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C's Skis - Easy to adjust (and extremely light weight) Fin Block

CsSkisCsSkis Posts: 120 Baller
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.
Chuck Illi
Chuck Illi


  • MattPMattP Posts: 6,092 Mega Baller
    @CsSkis Thanks for sharing.
    "I will be releasing info on my foray into converting a foam core waterski into a hollow one"
    Now this will be interesting.
  • jedgelljedgell Posts: 352 Baller
    Drill a couple holes, put in furnace, cook at 1000 degrees or so. The core will just flow out. Might want to take your bindings off first.
    Justin Edgell - Bozeman, MT
  • Than_BoganThan_Bogan Posts: 6,586 Mega Baller
    edited March 2013
    Some very elegant ideas here! It took me a bit to understand how you made the dft adjustment totally independent from the others, but now that I get it that's quite ingenious. The key is that you actually loosen the mounting screws so that the whole thing moves in dft (but everything else remains constant).

    How does the weight compare to other fin blocks?
    Nathaniel Bogan -- GUT Padawan
  • BraceMakerBraceMaker Posts: 4,136 Mega Baller
    @jedgell - depending on the core, acetone will dissolve lots of foam. It is a common way to laminate a plug then remove the foam by soaking in acetone.
  • bogboybogboy Posts: 699 Solid Baller
    We used acetone in j.h. Shop to bond plexiglass together, for making rings.
  • CsSkisCsSkis Posts: 120 Baller
    @Than_Bogan: Very light in comparison to anything I have previously encountered. I don't have any values to quote. (I guess I will have to get out my old postage scale!)

    @MattP, etc. With regard to the foam core waterski. No, I didn't melt it with heat, nor did I use acetone. Acetone will not attack a PVC foam core without also attacking the resin of the ski. Give me a day or two to write it up.
    Chuck Illi
  • MattPMattP Posts: 6,092 Mega Baller
    If @Horton reads these two threads I guarantee he will have traumatic flash backs to the Carbon Fin days....
  • HortonHorton Posts: 28,762 Administrator
    @MattP there is a small trickle of blood coming from my left ear
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  • MattPMattP Posts: 6,092 Mega Baller
    @Horton have a glass or two of Kilo Kai and try to forget it ever happened.
  • WaternutWaternut Posts: 1,511 Crazy Baller
    Cool concept and looks to be well made but I'm not sure I understand the point. My Radar fin blocks have been insanely easy to setup (put back to stock in my case). With all the set screws, you can make microadjustments easily or drop the whole fin out and put it right back in with very little difference if any. A friend of mine has a fin without the set screws and it takes him a while to make tiny changes.

    Regardless, it's good to see people proposing new ideas/concepts so don't take my criticism negatively.
  • MattPMattP Posts: 6,092 Mega Baller
    @waternut use a current O'Brien fin clamp and you will completely understand the design. 3 of my skis have O'Brien clamps and its somewhat of a pain to use sometimes. There are no set screws just two pieces that tighten together to hold the fin in place. The slot is usually very tight and to make minute adjustments it can take a while to get the settings right.
  • WaternutWaternut Posts: 1,511 Crazy Baller
    All of a sudden, I'm happy I've never owned one of those ski's.
  • MattPMattP Posts: 6,092 Mega Baller
    @waternut been missing out, don't bash it until you try it.

    @CsSkis I may be completely crazy, but could I not take two sets of wings and drill them out for this to work? Simple solution? I haven't done the measurements, but visually it look like it may work.
  • CsSkisCsSkis Posts: 120 Baller
    @Horton and @MattP: Yep, my wife couldn't understand why I wouldn't want to make and sell them myself. "Don't you want to make money?" All of the time I was thinking "Hmmm, Horton and Carbonfins".

    @MattP: I checked the wing idea you proposed. Unfortunately, there isn't enough wing material to work with to get the dimensions required. See my separate e-mail to you.
    Chuck Illi
  • MattPMattP Posts: 6,092 Mega Baller
    @CsSkis hey it was a shot in the dark, you never know!
  • Steven_HainesSteven_Haines Posts: 1,045 ★★★Triple Panda Award Recipient ★★★
    Now that D3 is making a big deal about the rocker of their Quest (wanna try one!) Did you notice any difference in your skis performance since your fin block idea doesn't limit flex as much as a typical block? Or is this designed more towards ease of adjustment? Very cool! I like it!
  • CsSkisCsSkis Posts: 120 Baller
    @Steven Haines: I'll paraphrase something that I said on the D3 Rockerblock thread. If your ski is flexing significantly in the last 8 -10 inches, I would be very worried. In order for that section of the ski to flex, the carbon laminates would have to be extremely thin, and it would have to be the top sheet that was providing the "give" in compression. So, no, I didn't construct the fin block to preserve flex. The motivating factors were the ease of adjustment, simplicity and light weight.
    Chuck Illi
  • Steven_HainesSteven_Haines Posts: 1,045 ★★★Triple Panda Award Recipient ★★★
    Cool! Thanks for the explanation! Pretty ingenious tho
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