A longer base length results in more water engaging fin at the joint where it meets the surfboard. The J Drive fin system has increased that base length so much that it is actually larger than the depth of the fin. Something rarely if ever seen with surfboard fins. The length of the base affects forward drive. More length equals more drive but typically this comes at the cost of things like maneuverability and looseness. The second noticeable difference in the J Drive fin is the cut away section. This feature allows the fin system to maintain its increased base length while minimizing surface area. This helps ensure that there is not an excessive amount of hold coming from the fins. The bigger the surface area of your fin, the more hold you will have but if you have too much you will not be able to release from turns and make use of your drive power.
 
Solid Fiberglass
Center Fin
 
5.0"
Base      5.0"
Height  5.0" 
Foil      Double
 
5.5"
Base 6"
Height 5.5"
Foil Double
 
Fin screw and plate included