Someone Explain DFT to me

[jwr]

I thought I understood it, but evidently I don't. Fin forward makes for a shorter ski, that turns quicker with less tip in the water. Got a new ski and they recommend the bindings be set at 28.75. The farthest I could go back was 29.5. I've always heard that if you move your bindings forward you should move your fin forward so stock was .735, so I moved the fin forward to .755. Had a ton of tip in the water. So I moved it all the way to .800, and it was slightly better, but the ski was so aggressive, it was almost impossible to ski.

 

I was told to move it back to .715. The ski was millions times better, with less tip in the water. Makes we wonder if the sensation I was feeling was not too much tip in the water, but the ski just turning too quickly?

[klindy]

Where are you measuring to set your bindings. 3/4" difference is MASSIVE and can change a ski from turning like a bus to turning so aggressive you can't ski it. So lets sort that out first.

 

[jwr]

Yes it is massive, I'm surprised this ski is so good with my binders that far forward. I'm on Wileys, I measure from inside the horseshoe at the rubber.

[mwetskier]

the rule weve used is fin forward creates a sharper more aggressive on side turn fin back causes more tail slide in the off side turn. dont why this is true but it does seem to work that way.

[bishop8950]

Agree with @klindy, get the boots right first. Little point moving your fin a few thousandths of a time with bindings off by 3/4". It may require some customization to get your Wiley's where you want them

 

This said, your understanding of what the adjustments do matches mine.

[SkiJay]

To say "fin-back gets more off-side tail-slide" is misleading. It's more accurate to describe it as getting better off-side ski rotation.

 

When you move the fin back, you don't get more tail-slide. As you'd expect, the tail actually slides less. After all, you are giving it more leverage. But you also engage more of the ski's forebody which improves the grip at the front of the ski even more than the tiny improvement of grip at the tail causing the ski to rotate more. With more ski in the water, you also get lest overall drift so you carry a little more speed through this tighter turn too. Does a tighter faster turn sound too good to be true? The downside is that this tighter faster turn demands more accuracy so it's less forgiving.

[jwr]

I think there has been a bit of a misunderstanding. I'm not looking to make any changes to the set up of my ski. It's working great. I was just curious about the real effects of dft. It just seemed like the changes I made to dft were counterintuitive. Maybe a better question would be why do you change dft and what are the results? Does it raise or lower the tip of the ski?

 

[MrJones]

I get a bit confused about this as well. Skijay has a pretty good description of it (to my mind). Another way of describing it I heard recently was that moving the fin back gives the tail more "lift" or "support". This would be more of a "feel" than describing what it actually does to turning radius, etc.

 

(If Rossi or one of the other serious in the know guys wants to chime in here would be great.)

[A_B]

Moving the fin back "should" make the ski flatter on the water and slow the turns down. It also will make it run faster, so you should notice a longer glide when pulling out for the gate. I say should, because the variable is the skier, and the skier that rides my ski is not as predictable as fin movements.

[Steven_Haines]

I'm messing with the dft on my ski right now and what I'm feeling is that the further back (with in reason) the more it feels like it's on a rail(locked in). it also feel!s like it gives me better direction and more space before the ball. reducing the length and adding depth to keep your fin area in SYNC and allows the ski to turn hard. this is all based on my perceived feeling as I'm skiing.

[popof]

I'm not a huge fan of messing with ski setups for one good reason, I know that I know nothing about ski tuning :)

 

However, if I compare with other sports that i frequently practice (competitive tennis for my part), I have the habit of only changing ONE THING at the time.(grip or string tension or racket or balance or weight etc etc)

 

I'm pretty sure this advice's gotta be well known amongst the many fine slalom addict gentlemen on this precious website, I'm not saying I invented it :)

 

I'm sorry my advice isn't more helpful than what it is, but that's just my thought on this matter.

 

Good luck with your settings!

 

Romain

[ForrestGump]

@popof In the case of fin tuning, changing one thing at a time is in a lot of cases the incorrect move because one variable effects another variable. For instance, if you lengthen the fin(to get the tip to engage more on the offside)you might also need to take depth out or move it forward so you don't also hurt the onside.

