Embodiments disclosed herein describe cylindrical structures with indents configured to reduce vortex induced vibrations (VIV). For example, the cylindrical structures may be configured to reduce VIV for drilling risers subject to ocean currents. In embodiments, the indents may be positioned on an outer surface of the cylindrical structures, wherein the indents may be parallel pairs. The pairs may be mirrored between a first end and a second end of the cylindrical structure, and be positioned in a helical pattern, which may be continuous or staggered.

A marine drilling riser protection system including a plurality of protection modules adapted for fitment at spaced intervals along the length of a riser, and a plurality of cover parts, wherein each cover part is adapted to be fitted at one end of the cover part to a first protection module, and at an opposite end of the cover part to a second protection module.