Fin Length

[schroed]

It seems that most people believe that adding fin length will drive the tip of the ski in the water. Some ski manufacturers further claim that this is more noticeable on your offside turn. I'm wondering why this happens. Is it due to an increase in drag that creates a rotational moment which rotates the tip of the ski into the water or are there some other forces at work here? If it is simply drag, why is the tip pressure more prevalent on your off side turn as some ski manufacturers suggest?

[mwetskier]

ur weight naturaly shift forward in ur offside because you turn ur offside with ur front foot so the xtra drag multiplys that. onside you turn with ur back foot so ur weight is already going back wards but a longer fin does make ur onside little harder to turn its a trade off

[Horton]

http://ballofspray.com/home-v16/tech-articles-mainmenu/53-2004-lever-article

 

My theory

[schroed]

@horton : Thanks. That's a good article and the kind of info I was looking for.

[Horton]

@schroed

 

That article is almost 10 years old but from a 40,000 foot level I think it still holds mostly true.

[SkiJay]

@schroed You are right in saying "It seems that most people believe that adding fin length will drive the tip of the ski in the water." It's a statement that makes me nuts because it promotes misunderstanding.

 

The fin doesn't drive the ski tip into the water, the skier does. The longer the fin, the easier it is for the skier to engage more tip. Think of it like adjustable power steering in a car. If you increase the boost in power steering, turning the car will get easier and easier, but at the expense of feel. Too much power assist/fin length and the handling gets vague, numb and even unpredictable. Less power assist/fin length and the handling is heavier, but consistent and predictable.

[Horton]

@SkiJay I partly disagree. Too much tip will make the ski stick as you come off your edge change. It is literally drag. You need some - the pros tend to take the least.

[h2odawg79]

@Horton

 

Can you reiterate:

 

#1. " Too much tip will make the ski stick as you come off your edge change"... Please define/describe the term "Stick" as it effects the skier from edge change through the pre-turn.

 

#2. If it is caused by "drag", then would this be the drag of Total Fin Surface area? Where as even too much Depth would alter the edge change in the same manner?

 

Thx

 

[The_MS]

Too much length will cause lean lock. Its just hard to roll the ski off its edge.

[wilecoyote]

http://www.ballofspray.com/forum#/discussion/6946/holes-in-your-fin/p1

 

Bottom line, it's not the drag, it's the lift and the drag. The fin is providing resistance to the tail sliding out and that pushes the tip down. Moving the fin back or making it bigger (adding depth) will both bring the tip down.

[Horton]

http://media.tumblr.com/fe497dd337d9af8479bb6398b9565d16/tumblr_inline_mg6n5ltl6X1rxe4lt.gif

[Horton]

@h2odawg79

As you add length the drag increases and as the drag increases the ski is pulled back under your mass – the ski is pulled /forced deeper in the water. There is a critical point where there is suddenly too much ski in the water and it feels like you have hit a roller. The ski abruptly slows down.

 

You can change the amount of ski in the water and the attitude with the other two directions of adjustment but you will feel the effects of length most dramatically in this way.

 

Your point # 2 - yea I guess so. I do not approach fin set up in this way.

 

[skibug]

I'm with @Horton.....

[h2odawg79]

@Horton o.k., #1. "Stick" is refering to the attitude of the Ski after changing edges. i.e. Too much leading edge creates a ski that feels "Stuck" and is not as "Free" in the Pre-Turn, possibly resulting in reduced Out-bound direction and/or a reduced ability to physically direct the Ski.

 

#2. "Drag" is the direct result of Ski surface area in contact with the water from its altered Attitude. -not drag created by the increased surface area of the Fin itself.

 

Cool, Thx

[Horton]

Yes No Maybe Sort of

[h2odawg79]

I know zactly what yer trying to say

[SkiJay]

It's good to know that if you have too much fin length (for your technique), the ski will "stick" as you come off your edge change, but it's better to understand "why" this happens.

 

The more length you run, the easier it is to engage the front of the ski. If you are not used to the tip engaging real easily, your normal skiing inputs jam too much tip into the water and the ski turns too hard too early, essentially jamming on the brakes (I like Horton's analogy that it feels like hitting a roller). Out of the edge change, this makes you narrow. At the ball, especially the off-side/toe-side ball, it can break you at the waste. Worst of all, it screws with your confidence and technique.

 

A lot of amateurs who tweak, end up with too much fin length. All it takes is to get a little defensive on the ski and the resulting tail-riding stops the ski from turning well. Auto-response: the fin needs more length to get the ski turning easier. Sure it turns easier, but now you have an unpredictable ski. It's now so easy to over-engage the tip, that sometimes it bites, so you get a little daintier on the ski; then it wont turn. What's most confusing is that sometimes you get it just right, lulling you into believing the setup is good. But it's not. It's too vague and unpredictable.

