Holes in your fin

[eleeski]

@Jody_Seal Great! Now I have another tuning variable.

One additional effect of a fin is resistance to rolling the ski edge to edge. But I want to roll quickly from edge to edge. Drill some holes on the end of the fin and the ski will roll easier. The fin will still track and stabilize. Holes in the fin are a win win.

I'm not sure I buy the lift theory for a fin. Or drag. The wing adds orders of magnitude more lift and drag. Those parameters are adjustable and relevant. Fin thickness, smoothness, holes, stiffness and maybe even shape are less noticeable than wings and their settings.

Eric

[thager]

I always thought shaping a wing like an aircraft wing would be a good idea. As an experiment a few years ago I took a regular HO wing that I had normally used and shaped it to resemble an aircraft wing cross section by rounding the front and trailing edges. No change was made to original foil shape. It was like throwing out a drag chute! Didn't make any difference what angle it was set to, the set up sucked the acceleration right out of my Elite! Put a normal HO wing back on and all was normal again. I assume this difference was induced drag caused by the negative lift of the foil shape. Experiment failed.

[wilecoyote]

thager, I think you hit the nail on the head, if you foil it, you make it so much more effective that it would need to be much smaller. What you did in essence is put a much bigger wing on the fin.

 

That's my thought with the main fin as well, I think we could make it much smaller if it was correctly designed. I think if it was done correctly the ski would accelerate better and hit higher top speeds, which of course would mean earlier to the ball with less effort. But where's the fun in that?

Chris

[thager]

I sharpened a fin leading edge once to cut down drag. Worked but not a good idea. It did leave a mark!!

[Chet]

A few years back a friend filled in all 5 fin holes for me. It slid like a trick. I reopened one hole at a time and with each new hole I received better traction and grip. With each new hole came some increased drag but worth the stability and holding power. Front holes seemed to be the most critical. Five holes or more were my personal favorite at the time. I had a few fins to play with but in the end I was convinced some smart ski teck somewhere in time had a clue.

[bogboy]

Ouch, my head is hurting. Horton, I think you should invest a bunch of money in this fin stuff. I think it could be pretty lucrative. Maybe I'll go in with you.

[tfriess]

Was just watching the worlds webcast..caught a glimpse of Nate's fin and it looked like there were about 10 holes in it.?

[Ryno]

So that's why Nate is so good! Nothing to do with technique, but rather he has a secret weapon...

 

I'm going to get the drill, 10 holes it is!

[SkiJay]

From my competitive soaring and winged formula car experience, I've learned that foil shape is hyper-critical. A truely efficient foil is only efficient within a very small envelope of speed and angle of attack before laminar flow gives way to turbulent drag.

 

While I think it would be a very interesting way to spend a pile of money and time, studying foil shapes for water skis may not yield much gain. The range of speed and angles of attack experienced by a fin are too extreme. You could optimize the fin for one tiny portion of the pass, but for the remaining ~98% of the pass, the foil would be so far out of its design envelope that it might as well be flat.

[wilecoyote]

@SkiJay I had considered that, but felt that if you optimised the foil for the pull section of the pass it would work well enough for the rest of pass, to end up with a considerable net gain over the current flat plate with holes.

 

Then last night I started running some basic calculations based on assumptions of what the angle of attack would be and it seemed impossible for the fin to be producing any lift at all. (in the traditional sense with laminar flow over the upper surface) Which of course we know isn't true so what gives?

 

I've been looking at the problem all wrong. I'm convinced now that the fin is operating in cavitation. That's why the flat plate fin works so well, it's actually better suited to operate in this region than a foil would be! The holes facilitate the cavitation. So through the turn, the speeds and angles of attack are in the region where a traditional foil would be better, but as we hook up and accelerate, the fin transitions into cavitation, and the holes actually encourage this. It's just a theory, but I'm pretty sure this is what's going on. This also explains Horton's observations that a thinner fin feels faster, the sharper the leading edge, the better the fin will cavitate. As a result the drag will be lower.

