMSS, the Total Mine Simulation System, to provide the electric and magnetic field signatures of a simulated ship.  TMSS is used by Canadian, US, UK, and Australian navies to simulate the encounter between a ship and a mine with various trigger sensors.

The Weaver model has been validated on many occasions.  In particular, in1996, Davis was involved in a NATO validation exercise in Halifax harbour.  During this exercise an underwater electric field range installed at a choke point was monitored and a video camera was installed in order to correlate ship signatures with actual ships.  The model parameters for a particular ship were estimated from its size and class and then adjusted so that the measured signature and the calculated one matched.  Thus, for example, a typical warship with hull coating in good condition, could be modeled with two dipoles, one from the rear ICCP anode to the propeller on each side.  To verify the predictions, several dipoles were towed behind a barge and the dipole parameters current, length, and depth were adjusted to mimic a particular ship signature.  In each case, the original ship’s signature and the signature measured from the dipole model of the ship, were the same.

The Davis software program, ShipEM, provides signature information which is crucial for designing ships and submarines.  ShipEM is based on the Weaver dipole model which calculates the electric and magnetic fields around a ship based on its dipole currents and geometry.  Knowledge of these electromagnetic fields allows the ship designer to minimize signature and, therefore, maximize survivability.

ShipEM is composed of a front-end to simplify the input of ship model data, the Weaver calculation engine, and a back-end to combine the results of multiple dipoles from a ship and provide graphical output.  It provides a three-dimensional view of the magnitudes of the electric and magnetic fields in the water around the ship.