All Hobie accessory products ship for a flat rate of 7.99 and cannot be combined with other items to receive free shipping. Designed to increase speed! Hobie Mirage kayak users report as much as 10% increase in speed and more using ST TURBO Fins. But its not all about speed, you can get top end speed and a slower cadence for cruising Less pedals per mile. All achieved with these larger and more efficient fin designs. The longer fins can also increase lateral resistance for sailing upwind. These ST Square Tip designs will require a bit more effort to pedal. The added effort is commonly compared to pedaling a bike up a slight incline. In addition, the included fin tension screw allows adjustment to achieve lower end torque or top end speed to meet the desires of the pedaler. Includes two fins and two masts. Purchase 2 sets to retrofit a tandem kayak.