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 Post subject: Turbofin test II
PostPosted: Wed May 03, 2006 11:44 pm 
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Joined: Sat Nov 12, 2005 10:46 pm
Posts: 2408
Location: Escondido
Amsurferoceanbeach and OffRoad posted some excellent observations on the new Turbofins. I also tried mine today and would like to add a few notes (also in the Adventure). I found the new fins to be both more efficient and faster.

Crusing along with normal effort, the cadence was slower and the speed was 1/4 to 1/2 mph faster. Whereas normally I can sustain about 3 1/4 mph on the pitot tube speedometer*, the Turbofins gave me about 3 1/2* to 3 3/4* mph. Not a bad increase -- 10%+/-! The new fins are hydrodynamically superior to the old fins, so this is not a surprise.

Top speed was also higher with the Turbos. With the standard fins I could get about 5 1/2* on the tube. The Turbos got up to 6* mph before I passed out (just kidding -- I could have held it for another second at least, maybe!). Again, a 10% improvement.

Obviously, the Turbos can accelerate faster than the standard fins. Using the large rudder, I found the turn radius measured to be mostly identical but perhaps a little tighter with the fins resting in the vertical position (acting as a fulcrum). Regardless of fins, the large rudder makes a big improvement in the turning and manuverability of the hull!

One of my specific objectives was to look at the sustained effort to operate the Turbos. I agree with OffRoad that these fins are not for everybody, but not for the same reason. Anyone who is happy with the standard fins would have little to gain by upgrading. Similarly, anybody who can not operate the standard fins continuously would be wasting their money on the Turbofins. But in my opinion, the Turbos are no more difficult to operate if you run them at a slower cadence. I found tham very relaxing and easy on the muscles and joints, once settling into their pace.

Overall, the Turbos are a nice alternative for those who want more performance from their Hobies. They clearly extend the capabilities of the Mirage drive. I'll definitely be keeping mine!8)

* Previous runs with the GPS indicate 1.1 mph faster than the tube indicates (in my case with the Adventure). This is not a universal correction factor.


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PostPosted: Mon May 08, 2006 12:19 am 
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Joined: Sat Nov 12, 2005 10:46 pm
Posts: 2408
Location: Escondido
Had an excellent session with the new fins today. :D 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!" :lol:

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. 8)


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