[mwetskier]

@SkiJay - not an expert at fin tuning by any means so just offering the same words as this how to article

http://www.waterskimag.com/how-to/2010/05/24/how-to-set-your-fin-for-more-powerful-turns/

[SkiJay]

You've just highlighted why I decided to make such a thorough study of fin tuning for myself @mwetskier. The more research you do into the topic, the more contradictions you will discover. Respectable guys will list what they've learned through experience based on what they see and feel. More bite at the front of the ski makes the tail look and feel looser than before, so that gets described as tail-slide. But that description undermines proper understanding of the dynamics in play.

[jayski]

@SkiJay you need a job... ; )

[A_B]

@SkiJay, you got that right! Lots of conflicting info out there. Sometimes I wondered if dis-information was put out there on purpose. Then I thought nah, not in our sport.

[mwetskier]

@SkiJay -could it be theres more than one way to say the same thing? weve always thought of too much tail slide as causing the tail to slide completely out and schnitzes fin tuning guide says one fix for the off side tail sliding out is to move the fin forward. so if moving the fin forward reduces the amount of off side tail slide then it makes sense that moving the fin back you would increase the amount of offside tail slide. schnitz is the guy who invented the adjustable fin so we figured if anyone knows how it works it ought to be him?

[jwr]

So I guess I'm not the only one confused about dft.

[SkiJay]

@mwetskier Schnitz is d'man in these matters. But here again, the problem lies in communication. I'm agreeing with Schnitz and suggest that you may be misinterpreting what he's so correctly outlined in short expedient generalizations.

 

Two concurrent things cause the tail to blow out. The ski has a balance point near it's center. If you put too much of the front of the ski in the water, it acts like a teeter-tooter, and levers the tail out of the water. At the same time, the vastly larger surface area of the front of the ski bites so hard that the smaller tail of the ski slides more or skips out.

 

The blowout wasn't caused by a sliding tail, even though this is how it looks and feels; it was caused by too much tip in the water. Fin moved back puts more ski in the water. Fin too far back puts too much tip in the water and the tail may blow out. The cure - move the fin forward, not because fin forward makes the tail slide less, but because when less ski tip is in the water, the tail is riding deeper at the other end of the teeter-totter, and it's not being overwhelmed by superior grip at the front of the ski.

 

@jwr You are most DEFINITELY not the only one confused by DFT, and we haven't even started with how DFT affects the on-side, the cut, the edge change or the pre-turn.

[mwetskier]

not trying to argue, but at this point i am seriously confused. if moving the fin back too far can cause too much tip in the off side turn and that can cause the tip to dig in more and because of that the 'tail of the ski slides more or skips out' doesn't that mean the same as saying moving the fin back can cause more off side tail slide? is its just 'semantics' that make this so confusing?

[SkiJay]

@mwetskier You are absolutely right. It is semantics. If it looks like "tail-slide" and feels like "tail-slide" then it must be "tail-slide." It's just that tail-slide is a symptom, whereas too much ski tip in the water is the actual root of the problem. And speaking in symptoms can easily lead to confusion when it comes time for custom fin tuning. For example, if you believe that a move back with the fin made the tail of the ski looser, you may add more depth or move your bindings forward to fix it, which would make the actual problem of too much tip-bite even worse. Fin dynamics is the classic case of a little bit of knowledge can be a bad thing.

[mwetskier]

so thinking of trying the mapple 6.1 which is supposed to be wider in the front of the binding. do you think this width in front is likely to make the dft move were talking about more pronounced or less? either way will different ski designs make various fin changes work differently than expected with 'standard' ski designs?

[rawly]

If you are gonna try the 6.1 , just e-mail Andy with your questions. He is serious about the customer relations part of his ski company. He will get back to you. As busy as his life must be,he will have time for you.

[SkiJay]

@mwetskier Different ski designs will not make the various fin changes work differently than expected with 'standard' ski designs. The proportionate effect will vary from design to design, but the effect of each fin change will be as expected.

 

Keep in mind that there are limits to how far you can go with each change before you start to create imbalances that yield unexpected and possibly undesirable results. But if you don't stray too far from factory specs, I'm pretty confident that fin changes will affect ski behaviour as expected, albeit disproportionately, with any current ski design.