 

Chris

 

 

[SkiJay]

@Wilecoyote Regarding fin thickness:

 

Anytime there is more spray off of one side of the ski than the other, which is nearly always in the course, the ski is drifting sideways to some degree. The only time the fin is travelling straight through the water, is for an infinitesimally brief moment during the edge change. Since the rest of the time, the fin is being forced through the water somewhat sideways, I suspect the frontal area presented by the thickness of the fin has little to do with changing drag or speed.

 

The significantly increased flex of a thin fin, on the other hand, has a noticeable effect on a ski’s performance. As you load a thin fin, it flexes downward more than a standard fin, effectively making it bite and accelerate like a deeper fin. I believe it’s this increased flex that makes thinner fins feel faster; not their reduced frontal area which is a paltry 25 thousandths of one square inch over the rounded, sloped leading edge of the fin, and only for a fraction of a second during the edge change.

 

[Horton]

@SkiJay

 

You have stumbled onto the one thing one earth where I am pretty sure I know what I am talking about. I 100% agree with your first two sentences but over the years I have come to believe that the rest of your theory needs reconsideration.

 

Below is snip from the 2004 version of CarbonFins.com. This is what I believed at the time is also not 100% correct but pretty close.

 

The CarbonFins I made got slower as they got thinner because they got softer in flex.

 

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.

 

Thickness does impact speed because it equals leading edge and trailing edge size. The leading (and trialing) edge shape have a real impact.

[Horton]

I also played with fins that had the same thickness but different flexes and that was also dramatic. As with above stiffer is faster.

 

From the CarbonFins.com testimonial page

 

I love it!!

Dr. Jim Michaels

Men's 4 Record Holder / 1@ 9.75m (43 off)

[Horton]

Since I found all this old text .... This is what brought me back to skiing after 7 years off. Now I ski with an aluminum fin :-(

 

The Story:

In the Spring of 2002 we started manufacturing fins out of Carbon Composite for ourselves and found dramatic results. We found that the correct fin flex is far more critical to your skiing success then anyone thought. Just like with a ski, a fin that is too stiff is unforgiving. The aluminum fin that came with your ski is a good starting point but is too stiff for most ski/skier combinations.

 

The Coyote Brothers Research Carbon Composite blade has a softer flex and faster rebound then your stock aluminum blade. For most shortline skiers changing from a stock aluminum blade to a Carbon Composite blade will result in better consistency, smoother turns and a greater margin of error at the end of the turn. Skiers in the Jr. and Sr. divisions using softer blades skiing shortline at slower speeds experience much tighter turn radius.

 

The Theory & The Feeling:

The very end of the turn is where the highest percentage of the skiers inertia is pushing on the blade. This is also the point where a Carbon Composite Blade will flex substantially more and then rebound faster. The additional flex or "give" at the end of the turn with a Carbon Blade dampens the hookup just enough to give the skier a chance to improve body position and prepare to head for the wakes. This slight delay also allows the ski to finish with more angle. The "Feeling" is like you have a softer tail ski at the ball (without a loss of acceleration at the wakes).

 

Converts:

Converts to the Coyote Brothers Research Carbon Composite Blades include, 2006 Men III National Champion Greg Badal, eight time U.S. National Overall Champion Dr. Jack Horton, Slalom powerhouses Paul Crawford, Brad Hartwell, Mark Scheewind, Scott Gurnett, Brian Hockenbery, Will Bush and Bob Edie.

 

The Deal: All standard shape blades come with a 100% Money back guarantee.

[Horton]

@wilecoyote

lift is the generic term used in aerodynamics and by extension, hydrodynamics to describe the pressure differential

 

yea I should have known that - correction accepted.

[SkiJay]

Thanks @Horton. I've had this fin-flex conversation with some knowledgeable guys with mixed results, so your hard-earned firsthand experience is much appreciated here.

