This is from ABT's website:
TRAC stabilizer fins and exclusive winglets are computer-optimized to provide the highest lift-to-drag ratio available. Fins are built to exacting standards using modern vacuum-infusion methods, GRP laminates, and structural foam cores. TRAC fins are free-flooding and near neutrally buoyant, reducing overall weight. The TRAC winglets create an "end-plate" at the tip of the fin to prevent the escape of water from the high-pressure side of the fin to the low-pressure side. This increases the overall efficiency of the fin and provides more anti-roll force than conventional offerings. The TRAC winglet also significantly reduces drag creating "tip vortex". TRAC fins and actuators are selected (sized) based on specifics of the vessel hull, roll period, speed range, and meta-centric roll radius.