How can .001" or even .005" make a difference?

[Slalom.Steve]

First a quick clear-cut question: when making fin adjustments to the thousandths, is it only ever in increments of .005" (so the final measurement ends up at .xx0" or .xx5"), or are there people ending up with measurements like .xx3"?

 

Then the real question: I am fairly new to course skiing, and have yet to learn much about fin adjustments, but I certainly plan to, as I really like the gear/tech side of things.

But I have to confess: I don't understand how moving a fin .001" or even .005" could make a difference in performance. An average human hair is about .003." So we're talking an adjustment of roughly the width of a single strand of hair… intuitively, it just doesn't make sense to me.

 

I am curious to hear people's subjective opinions, but most especially if there's any definitive "lab testing" that shows what difference, if any, can come from such a tiny adjustment. And maybe a scientific explanation to replace my unscientific intuition of how that's possible.

 

Thanks!

[kurtis500]

 

 

[Than_Bogan]

To my intuition, it makes no sense that even 5 hundreths would really matter, but all you have to do is try that with a standard fin, and you'll see it dramatically changes your ski -- may even render it almost unskiable.

 

But does a thousandth really matter? That's less clear. I am pretty confident that 1/10,000th can't matter, because the expansion of 7" of aluminum under a few degrees temp change is on that order of magnitude.

 

So somewhere between 1/20" and 1/10000" there is a cutoff of what actually matters. My personal experience suggests that if I get within 1/200" (i.e. 0.005") of a previous measurement the ski will feel basically the same. But a full hundredth off might not quite feel the same.

 

Some princesses may be able to sense smaller peas, if you will.

[Horton]

@SlalomSteve

 

That is a great question.

 

First of all - if you are new to the course you want to find someone with experience to set your fin & binding to stock and then you want to walk away. Skiers who treat ski set up as a hobby or obsession almost always handicap their progress as skiers.

 

To the crux of your question.

The truth does not make any sense and I have spent more than a few hours trying to understand how it could be true. I challenge anyone to really explain how it can be true.

 

Yes .005” can be a big adjustment. .005 in depth or DFT can be the difference between an average setup and a great one. .001? Meh. .010 can be HUGE a huge change. Fin lenght is less sensitive but still very important.

 

I say “can be” because it depends on from where to where you are moving the fin. If the settings are already in a zone of great stability then it may be less sensitive. It also depends on the ski. Some skis are going to be more sensitive than others.

 

[jjackkrash]

The numbers drive me nuts because I personally don't trust the accuracy of the measurements down to .001 even with the best calipers, at least not when I'm the guy taking the measurements.

[Horton]

@SlalomSteve

You are a musician right? When you tune a guitar how many degrees of a turn on the tuning peg between in and out of tune?

[Than_Bogan]

@jjackkrash Sweating about a thousandth is almost surely a waste of time -- especially if you don't want to in the first place!

 

Side note: The repeatability with a good caliper and a consistent methodology can get pretty close to 0.001". Accuracy is doubtful at that level, but you mostly want to compare against your own measurements with the same caliper and same methodology, so repeatability is more important than absolutely accuracy.

[jjackkrash]

At Than_Bogan I think I am getting fairly proficient at repeatability and I don't sweat a .001" variance, but like its point out in the Fin Whispering book the jaws on the caliper themselves cut into the fin if you are not extremely careful and its very difficult to get consistent measurements without some modest pressure on the calipers. Little variances like this add up in a hurry when we are talking about .001-.005.

[Bruce_Butterfield]

Does a few thousands make a difference in how a ski performs? Absolutely. Better or worse is the big question. You have to keep in mind the things that are "different" in our day to day skiing. For starters:

 

different lakes ski differently

different boat/engine/ZO

different rope

different driver

different wind conditions

 

IMHO, the "difference" in the above on how a sker performs is greater than a 0.005" adjustment.

 

Then you get to the real issue for the vast majority of skiers - the mental and physical variation from day to day, pass to pass and buoy to buoy. Again IMHO, these variables have a significantly larger affect on performance than any small fin movement. Then you get to the conundrum that most skiers will "adapt" and revert to old/more comfortable habits over time that may negate the benefit of a fin movement. Think about when you ski at a new lake for the first time it can feel completly foreign. After a few sets, its normal. Sometimes "getting use to something different" is a real thing.

