fin tuning (again) how does holes affect the ski ?

[sfriis]

Im currently on a new Arc (blue) and tested it with an old D3 fin

 

as you can see there are some more holes (for another wing) at the bottom... can I expect different behavior when mounting the factory fin ?

 

The ski is perfect now so I don't want to experiment too much...

 

(new) factory fin:

 

 

 

 

 

 

 

 

[LeonL]

I guess I'd have to ask why you first went with another first instead of what was in it? My impression of additional holes would allow the ski to smear a bit more. Maybe @SkiJay will,comment on this for you.

[sfriis]

I started out with a demo, my friend changed the fin to save the factory fin - we ski in a very shallow lake (sometimes scraping the fin).... Maybe I will just keep this fin.

 

I also would expect slightly more smear - perhaps more drag ?

 

I guess I will have to try it out - maybe @skijay can suggest how to compensate ?

[SkiJay]

Hi @sfriis. When D3 first made the switch to the new fin, I wrote this report on the difference: goo.gl/nsfKJC

 

For the most part, the difference is small enough to ignore unless you are skiing every day. The old fin smears just a tiny bit more, both because of the extra holes and because of the extra flex of the new fin. But you may like the extra smear.

[sfriis]

wow fantastic service @SkiJay thanks

[DW]

@sfriss: the 'extra holes' were there to allow multiple wing mounting positions. Lower & rearward variations from the typical standard wing mounting location. Looks like two thickness variations available on the new fin from D3.

[aupatking]

buy "fin whispering". I did, it's worth it.

[sfriis]

@DW yes I know why they had the extra holes, I just wanted to know if anyone could tell the difference on the ski and how to "correct", SkiJay have tested the 2 fins on the same ski and have described the difference in his old report - exactly what I needed to know.

 

@aupatking - Yes I will :)

[DW]

@sfriis : I am using one on a Goode and it works very well, as SkiJay noted, a very subtle difference from a conventional style fin w/o the extra holes. I feel there is slightly less roll resistance but very minor. I was expecting or wondering if the extra holes would lead to a potential easier tail blow out scenario, I did add .010" in depth to compensate and that seems to be working for me.

[sfriis]

OK tried both fins and must say that not much difference BUT i had to ski with much different "settings" on the new fin - i think it is because the edge/front of the new fin is a tiny bit "longer" right where you measure the length - so in order to have both fins settings equal I had to go up to 6,97 in length (factory = 6,930) - and funny enough - both fins now aligns the same (marks on fin aligns with the edge on both fins) - I think @SkiJay mention somewhere to be carefull not to scratch the front of the fin because even small scratces here can have a big effect on the FL measures (so FL is very sensitive).

 

 

[DW]

@sfriis : I would trust my caliper measurements rather than markings stenciled on the fin as there is probably some variation fin to fin on exact placement of marks. They are fine for reference marks on that particular fin IMO. You could measure the marks relative to the bottom edge of the fin to see if they are consistent fin to fin. Bottom line, if it skis well, that is what you are after:)

[SkiJay]

@sfriis @DW is right. Forget about where the holes or index markings are. To compare apples to apples, you need FD, FL, and DFT to be the exact same measurements to within .001" to .002" if not .0005". And these measurements need to be the numbers you end up with AFTER the fin block has been tightened. I know; picky, picky, picky ...

[BraceMaker]

@SkiJay to compare apples to drill bits. Fin dialed in.

 

What happens if you take and nascar drill the fin. For instance increasing the size of each of those holes 1/8". Obviously FD,FL,DFT are the same - fin surface area decreases.

 

Impact?

[Horton]

Extra holes also equate to additional turbulence which equates to drag which equates to stability.

[SkiJay]

@BraceMaker This isn't something I've tried. But my guess would be like you say, an effective reduction of fin area that would both reduce roll resistance and increase smear. Steve Shnitzer wrote about how even countersinking the relief holes will affect ski behavior. Personally, I think you can do whatever you want to your fin, but it all comes back to how much tip-engagement you get from your ingrained habits, and how much the ski smears. So even if a fin is full of holes, LE and DFT will simply change until you're right back to predictable behavior with a good tip-to-tail balance.

 

I love this picture of the fin Chet Raley was using a few years back. Notice how far back the fin is in the fin slot. This suggests that a lot of holes made the ski smear more so a much shorter DFT was needed.

 

 

[dwfrech]

I was wondering about this ... how do you decide where to put the wing? It can be significantly higher (closer to bottom of the ski) or lower, even at the same angle relative to the tangent line to bottom of the ski under the fin block. I don't know what it does to have it higher or lower, and I'm not sure if there are specifications about that setting (though there are somewhat standard recommendations for fin angle). Also, you could mount the fin upside down (wing on bottom) or the other way (wing on top of the clamping part). I have no idea and don't do much with it because I don't know what it does. Any help .... thanks.

[SkiJay]

@dwfrech The higher set of holes add the most drag (due to extra turbulence caused by the wing's close proximity to the ski's base and water's incompressibility). And there is still a lot of drag during acceleration. The "normal" location creates less overall drag. But more significantly, drag is lower during acceleration than it is during deceleration as the wing's effective angle of attack changes with the ski's tip attitude. The lowest placement creates the same reduction in drag during acceleration as the "normal" position, but tends to pitch a little more tip into the water—a somewhat temporary effect subject to skier adaptation. It also places the wing too far from the ski's base to be conveniently measured by most wing gauges and makes so little difference that it's not worth the hassle.

[sfriis]

@SkiJay - yes I know that you have to compare FD,FL,DFT and not the marks on the fin - however I notice that the 2 fins are not exactely the same - and strangely enough I feel the ski act the same when I align the markings - which make a huge difference in FL : I now ski FL 6,97 (feels like the old (slightly different) fin on 6,930) and the ski works perfect - new PB yesterday for the first time in 25 years - Im happy - love the new blue ARC.

[SkiJay]

Sorry @sfriis, I misunderstood. Big congratulations on the PB!

[sfriis]

@skijay thanks - and I apreciate your comments - learning a lot from you - I Will try to buy Ur book in Spain at the WC +35 this weekend or order a copy when back :)