[bogboy]

Horton, sorry if I sounded inappropriate. I was just trying to be a little funny. My above post has been bothering me a little.

[Horton]

@bogboy yes it is funny. Don't Be silly

[wilecoyote]

@SkiJay, I agree with pretty much everything you said in the last post. But note, I'm not saying that the thinner leading edge has less drag simply because it's thinner, I'm saying that a thinner leading edge promotes cavitation, and thus brings the fin to a lower drag condition quicker. Same goes for the holes

 

Until I manage to get some proper numbers though, all this is just conjecture. We really need to know the angle of attack of the fin at all points through the pass, and as hard as I try to visualize it, I can't really make a decent guess. I'm envisioning me drilling some holes and making a special measuring thingy for this summer...

 

Cheers,

 

Chris

 

[tfriess]

http://www.perfski.com/Waterskis/Waterski-Accessories/Kepchia-ABS-Fin-Protector.html

[eleeski]

@wileycoyote and @SkiJay I don't buy the cavitation theory. Look at pictures of skis in clear water. The wake of the ski is fairly clean - inconsistent with a bunch of cavitation going on at the fin.

 

Trick skis have no fin (some of mine have no grooves either). Yet I am able to edge extremely well - often getting more angle at the wake than in slalom. I can throw a pretty good wall of spray and get a heavy rope load on my trick as well. My trick skis only slip when I want them to. I'm not sure how much actual work a fin must do to get a ski to turn - maybe none.

 

The fin on a slalom ski adds a huge amount of stability feel. But it is more like the feathers on an arrow than the wing of an airplane. Even the rudder (vertical fin) of an airplane does a completely different job (initiating and controlling turning) than a ski fin (stabilizing the ski).

 

Holes and fin flexibility may allow enough pressure relief through the fin to reduce cavitation!

 

Eric

 

@Horton the world needs your fins!

[Horton]

@eleeski makes me nervous every time I agree with you

[DW]

A few random thoughts on the topic and points brought up by the topic:

- what do the holes do: basically I feel they vent or bleed the pressure and change the pressure distribution across the surface of the fin -and- maybe more importantly, create some turbulence that reduces the boundary layer and allows the water to more effectively shed off the back edge thus reducing some drag and improving efficiency.

- a ski and fin operate in incompressible fluid (unless very close to the suface) so directly comparing to a wing in air is not always accurate. Incompressible flow has some very different characteristics (and about 25x the drag effect), so the aspect ratio and the thickness effects are quite different, hence the thin fin demonstrating a significant reduction in drag (it would not show that same effect in air compared to the surface drag and shape effects on drag levels)

- also, one needs to consider the transitional effect or rate of a ski going from one edge to the other, a very deep and short fin even with the same or less surface area will dratically slow that transition or really increase the effort required to make that transition in that time frame (think of twisting a short and long barbell back and forth as an example).

- the location of propulsion is significant, the bottom line is to make a ski "go faster" it's ability to hold an increased angle relative to the boat and rope and limit slip will define how fast it will go. The more it can hold angle and limit slip, the faster the ski will go since it will be forced by a solid rope and pylon to move downcourse at 34 or 36 mph, so more angle, more crosswise speed will result by simple vector summing. Added drag will only increase the force needed between the handle and bindings as that will be a twisting force rearward (core strength needed to overcome that).

- @Than: your experiment sounds a bit flawed if you rounded both leading and trailing edges. A rounded trailing edge will increase drag on a body, you also hit on a incompressible or supersonic flow issue by sharpening the leading edge, in air the opposite would result (look at a bullet as an example). Commercial jets have rounded noses, subersonic ones employ the pointed ones.

- The speed of the ski basically leaves it operating below the cavitation point (not so with a prop), but there are ways to introduce cavitation to the system. As noted, pictures do tell a good tale in this case.

[SkiJay]

At no time did I endorse the cavitation theory @eleeski. I also don't buy that a foil has application here. I do, however, think we may see a resurgence of different profiles and hole patterns in the near future. I also think @Horton may have been a bit ahead of his time with his carbon fins and that we'll see more of that again too.

