Construction of Breakwater requires large volumes of appropriately graded rock. Geological characteristics and blasting practices at the quarry determine the gradation of the quarried rock. If the gradation of quarried rock does not meet design requirements, there is wastage of quarried rock or additional cost to reprocess it to meet requirements. This work utilizes mathematical models to forecast the gradation of rock from primary blasting. These models are programmed in the form of a spreadsheet to be used for decision support. By varying the blasting parameters the best fit between requirements and quarry yield can be found. In addition, a genetic algorithm based optimization model to determine the optimal values is also developed and illustrated with an example.