 

So.....for a beginning to intermediate course skier, you should set your ski to manufacturer's recommendations and leave it.

 

For more advanced skiers, you should focus on settings that allow you to ski more consistently. That is when you make a change, even if you can tell at the first buoy, ski it for at least a few sets before deciding if its better or worse.

[DW]

Any movement of the fin will 'change' the characteristics to some degree. I don't see the water ski fin adjusting community rounding the adjustments to the nearest half hundredth (.005") so when you finally clamp it tight and make record that measurement which will have moved slightly from where one intended it to be, that's whats recorded and rightly so. As noted numerous variables and 'white noise' in the system and out on the water have more impact than the smallest of fin changes, although depending on how sensitive the ski / skier is, .005" can probably be felt by a tuned in skier. Small movements can produce a significant change, water is 25x the density of air.

 

Until you know the effect of a change, one test technique to try, if you know directionally where you want to go, make a relatively large change which could overshoot the optimum, give you a good feel for direction then dial back to fine tune the change. That way ensures you should feel the first change and give you some confidence it actually made a difference. And always mark the original location so you can come back to it. A series of small moves can easily dial your ski right out of the performance window so proceed with appropriate caution.

 

As for a lab test, a water tank would be useful to collect data to spend the winter months pouring over and 'bench skiing' over the results:-) CFD would be another 'lab test' although the modelling is really complicated.

[RGilmore]

I had an engineering professor in college tell me that, if you have a 1" steel cable strung between two buildings under a 1,000 pounds-force tension, and a fly lands on the cable, it will bow (deflect). We may not have instruments precise enough to measure the bow, but it will be there.

 

Under that logic, a fin change of 0.001" will change how it skis... but it's doubtful you'll notice the difference. Therefore, I think anything within 2 or 3 thousandths of your target number will be good enough. And to put the whole discussion into perspective, legendary slalom skier Chuck Forrest, who has put up scores in -41', has been said to routinely set his fin "by eye".

[skibug]

@RGilmore one might argue that he was leaving something on the table by not adjusting precisely and may have run 41 with that added advantage.

[6balls]

Read "Fin Whispering"...great basics.

 

I was late to meaningful adjustments--grew up a hack who skied hard, then found some immediate success in the course. My adjustments were only as complex as the little card KD sent with the ski--it was like "want that thing to turn hard--move it forward and the front down---yeah and put the bindings forward while you're at it!" Measurements were basically the hash marks the factory put on the bindings. I tried to run skis forgiving of a lot of movement cuz I skied like a bull.

 

Once it was set up like a shovel (not suggesting that as advice), I always found I had a lot more to work on technically above the ski than below it. Slight changes in arm pressure, knee bend, chest open or closed--finding what works...was a lot more meaningful than fin and wing for me even as a guy who was running 35 off 36 mph on occasion.

 

After that when I got to 34 mph I got smart: I let @razorskier1 set up his skis with micro-tuning/coaching/consultation...then either stole his settings or his ski--worked great! All technique, baby!

 

Only once I was running 38 did I really start to understand and tweak on my own--because running it consistently presented a challenge where the margins really mattered.

 

So...long story, but agree with @horton set to stock and work technique until YOU are so consistent technically that you will not only feel but understand the adjustments by how it skis. Also agree with @Bruce_Butterfield re: boat/driver/wind/water/engine being large factors in how a skier feels/performs on their ski.

[jjackkrash]

"Set it to stock" is a bit question begging because it presumes you know how to measure it accurately and are measuring it the same way using the same reference points that the factory lists as "stock."

[liquid d]

totally agree with @Bruce_Butterfield for the majority of the time....once you are at the top of your game, looking for minute changes in the effect at shortest line, .002 or .oo3 will make a difference.

[JAS]

I suggest a blind test. It would be interesting to see who could identify a change, at what amount of movement, and in what direction. My prediction is that there would be surprisingly results that could change how we think of fin adjustments.

[A_B]

I believe when Jeff Rodgers set the World Record on his Goode, the stock setting for depth was 2.449, and before his round he was heard by Schnitz or someone talking about a scant "half or one or one" depth adjustment, so thinking it was 0.0005 or 0.001.

