There's the sport rudder and the elliptical rudder.
The sport rudder is smaller and produces less rolling moment i.e. it doesn't turn the boat as fast but the benefit is that the boat feels more stable.
The elliptical rudder is larger and makes the boat turn faster but it also induces a stronger rolling moment when you turn and this makes the boat feel less stable.
If you're a beginner, it's best to start with the sport rudder, but if you get to the point where you're doing downwind runs in big conditions, you'll definitely want the improved maneuverability that the elliptical rudder brings.
The rudders are reasonably easy to change with the aid of an allan key.
Rob
Currently Epic V10 Elite, Epic V10 Double.
Previously: Swordfish S, Evo II, Carbonology Zest, Fenn Swordfish, Epic V10, Fenn Elite, Red7 Surf70 Pro, Epic V10 Sport, Genius Blu, Kayak Centre Zeplin, Fenn Mako6, Custom Kayaks ICON, Brian's Kayaks Molokai, Brian's Kayaks Wedge and several others...
