If budget wasn't an issue.

http://kayak.co.za/the-kayak-shop/kaskazi-kayaks/kaskazi-dorado/

While efficiency of the Kayak is very important and contributes to speed of the Kayak, I am assuming that efficiency is greatly enhanced with the addition of a rudder. All the pedal driven kayaks have rudders, so I should plan on adding a rudder to the paddle kayak. Would adding a rudder to the Tarpon 140 and Ultra 4.3/Trident 13 significantly improve the efficiency of the kayak?

Sorry for all the questions, The Aggie in me

Found a Trident 15 closeout w/o rudder at clearance price of $899.00 with rudder $1099. Trident 13 Blemish for $899.00 w/o rudder.

Good Deal?

On the contrary, rudders add drag and slow a kayak down.

The Hobies' need a rudder with their pedal system because they no other way to turn. A rudder is nice for fishing because they allow you make minor adjustments while drift fishing. They also help if you're paddling into a crosswind or diagonally to keep the kayak pointed where you want it to go. Typically, a longer kayak is needed to help turn it in tighter quarters than for tracking reasons.

The Trident 15 looks like a good deal, the 13 not as much.

So the Trident 15 would be a good candidate for a rudder whereas the Trident 13 and tarpon 140 would be ok without. How much faster is trident 15 over 13? Trident 15 has molded foot pedals, Trident 13 adjustable foot pads. Molded foot wells seem it might interfere with adding a rudder. Tarpon on other hand more open deck space

Well... I'll defer to Neumie about the rudders, their drag, and the effect they have on the absolute speed and efficiency of the yak, but I have one on the T140 and really where it makes a difference for me is when I want to take a line across a water body with a stiff cross wind... It keeps the bow on point and makes for a MUCH more efficient trajectory. If you're trying to paddle due north in a 22 mph east wind, the rudder really limits the amount of correction you need to make it from point A to B... GIGANTIC difference for me personally... Controlling a drift is nice too, but the biggest pro for a rudder in my personal experience is this ability to hold a course in a big cross or quartering wind. That rudder might be producing drag and lowering my top end speed, but I'm getting to where I want to be much faster and with a lot less effort without all that paddle correction...

The exact time was 30min 11 sec.

I have real doubts about a 6 mph average over 5000 meters by anyone. Not taking anything away from Christian or his kayak as he has the reputation for moving it fast, but I believe someone screwed the pooch when they measured the course or misread the clock. Ain't no kayak that any of us fish out of that can keep that top end speed for that long...bar none.