The Nomad is a sea kayak, not a surf ski. So my plan is to make a rectangular stern mounted flip-rudder (Is that the right name?) like the SmartTrack or Feathercraft rudder. They are just mounted with a bolt through the pivot point, so I guess they are easy to replace. Rectangular rudders are probably also easier to construct than elliptical rudders.

I tried to put the picture of your rudder into Sketchup and scaled it to fit the Measurements. It has an area about 188-214 cm2 (very very approximate - I tried to scale to both the vertical and horizontal dimensions). That is 3.2-3.6% of the Nomads lateral area.

I have also tried to calculate how this area relates to your Think EZE. I can't find any info about the LWL and draft, but the total length is 520 cm. But since it has almost vertical ends I guess it's more or less the same as the Nomad (528 cm).

I have read that your Panthera is 5.6 m LOA. I can't find any LWL or draft, but I am assuming the lateral area is around 6050-6720 cm2 (The ends are almost vertical (LWL=550-560 cm)and most of Björns other designs has a draft around 11-12 cm). So the SmartTrack rudder is 2.3-2.6 % of that. Nice kayak.

To summarize my calculations:

Nomad with SmartTrack rudder: 2.75%
Nomad with Think EZE surf ski rudder: 3.2-3.6%
Panthera with SmartTrack rudder: 2.3-2.6 %
Think EZE surf ski: 3.2-3.6 %

Average: 2.8-3.1%. I will let that be the conclusion of my rudder area issue. Unless someone has other comments.

Now I just need to find the best aspect ratio. (Relationship between the width and length of the rudder)

Palle