[wilecoyote]

Cool, nice to see some quality analysis! I'm still leaning towards the cavitation theory though. We're dealing with a flat plate at a pretty high angle of attack here. (I think) From what I've read, (and I'm still reading because this 'hole' discussion has really got me thinking) is that even really well designed foils start to cavitate at around 50mph. A flat plate is hardly a well designed foil and I'm sure short line skiers are hitting well above 50 at the highest rope load part of the pass. I've been mulling over some simple methods to get some real numbers as to cross course speed and angle of attack, and when I get a chance I'll see what I can come up with. If anybody has some real data, I'd love to see it!

 

Either way, if we're not operating in cavitation, then a proper foil would be the answer to a much improved fin. If we are, then a symmetrical supercavitating foil would be the answer.

 

@Skijay, even the fins on an arrow (or rocket, or tail of an airplane) are creating lift in order to create the stability you're describing. That's how it works, as soon as the fin is not 100% in line with the flow (water or air) it creates lift that wants to push it back in line.

 

Chris

[Horton]

What @DW said

[eleeski]

@wileycoyote A barn door will generate lift. Arrows have thin feathers not airfoils. I'm sure Ghengis Kahn's DARPA tried foils at the ends of arrows but the thin fin is still best for an arrow.

Our ski fins are not normally loaded much. So they don't need to produce much lift. A cambered fun will have more surface area than a flat plate so at low angles of attack the flat fin should have less drag. Engineered surface roughness (golf dimples?) may be better at reducing drag.

Your foil idea may still work to improve buoy count. Throw that ski into a skid and it's slamming the brakes - maybe just what I need to crank that turn when I'm late. So many things I've tried have worked in a way I certainly did not predict. Please do the experiment - so I don't have to. My ankle is still recovering from my springtime fin experiments.

Eric

[BraceMaker]

@eleeski - neat bit - feathers used in fletching arrows have different sides, birds have left and right wings, and the feathers are different from the different sides, arrows when fletched with real feather vanes are airfoils, the feathers are usually mounted in some slight helical position, the feathers are all either rights or lefts depending on if the archer is right or left handed, and they generate different flights!

 

Not that I'm saying you need a foil wing. But knowledge is power!

[eleeski]

I may need a thick airfoil winged fin on my ski but whatever is on the back of my arrow will be thin..

Will Horton let you say "fletching" on this site?

Eric

[Horton]

@eleeski I had to look it up. Yes. Lucky for you ... I thought it meant something very depraved.

[wilecoyote]

Absolutely a barn door will generate lift. But it's L/D ratio sucks. I've been having a side conversation with the designer at Maui Ultra fins, (Dietrich Hanke, who has made significant change to windsurfing fins by applying the science from a pretty well informed background) his input and DW's has got me rethinking again. I think I had assumed way more load on the fin, and a higher angle of attack than it actually experiences. So we're back to an attached flow on the low pressure surface, which, then means if we pick a good foil section, we can reduce drag. How much is another question completely.

 

Chris

[BraceMaker]

@horton - any word has a different meaning when researched on certain city dwelling language resource websites.

 

In most cases however... there is a normal usage.

[eleeski]

@wilecoyote With so much excess power available in slalom, why is drag an issue? Wings on the fin, rounded edges, rocker, tunnels and a bunch of other features all add drag. And a low drag ski that runs on forever at the buoy feels awful to me. If holes add drag to the fin when sliding a turn, that's a good thing.

 

Additionally, the thin plate fin at zero AOA (angle of attack) will have less drag than a thick foil at zero AOA. More desired acceleration in the non turning (right behind the boat) portion of the pass.

 

However, as I write this I can think of many interesting things a foil shaped fin could do. Experimentation along these lines would be really cool - possibly revolutionary. Just don't fixate on reducing drag - try some shapes and see what feels good. Then use some physics to rationalize the magic.

