Off-vessel treatment of ship-generated waste is one of the ways to ensure environmental safety in ship operation. Sewage and oily waters generated on the vessel are transferred to coastal environmental protection facilities with the help of a collecting vessel. When considering such a way of ensuring the environmental safety of shipping, a number of issues arise related to the optimization of the operation of such a system. In this article, the influence of the average speed of the collecting vessel on the operation of the off-ship waste collection system is considered. To solve this problem, a numerical model of this system was developed, that combines elements of probabilistic and simulation modeling. There was found to be a negligible effect of the speed of the collecting vessel on the performance of this system. As a result of modeling the operation of the ship waste collection system through the collection vessel, it can be said that high speeds of the collecting vessel are not required in ship maintenance.