1. A computer application stored on a computer-readable storage medium for the optimization of marine transportation scheduling comprising: code that, when executed, calculates the optimal solution to maximize total net margin for the assignment of vessels in an available fleet to perform a set of voyages to be initiated during a planning period for transporting cargo comprising one or more bulk products, where the total net margin is derived from individual net margins for each vessel/voyage assignment and each individual net margin for a vessel/voyage assignment is derived from the market value for the voyage using market freight rates and a predicted incurred cost for the voyage using the assigned vessel, and where the code includes at least one linear programming portion and at least one mixed integer (linear) programming portion; where the fleet of vessels comprises term vessels and spot vessels and where term vessels can be assigned to multiple voyages within the planning period, where the application determines each feasible vessel/voyage assignment, given temporal and physical vessel and voyage constraints, and then calculates individual net margins for each feasible vessel/voyage assignment using the formula: 
 NM=MV−IC where “NM” is the net margin for the feasible voyage/vessel assignment, “MV” is the estimated market value of the voyage based, at least in part, on market freight rates, and “IC” is the predicted incurred cost of the voyage using the assigned vessel, where the estimated market value for each feasible term vessel/voyage assignment considered by the application is determined by the following formula: 
 MV TERM =[FR*(WS MARKET /100)* C ]+CT UNDIS +DC IDEAL +NHV where “MV TERM ” is the estimated market value for the voyage using the term vessel “FR” is the voyage flat rate, WS MARKET is the market Worldscale rate expressed as a percentage, “C” is the maximum total tons of cargo that the term vessel can carry without violating vessel and/or port constraints for the voyage, “CT UNDIS ” is the applicable laden and/or ballast voyage canal tolls for the voyage and a reference spot vessel, “DC IDEAL ” is the market demurrage cost for the voyage assuming a best case scenario where a vessel incurs no demurrage costs waiting ahead of the supply dates at the first supply location in the loading segment of the voyage, and “NHV” is a net hire value assigned to a term vessel that performs the voyage and is calculated using a daily rate for each day the term vessel is available after the term vessel has completed its assigned voyages for the planning period and a specified start date for incurring the daily rate has been reached, with the daily rate continuing until a specified end date.