It is impossible to ensure that the marine streamer shall strictly follow the line of profile (containing the shotpoints) in marine data acquisition surveys. In fact it rarely does so. Deviations of the streamer from the line of profile are termed "feathering" which can vary from a few degrees to 30 degrees or more, depending on sea conditions. Feathered marine data are not quite suitable for conventional velocity analysis for stacking purposes. Errors introduced in the use of conventional analysis are addressed and an accurate velocity analysis approach is suggested.