While theoretical VIV analyses often assume that each tubular joint can be fully covered with VIV suppression, many tubulars have connectors, anodes, and other appurtenances that prevent 100% coverage.
Fortunately, most of the joint length can be sufficiently covered to achieve an overall suppression effectiveness that approaches (but still fall short of) that of full coverage. For helical strakes, it is suggested that a minimum of 85% of each joint be covered with well-designed helical strakes. Use of properly-designed fairings on a minimum of 70-75% of each joint can, in many instances, approach the effectiveness that would be achieved by covering 100% of the joint length. A key element is to provide sufficient coverage density such that all possible anti-nodes of vibration are accounted for.
Another key element is to impose enough damping in the tubular system to reduce, or eliminate standing waves (though traveling waves can still cause substantial fatigue damage). Of course it is also important to cover areas that experience significant currents and to ensure that the overall riser coverage is sufficient.
Installation of suppression along a particular section of riser can have a positive impact upon the entire tubular. For example, Tail FairingsTM are commonly installed on drilling risers just below the water line and extend downward to a point at which surface currents subside. Not only do the fairings reduce VIV here, but they also introduce some additional damping all the way to the wellhead. Fairings are known to add more damping than helical strakes, but both devices usually add more damping than that produced by the bare tubular.