 

Eric

 

@BraceMaker The Urban Dictionary has some warped hangups. Horton won't let us talk politics so we can't discuss Santorum no matter what. My arrows are straight regardless of the fletching.

[BraceMaker]

Who said UD? I do not recommend anyone purposefully pursue perversions nor memorize them for use in inappropriate professional situations.

 

Is obrien the only mfg to put a flap on the fin to have different fin surface depending on pressure differential? Are there any specific rules that govern wings/fins/ventrals?

[Horton]

@BraceMaker I did not say UD, I thought it. I had to look up some word that Eric used. For a second I thought he was using a word that means something .... I can't even think about.

 

Turns out he was using the right word for what ever he was talking about. So never mind.

[DanE]

You got me curious so I had to look this f- word up.

Now I wonder why @Horton felt the need to look it up in the first place!

[wilecoyote]

First of all, I've said it before, but I want to make sure everyone knows, as a slalom skier I'm really really new. I'll let you know when I finish a pass at -15.

 

So I'm coming at this with a windsurfing design background, and an outsiders view of slalom ski design.

 

I totally agree Eric. A very narrow planing surface, high angle of attack, copious rocker, concave, are all design aspects that kill the L/D. These design aspects are the necessary evils required to make a ski that can corner really aggressively.

 

What I suspect, is that a lower drag fin will allow the ski to accelerate out of the turn better, and while it's all well and good to say that the power is unlimited due to boat speed, the more overall drag on the ski, the further down course you go at the finish of your turn as the ski accelerates. The problem now becomes, when you get to the ball, you want a tight corner, and the slower you go the more feasible that becomes. Hmmm. What if you had a slightly higher angle of attack? It kills your cross course speed but makes the ski turn tighter. So we get a bit of cross course speed back by taking out some drag on the fin. I think that's why beginners like me should take the wing off, but the 36mpg guys need it. At slower speeds, the wing just makes it harder to get the ski up to speed, but at higher speeds, you'll never make the turn without slowing down.

 

The holy grail is a super slick ski going behind the boat that the will decelerate as soon as you start to lean into the turn. A lower drag fin would need to be accompanied by a new rocker line and binding placement. Not a simple thing methinks.

 

On the cavitation front, I've been scrutinizing all the video I can find, and it appears at first inspection that the fin begins to cavitate about 3/4 through the turn and lasts only a fraction of a second. If the only thing we get out of a foiled fin is eliminating that little bit of loss of lift, it might allow a slightly more agressive turn.

 

Sorry for the essay, but this stuff really grabs my brain.

 

Chris

 

 

[Horton]

@wilecoyote I totally agree Eric This is highly discouraged

 

the more overall drag on the ski, the further down course you go at the finish of your turn as the ski accelerates Not exactly. If less drag means less speed at exit then it is easier to be earlier. Some deep riding skis will back side the ball and carry a lot of angle - they are just require more physical effort.

 

What if you had a slightly higher angle of attack? I do not follow

[wilecoyote]

@Horton,

I thought that was a bit vague when I wrote it. A higher angle of attack of the planing surface has more lift, but also more drag (L/D continues to decrease above 5 degrees). Also,the higher your angle of attack, the tighter the turn. The problem therefore with a higher angle of attack is that the ski will be slower cross course. So what I was saying was that we might be able to keep the same overall drag by reducing drag on the fin and then capitalizing on the lower drag by getting the tip up a bit more so as to turn tighter.

 

What I meant by higher drag putting you further down course at the finish of your turn, was misstated. What I meant to say was that the higher drag ski (assuming all other things such as angle and exit speed are equal) would loose more ground down course than a lower drag counterpart. We're trying to convert as much of the force from the rope to speed as possible. So a more efficient (higher L/D) ski will do that.

[Horton]

Well this is a little frustrating. It sounds like you know what you mean but I have no idea. I understand what Angle of Attack is but like Eric said a ski fin is more like the tail fin on than a wing. Your fin is almost always sliding down coarse or outbound at a very high angle of attack.

