Fairings are devices that surround a tubular and streamline the flow so that only small vortices are shed at the fairing tips. Fairings still shed a large amount of vorticity (just like a bare tubular) but the forces on the underlying tubular are relatively small, both locally and globally. Typically fairings are designed to rotate around the tubular so that they are free to weathervane with changes in the oncoming current direction. If they fairings are locked to the tubular and not free to rotate, they can still effectively suppress VIV (depending upon the fairing design and the relative angle of the oncoming current and the fairing chord) but will usually experience a higher mean drag force as well as a steady lift force.
Not all fairings are equal. Fairing performance can be dependent upon the fairing chord (the distance from the fairing nose to the fairing tail), the fairing thickness, the Reynolds number, surface roughness, the shape of the fairing side walls, the shape of the fairing tail, the annulus between the fairing and the tubular, etc.
Because fairings streamline the flow similar to an airplane wing, effective fairings produce substantially lower drag than do helical strakes. Fairings are also less sensitive to soft marine growth on their surface than are helical strakes, and fairings usually produce lower motions on downstream tubulars than do helical strakes. While fairing drag coefficient depends on the fairing geometry, the Reynolds number, and a few other variables, it is possible to design fairings with drag coefficients less than about 1.0 for a production riser and in the range of 0.6 or less for a drilling riser.
While fairings, like helical strakes, can experience substantially reduced effectiveness due to the presence of hard, barnacle type, marine growth, tests have shown that soft marine growth can be well tolerated by fairings with sometimes a negligible reduction in the fairing performance. While it is possible to apply to fairings the same anti-fouling coatings that are applied to helical strakes, it is most important for fairings that the bearing surface between a fairing and adjacent fairings or thrust collars is kept relatively free of marine growth so that the fairing can properly weathervane. VIV Solutions offers copper protected collars that reduce, or eliminate, marine growth restrictions on fairing rotation.
Fairings can be very effective at reducing VIV and produce additional damping for the tubular to which they are applied. This damping can further reduce the motion of the underlying tubular.
Fairings can be pre-installed or installed via reel-lay, j-lay or s-lay in very quick fashion. Fairings can also be retrofit by diver or ROV. For drilling risers, VIV Solutions offers special fairings known as Tail FairingsTM that aid in the installation due to the large diameters associated with drilling riser buoyancy.