Sorry for the long discourse, but I wanted to be somewhat complete in the description.
I'm not selling fin blocks, I'm just offering the design if someone wants to replicate it. I have been doing personal R&D for a number of years now and I'm starting to "divest" myself of some of my waterskiing related ideas that have passed their field trials. Similar info will be released on a simple change to waterski gloves that was able to reduce/eliminate the potential for sore hands and ripped calluses. In addition, for fun, I will be releasing info on my foray into converting a foam core waterski into a hollow one, and my saga of developing various (unusual) waterski binding solutions.
With regard to this fin block, it has been in use for several years on several different skis (Refer to first photo) and tried by different people in the industry. The fin settings, once set, have been totally stable. And, as discussed in the D3 Rockerblock thread, the fin block will not change any existing tail rocker of a ski.
The driving force behind the creation of this particular fin block (more of a clamp, really), was the frustration with the, sometimes interminable, length of time it took to adjust a "conventional" fin block (think O'Brien/Elite). Typically, I would get one adjustment made and then it would have caused something else to change. After multiple iterations, I might get the setting I was targeting. So, I looked at what was out there, and what had been used in the past, and created what you see in the attached pictures. It separates DFT from Depth and Length and, more importantly, minimizes the changes between Depth and Length when these settings are changed - therefore, fewer iterations. I am able to set up a ski, from scratch, in approximately 10 minutes with this fin block (and that includes mounting it to the ski blank) It can take less than 5 minutes to make a small adjustment. (About 1 minute, if it is just DFT.)
The key to the fin block, other than it being simple and very light, is the slots used in the clamp (for DFT adjustments) and in the fin itself (for Length and Depth adjustments). (Refer to second photo for disassembled fin block) - The slots are cut in a manner to be just a few thousandths larger than the 8/32" NC machine screws clamping the fin and fin block. I decided to cut the slots just long enough to accomodate the typical adjustment range. But, this is not critical to its purpose.
The other important design element is the location of the aft-most slot in the fin blade. It is located such that the fin will pivot in an arc (where the radial begins in the center of the aft fin slot (Refer to third photo), that is very close to the arc/curvature of the bottom of the fin blade in this vertical location. This allows the Depth to be minimally or totally unchanged when adjusting Length. The forward most slot location is somewhat arbitrary. In this case, it allowed me to machine all four fin clamp pieces to be the same (other than being mirrored).
The upper exposed part of the leading and trailing edge of the fin is only slightly higher than what occurs with the same fin setting in a conventional O'Brien/Elite fin block. In addition, there are no sharp or 90 degree edges with any of the components (it might not look that way in the pics). I agree that there is a lot more "blade" exposed in the center section, but I would speculate that there are very few people who have been whacked by that part of their ski. In addition, it is no more sharp than the fin itself!
The shape of the fin clamp parts shown in the pictures are specific to the insert pattern of an O'Brien/Elite fin block. Ideally, new insert locations would be specified if this fin clamp were to be installed as standard. (I created a differently spaced, and more efficient, fin clamp that was installed on a ski that did not have inserts. The fin clamp is not shown, as it was given to Eddie Roberts for a separate evaluation.)
Adjustment process (new fin and clamp):
a) With fin block assembled, insert fin into ski and finger tighten all screws
b) Set DFT to match approximate final number (again, the screws only need to finger tight)
c) Set Length to match approximate final numbers (screws only finger tight)
d) Set Depth to match final number and lightly tighten screw with allen wrench
e) Set Length to match final number and tighten both front and back fin-to-clamp screws with allen wrench
f) Set DFT to match final number and tighten fin clamp-to-ski screws with allen wrench
g) Check measurements - If all are correct, ensure that all screws are tight
Adjustment process (for small adjustments):
h) If it is just a DFT change, then conduct Step (f) after loosening clamp-to-ski screws
i) If it is just a Length change, loosen front fin-to-clamp screw and lightly loosen rear fin-to-clamp screw. Rotate fin to adjust length (if you are careful, the Depth should not change) and tighten screws.
j) If it is just a Depth change, loosen rear fin-to-clamp screw and lightly loosen front fin-to-clamp screw. Rotate fin to adjust Depth and tighten screws. Note: There is a possibility that the fin Length will slightly change when changing Depth. Some iteration on (i) may be required. (An increase in Depth may very slightly shorten Length, and a reduction in Depth may very slightly increase Length)
It should be noted that the modification was accomplished using an O'Brien/Elite fin blank. Examination of the current RADAR fin blank, for example, reveals that the modification can't be accomplished as there is no fin material at the desired rear adjustment slot location. In this case, a new fin blank would need to be "cut" to replicate the RADAR fin shape and "ventilation" hole pattern.
If you have any questions, just ask.