Commercial towboats in navigable waterways, particularly in confined reaches, generate waves and currents which can be of significant magnitude such that stabilization of the banks with riprap is warranted. This paper focuses on stable riprap design for tows under way (here referring to those whose sailing line is parallel to the banks and whose speed is constant). Therefore, return current, wave characteristics, and channel geometry are the governing parameters for sizing the stone. Propeller jet impacts due to maneuvering tows are not addressed. Most of the existing guidance on sizing the riprap on the banks for waves has been based on coastal waves. The riprap design guidance pertaining to waves produced by typical commercial towboats found on US waterways is limited. Based on site-specific needs to address stone sizes due to towboat-induced forces, several studies have been conducted at the US Army Engineer Waterways Experiment Station (WES), Vicksburg, Mississippi. The physical model studies include the Tennessee-Tombigbee Waterway, the Gallipolis Lock approach on the Ohio River, and some general navigation research regarding stone slope stability in confined waterways. Although these studies have been primarily devoted to the evaluation of specific stone sizes and gradations subjected to specific towboat operations, the study results lend themselves to use as general riprap design guidance. The underway tow studies have dealt with quantification of return currents and the magnitude and characteristics of secondary and transverse stern waves in lock approaches and confined channels. While current research at WES is ultimately aimed at verification or modification of existing riprap design equations which incorporate tow-induced forces, the results to date have led to somewhat more qualitative conclusions regarding the stability of particular stone sizes subjected to tow-induced forces. This paper summarizes the physical model test conditions, makes recommendations for the stable rock size, compares these results to existing riprap design equations, and presents the limitations to which these recommendations are applicable.