 

With less fin length, it takes more effort to over-engage the tip, so tip-bite happens less often. You get to ski more aggressively and even less refined and will be far less likely to over-engage the tip.

 

Moral: err on the side of running your fin length too short. The ski will be more predictable, have more feel, carry more speed, and build width easier.

[h2odawg79]

Great explanation Skijay.

 

I use Radar RS-1's and also have the Strada bindings. I feel that they are a bit finicky (light) on Tip pres. (the RS-1's are a much better set up IMHO) I've had two different Radar Ski's that for me, both required a bit More Leading Edge (Length) just to get them to turn on my Off-Side. (can't bring myself to say "Toe-side on a Slalom ski!)

 

With Stock settings, I had a very, Very nice (too good) On-Side with both ski's, but the Off-Side would not engage around the buoy. Adding more Length made the Off-Side Much better and "might" have taken away a tad on my On-Side. Too much Length and I will have trouble with Speed and Width. (NOT a good thing!)

 

But as you mentioned, the "Optimum" set up is very elusive b/c everything is a Trade Off! I have been logging my set ups and factoring the Total Fin Area to try to better understand the set ups and the end results. -especially when the water temps swing 35+ Deg's seasonally.

 

Kinda hoping AM will take pity on me and lay me a Golden Egg (6.0) next Season!

[Ed_Johnson]

Skijay brings up a good point...Instead of Factory Settings, I have found what I call "Personal Settings." On my last 4 skis, Goode Mid, Nano, Sans SR2, and HO S-2, I always started with Factory Settings and after tweaking for some time, always ended up in the same range, what I call my "Personal Settings." These for me work out to be 6.750 Jaws or 6.820 Tips, 2.50, and .750 DFT. Wing is variable for water temp.

 

If and when my 68" A3 I ordered 3 months a go ever gets here, I will this time START with my personal settings and forgo the Factory ones. I am sure this will save a lot of time and effort.

[Horton]

Scot Jones did that for years. He always used a old Goode setting for every ski. I think he has changed his mind about that in the lase few years.

[Wish]

I gotta think with the new and different shapes, bevels, materials that factory settings would be the place to start. But what do I know. Took forever to set up that S2. Still not convinst I can't make it better......Hi my name is Wish and I am a fin tweeker...it's been 3 months since my last tweek..

[SkiJay]

Here some interesting fin-length related footage. Last week I was experimenting with extra fin length and in addition to the vague unpredictable tip engagements outlined above, I thought I noticed the ski porpoising during my offside lean. I cranked a nice hard off-side lean and captured the results in this video. The on-side was fine, but the offside quickly developed an uncontrollable hop every pass despite nice calm conditions or anything I could do with my body position. In the second half of the clip, I took out only .007" of fin length, and the ski dropped into a nice hard stable lean. .007"! Things that make you go hmmmmm…

 

[h2odawg79]

@Wish, @Horton has a 12 step program for that! -I think there is a Big Rum party or something at the end of the program. I never made it that far. -My Mother in Law always said I was nothin' but a Low Life tweaker...

 

@Skijay, Very Cool clip! Yes, .007" is certainly note worthy. -that's about the same thickness as 4 Human hairs! Right Horton?

 

 

[SkiJay]

@h2odawg79 The average human hair =.003" so .007" = two Italian hairs =)

[wilecoyote]

Wow, I must have watched that clip 100 times! It really drives home your point about being able to engage the ski more. My initial reaction to your post before I saw the video was that more fin should have meant a more stable ski not less. Porpoising, is caused by too high a trim, so one would think more fin would calm that down. But, as you pointed out above I think you were able to drive the tip down too much, and it bounced. That's a serious discovery for all of us! Something else really interesting that I noticed was where you were pulling from on both clips. On the first pass, the centre of pull moves back much earlier than it does on the second pass. On the stable pass the rope stays in front of your foot until you've solidly established your lean and then it moves back as you gain more angle. On the unstable pass, the rope is already there from the beginning and you never get the angle. Very interesting indeed. Thanks for posting that.

[ForrestGump]

I want to throw a monkey wrench in the discussion after seeing someone post that most pros run less length. I've found more than a few pros running a really long, deep fin. One of the reasons I was given was that the ski is more stable in rolly water and chop. I've actually seen a pro pull a new ski out of the box, loosen the fin clamp, make the fin as deep as it would go, as long as it would go, and push it all the way back, then tightened it back up. I said "You're not going to measure that?" He then went and ran 39 off, came back and asked "Still think it needs to be measured?" So I got my caliper and it was 7.11 long, 2.550 deep, and .580 dft. Can you say boat rudder. haha

[h2odawg79]

39 on a Speed Ski? Man, imagine what he could do on a Ski set up within a Hair or two!

[jackski]

BTW Horton the Panda is Great