I recently got a new set of Turbofins and noticed some subtle changes from my older ones. I already posted on this, but have taken some pictures for clarification. Note, all these changes may not have occurred at the same time, so you may have any combination of these changes.
In this first picture, the newest components are on the top and the older ones are on the bottom.
The first thing you notice is the shorter mast. The new one is 13 15/16" long and the older one is 14 3/16". This loss of 1/4" allows the fin to tuck into the sprocket guard slots for a closer fit.
The second thing you can see is the larger chain notch on the newer fin.
Finally, on the right side of the picture, you'll notice the fin is now pinned in place at the clew (using your original clevis pins) instead of screwed in. This prevents over-tightening and resulting loss of performance and clew adjustment problems. Note the two different pin/screw lengths: short for the newer drive style and longer for the older drive style.
These next two pics detail the changes in the fins. They are identical except for the larger notch and the larger hole for the clew adjusting screw (to accommodate the clevis pin). As you can see, the clevis pin cannot be used with the old clew adjusting screw.

In this last picture, note the difference in mounting. The new fin sits on the left and the older fin is mounted on the right. The latest fit is more snugged up and has a more integrated appearance.
Originally there were four ways to screw up the mounting of your Turbofins: 1) over-tighten the clew mount so the out-haul could not rotate; 2) use the wrong screw on the old drives; 3) over-tighten the mast mount Allen-head screw, thus weakening the mast mount; and 4) fail to seat the mast fully and pointed in the right direction. With the latest changes, you can't commit error #1or 2, so reliability of the fins should be improved.
If you happen to have the shorter masts but the older fins and the notch is causing a problem, you can either trim the fin (haven't tried it) or add a 1/4" dowel plug to drop in the fin mast hole before you mount it (have tried it).
Its nice the way Hobie continues improving their products, even the smallest details!
