Fin material thickness?

[skibug]

Does anyone have information about the performance of a ski based on the thickness of a fin? How do manufactures design the thickness of the fin stock?  Is it just based on standard aluminum plate that can be easily stamped out in mass production  I can buy a D3 blade (.093) for $12 a blade.  The older HO Xtreme tournament blades were (.083); but, new HO blades are (.093).  There has got to be some effect.

[RichardDoane]

It seems like the thinner blade would have less resistance, but more flex. This sounds like an answer that needs to come from the Coyote Brothers !

[Horton]

Read this 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.-----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.

There is more to the story but I have to get to work . . .

[Horton]

Did the above links cover it?

[skibug]

I get the idea. Obviously there are many factors involved.  I have machined down .093 fin to .082 just to see what happens.  If it works out; I am looking at doing some post hardening to give it some strength and then anodizing for protection.  I am just messing around with stuff to see how it reacts.  I assume that you guys went through a lot of this when starting with the Carbon Fins?

[Horton]

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.

[Deke]

What is the possibility of going "really" thin but using a steel alloy or spring steel?  Would you get the flex you're looking for and comparable weight if you went thin enough? Just thinking...

 Deke

[Horton]

No matter what you use, you are not going to be very stiff if you are very thin. Again I would like to try Ti

[skibug]

This will sound funny; but, I may have some scrap Ti plate at work.  I will have to check tomorrow.  If I don't, I know I have a supplier and all the free machining I want.  Maybe I will look into this.

[Horton]

we should talk. I have some carbon plate . . . .

[Horton]

I was looking for something or @skijay and found this in the archive. Seems like a lifetime ago now.

[Horton]

I love this link. If you will follow it you will see that Dr. Jim Michaels was on a CarbonFin. So funny.

 

https://web.archive.org/web/20031202141854/http://carbonfins.com:80/CarbonFins.htm

 

[BraceMaker]

So the verdict on thickness/flex of aluminum fins? It is interesting that the Whisper fin is offered in two thicknesses but that he is suggesting that you could order the thinner one regardless.

 

The difference between the two isn't that much in the grand scheme.

 

With fin fracturing - how many sets would a single fin have to see for that to occur- members of my family who have used one ski for 15+ years have no sign of that so is it a chemistry? failure of anodizing?

[UWSkier]

Aluminum failure depends on the number of stress cycles and the amplitude of the stress. Many non-ferrous alloys are subject to what's known as a fatigue limit, where even small amplitudes of stress will eventually cause failure. Steel doesn't have this issue. There's a limit to the amplitude that steel will withstand to infinity cycles.

 

 

Put another way, you can take your aluminum fin and flick it with your finger enough times that it will eventually fail. It might take you 400 years, but it'll happen eventually with near certainty.

 

 

 

[eleeski]

Has anyone ever had a fin break? Not just dropping out or going way out of adjustment but break. I've made some really weak soft fins but never had one break.

 

Performance drives fin thickness, not strength. And a fair amount of flex is optimal. So the thickness options we now have are proven performers. Get what fits in your fin box.

 

Eric

[HighAltitude]

Holy balls Horton! Didn't know your were into necro-posting. That's impressive!

(not saying it's not good stuff)

[Horton]

@HighAltitude me got history

[BraceMaker]

@UWSkier mere certainty but that logarithmic scale on the x means it will take awhile! How many ksi does a fin see?

[klindy]

Playing around with some steel grades might be fun. Well more than 90% of the steel grades used in auto manufacturing today did not exist 10 years ago. Similar but not nearly the same for aluminum. I mention this since the thread started 10 years ago.

 

Advanced High Strength steels (and Utrra High Strength Steels) have very specific engineering qualities. I’d be happy to do some investigative work if some metallurgically inclinded baller had some ideas.

[ALPJr]

@eleeski last year a buddy's fin broke approaching the first wake. Broke along the edge that @SkiJay described in another fin thread. Was a strage fall, more like he was shot out of a cannon and flew head first into the middle of the wakes. He was on his 20+- yr old Kidder - the same one that Sammy and Carl did the old magazine add with, riding on Harley's. Anyway cool thing was he called Wiley's and they had an original replacement fin. This year he finally broke down and got a Arc-S.

[Cam]

This fin broke on my HO Phantom at less than a year old found it in the lake a few years later, @Horton said there was a batch of them from that era that were breaking.

 

 

[eleeski]

Interesting failure. Looks more corrosion generated than overloaded. Note the stains indicating the fin was in the ski. Fin box issues?

 

Eric