Had an excellent session with the new fins today.
Here's what happened.
At the local lake, it's about 2.4 miles from the launch ramp to the dam. My previous best time (small fins) = 32 minutes no wind (4.5 mph average). With the Turbofins this morning, 28 minutes (5 mph) with 8 to 10 kt. headwind (fairly flat seas). Then I returned within the same time (no headwind, but slightly easier pace). This works out to a 12.5% increase in speed for an extended run. This is huge, remembering that going from 4.5 to 5 mph increases drag by almost 50%!
I could still bump it up to 5.5 mph for a short time and recover at the original pace.
I had the fins tightened to the max. On a speed run, I only got to 5.7 on the tube (about 7+/- actual). So in the afternoon, I went back and experimented with the tightening knob. At full slack, I suffered no loss in speed, but it seemed
to take more work to maintain a midrange speed. Next I tightened to a middle position (rear of fins about 1/8" in the groove). Much better midrange performance, good acceleration and 6.2 on the tube (about 7.5+/- actual) for a speed run (mostly calm, flat seas). So far, this appears to be an optimal position for the fins. Next opportunity I'll try an extended run in this position.
The moment of the day -- I picked up a nice swell (fresh boat wake) pegging the tube out at 7mph for about 30 seconds. Wild ride! Once again, big rudder, big fins = new horizons!
Getting accustomed to the Turbofins, they are starting to feel quite normal. It still seems impressive that one can get a nice pace with a very leisurely pedaling speed. It gives a sense of power. "Look, up in the sky, it's a bird, it's a plane, its -- superyak!"
Finally, I did some more calibrations of the tube with the GPS. For the Adventure (+ 180 lbs), 2.5 indicated = 3.5 actual; 3 indicated = 4.1 actual; 3.5 indicated = 4.7 indicated; 3.75 indicated = 5 actual. These notes are good for me because I don't like to carry the GPS around all the time. Additionally, the tube is easier to read w/o glasses, it doesn't lag and it reports actual water speeds (ignoring currents) for more accurate testing.