 

There are skis that you could almost throw the fin in backwards and run a pass and there are others that are very sensitive to minute fin adjustments or binding moves. The old Goode skis were 2.449, .690, 6.872 jaws with the correct Mitustoyo caliper, I don't recall the tips adjustment but it was north of 6.900. I found the 9100 and the 9500 pretty sensitive to very minor changes. Whenever I started skiing lousy, I would go back to reference stock and reset my skiing.

 

 

[kurtis500]

What about just switching out the fin material? Put in titanium or something and use the same shape...or narrow the thickness

[Horton]

@kurtis500

 

From 2008

 

Your current blade: HO and O'Brien have adjusted their blade thickness somewhat over the years. Goode, KD, Connelly and D3 appear to have settled in on relatively thick (Stiff) blades. As the Aluminum fin blade thickness varies the skier may feel that the ski is faster or slower and or more or less forgiving. Conventional Wisdom says that these perceived changes are because of the width of the leading edge. This is not completely untrue but the performance characteristics that are associated with thickness are actually more a function of flex. (With Aluminum as thickness increases the blade becomes stiffer.) It is true that the as frontal surface increases so does drag as well as lift but these factors are not the source for most perceived difference.

 

Flex Matters: An extremely stiff blade like those made from stainless steel or titanium will result in a very fast feeling ski that offers very good performance but only if the skier is in 100% perfect body position. By comparison a overly soft blade will most likely make the ski feel sluggish and cause the skier to be narrow. Another analogy is that a overly stiff blade feels like a very aggressive and fast Cruse Control setting and a overly soft blade feels like a slow boat time. The optimum blade for any skier is somewhere between these two extremes.

 

From 2003-ish

6 or 7 years ago one of the ski companies went from .095ish to .085ish and suddenly the skis felt more forgiving. The question that can not be 100% answered is if the ski felt better because of the softer flex or the change in thickness. I totally believe that flex is what made the difference. The downside is that these .085 aluminum fins sometimes break after a year or two of skiing. Since you can not change flex with out changing stiffness the answer can not be really solved. Breaking a fin is really funny as long as you are not the skier or you do not have to drive home with the skier who broke it. If are going to thin your blade be careful of fatigue. Otherwise please video all your sets. We all enjoy a good crash video. Joking aside all of the layups I worked with for CarbonFins were designed for a specific flex within a reasonable thickness. Prepreg carbon is about .006 thick per layer and .1 is about as thick as anyone thinks is a good idea so a fin can not have more then 17 layers. (.006 x 17 = .102) My 116 material is 17 layers thick and is designed to be softer then aluminum but not by much. The trick with the carbon is the order of the layers. If I could have gotten the stiffness of a 106 in to a fin that was .070 thick that should ski better. I do actually have some blem fins that are thin for the layup but they are not as stiff as the spec fin. It is a vicious circle. A component of stiffness with carbon as with aluminum is thickness. If there was money in it, there are a number of experiments I would like to try. Titanium has a lot of promise. I am thinking really thin but almost as stiff as aluminum. There are some more exotic fibers (high modulus carbons) then the sport grade I use that would offer more stiffness with less thickness. Since I am working with a plate that is less then .1 thick and we are talking about very slight differences in stiffness it is all trial and error. I have looked for real engineering help a number of times and all I get is quizzical looks. ¢Brien has at times run very thin fins without any breakage (better grade of aluminum?). At one time or another Wade and Andy have both told me that they think thickness is a big deal. I think the OBrien fins have at times been so thin because Andy thinks that a thicker fin creates lift. I have been told but forget what fin Wade runs on his HO. I am pretty sure that I recall being told that Wade does not run the current stock blade. (This info is at least a year old so he may be running the sock blade at this time - I do not want to spread false info). Badal runs my 106 that is roughly .095ish. FYI - it is not really a secret that I am slowly letting inventory run out and I am closing Carbon Fins. It is just not worth the effort. If you want fins get them while here are some left.

 

A number of ski companies have looked making CarbonFins but none have really followed though because it is just too much trouble for the price. I do hope that one of the big companies takes it on. I would like to see what I have done carried on.

 

My 2020 belief is that frontal surface was always a bigger deal than I realized. Leading and trailing surfaces create drag and we are hyper sensitive to small changes in drag.