 

The most pronounced impact of a fin is from edge change to apex. Most of this time the impact is more like the feathers on an arrow than anything else. I suspect that you do not need a fin at the wakes. Your ski has plenty of holding power when you are heading across but if you have ever seen anyone edge change without a fin it is a show.

 

Have you read this? http://www.ballofspray.com/home-v16/tech-articles-mainmenu/53-2004-lever-article (as the years go by see holes in this article but the basic premise still holds water)

 

[wilecoyote]

holds water he he that's a good one.

 

Our misunderstanding comes from which angle of attack we're discussing. When I'm talking about the planing surface, I'm talking about the ski. As the tip of the ski rises, the ski is able to turn tighter.(your lever analogy applies well here because the centre of lift moves aft as the angle of attack increases) Originally I thought that the fin was operating at a high angle of attack as well, but now I'm convinced that's not the case. As you and Eric have postulated, the fin is really only keeping the ski pointed in the right direction so it's angle of attack cross course is likely only a degree or so. In the turn however, we're putting a lot of pressure (you guys much more than me) on the fin. According to Rick (Maui Ultra Fins) a foiled fin is required for the slow speeds more than the high speeds. Apparently at the low angles of attack that the fin experiences cross course, a flat plate will perform nearly as well as a foil. It's the slow speed, high load part around the buoy where a foiled fin could earn it's keep.

 

I had read the "ski is a lever" article before, but only quickly. The tuning of fin and binding placement is consistent with windsurfing and surfing (no surprise there) but a few of the assumptions are a bit off (if I may be so bold) I think the ski as a lever concept is sound, but the conclusions as to why are not quite right. As the ski's attitude (angle of attack) flattens, believe it or not, the drag goes down. That is until you get below around 4 degrees, at which point it starts to go up again. Additionally, it's not the drag from more fin in the water that brings the tip down when you add more depth or move it aft, it's the increase in lift on the fin (pushing the tail deeper) and where that is on the lever. If we disregard the brief moment of edge change, the fin is always pushing the tail of the ski deeper, the less fin you have, or the further forward it is, the less it is able to overcome the skiier and the higher the tip will be. The problem is balancing a tight turn by a high angle of attack with too high an angle of attack and having the planing surface stall. Once that happens, we have to take too much rope load to accelerate. At this point we need to get weight over the front of the ski to get it to a more desirable angle of attack, but as we all know too well, you do that and the boat will just yank you into a face plant.

 

A high performance ski is a finicky beast, just move your weight a bit one way or the other and it'll make you pay. That's the reason why there's so much rocker in a ski. Rocker tends to stabilize the angle of attack. Assuming you had the skill to move your weight around correctly, flat ski would actually accelerate and corner better than a rockered one, but boy, you think your teeter totter is unstable now...

 

There is a misconception that a rockered board is "looser" in surfing and windsurfing because the board follows the curve of the rocker. The truth is, it's all about the angle of attack of the planing surface (see how I brought this all back to angle of attack? pretty cleaver eh?) The rocker stabilizes the planing surface and the board/ski rides at about the same angle of attack a bit less dependent on the rider's weight distribution.

 

Now, after all this discussion, extra curricular reading, and sleepless nights, I'm beginning to think a better fin design may have very little effect on our skiing. Go figure. Being the animal I am though, I'm going to have to experiment anyways. Too bad my skiing sucks so bad, I'll hardly be able to offer much of an informed opinion. I am, right now, however, heading out to the garage to remove the wing. I'll put it back on when I know I'm heading into the ball too fast. Probably never.

