As it is known, to provide fire protection for any type of surface vessel, external fire-fighting (EFF) systems have been commonly used for decades as well as in coastal regions. These types of systems exist on several types of vessels such as fire-fighting ships, tugboats, supply vessels and naval vessels. Flow conditioners can be used in the EFF systems to provide better performance by regulating the flow inside the fi-fi monitor. In the present study, a fire-fighting (fi-fi) monitor was designed and different flow conditioners were implemented into the fi-fi monitor. A unique flow conditioner was designed in addition to the recommended ones by ISO 5167-3 in order to improve the performance of the flow conditioner in terms of head ratio and flow rate. A commercial computational fluid dynamics (CFD) solver was used to investigate the performance of the different flow conditioners. Before comparing the numerical results of different flow conditioners, the numerical model was validated with the experimental data and verified with appropriate methods. The results showed that the unique flow conditioner successfully regulates the streamlines and it has better performance than the recommended ones by ISO 5167-3 in terms of flow rate and head ratio. As the last part of the study, the effect of unique flow conditioner length was investigated and the best length was determined.