 

 

[DanE]

@wileycoyote " Additionally, it's not the drag from more fin in the water that brings the tip down when you add more depth or move it aft, it's the increase in lift on the fin (pushing the tail deeper) and where that is on the lever. If we disregard the brief moment of edge change, the fin is always pushing the tail of the ski deeper, the less fin you have, or the further forward it is, the less it is able to overcome the skiier and the higher the tip will be."ä

The above sentences seems a bit contradictory to me, wouldn't it be more logical that the fin is always lifting the tail when the ski is on edge (at least between the edge change and apex) and therefore you get a tip down attitude from the edge change all the way to apex with a larger fin far back and vice versa with a small fin moved forward?

Then it's quite a puzzle what happens after apex where there is some sideways skidding going on, I guess in that situation the fin could push the tail of the ski deeper.That would for sure exp

lain why a fin set too Deep Will add tip rise out of the onside turn.

[lpskier]

So who did invent/discover the holes in the fin?

[SkiJay]

@DanE Let me try to explain the more fin = tip lower phenomenon. When a hockey player or snow skier stops, there's a spray of ice crystals because the skates/skis are sliding sideways. The spray from a water ski is evidence that it too is sliding sideways while cutting and turning.

 

A deeper fin or one that is further back on the ski gives the back of the ski more traction in this sideways slide. The skier then has to engage more of the front of the ski to maintain the same cross-course angle or rate of turn. The more of the front of the ski the skier engages with the water, the less the front of the ski slides out. When the back of the ski is sliding out more than the front of the ski, the ski is rotating and carving a turn (rocker, flex, etc. also play here but I'm focusing on fin behavior). In fact, adjusting how the back of the ski slides sideways is what fin tuning is all about.

 

Without any skier input, the fin would make the ski straighten out. It's the skier who forces more tip into the water, and a deeper or more rearward fin forces the skier to engage more of the tip of the ski so it doesn't slide out as much as the tail. To the observer, the tip is seen to be riding lower.

 

There. That should make it about as clear as central Florida lake water.

[eleeski]

@wileycoyote Hmmm. I play with rocker on my ski a lot. The flatter rockered skis seem to work better for me - because they have a bigger sweet spot. Theory and ski feel often are not consistent. But I'm not going to nitpick you because I want you to experiment and report results - good or bad.

@SkiJay I'm not sure a agree with any of your explanation. Slalom spray is nothing like a hockey stop. Sideslides are a trick done on a flat ski not a normal part of slaloming. The fin does not steer the ski straight. Skidding is minimal. Tip pressure is a desirable skill - not a fin effect.

The ski edge is responsible for most of the skis performance. Angulate that ski onto an aggressive edge (a big angle) and it will perform for you.

For most of the time the fin just tracks. Deep, shallow it's not doing much so who cares. The fin does have a major effect on roll rate when rolling the ski from one edge to the other. Too much fin and the ski is hard to roll into a turn. Not enough fin and the tail won't stay in the water. Critical adjustment that can easily be felt - no wonder we play with fin settings.

Eric

[DanE]

@eleeski Agree that there is not much skidding going on from edge change to apex, but look at any overhead shots of slalom sking and you´ll see a lot of side slide from apex to hookup.

Therefore I believe a fin adjustment can have a positive effect in the first above said area but turn out to be negative in the second.

I.e a deep fin moved way back always make it feel to me that it´s easy to get tip engagement in the preturn all the way to apex, too deep and far back- not enough slide from apex to hookup to get a decent turn, always a compromise to get the optimum setting.

If tip pressure was a skill alone fin settings wouldn´t matter at all- what if you bought a ski delivered with the fin separate and you did not have access to factory settings or any kind of knowledge getting it close? Slap it on backwards and you´re good to go?

Also Schnitz claims if You go too short and deep with a fin (in his fin tuning tips he says you should aim for as short and deep fin as possible set as far back as possible within your abilities)

there is a risk of tail blowout through the edge change (never experienced that one though but I guess he has seen it all)

That points out there is a limit how much you can safely go to the extremes in fin settings.

[eleeski]

With non standard skis and fins, I set my fins as shallow as I can and not have the ski blowout in the turn. Radical fin settings only affect the turn for me. I have tried a backward fun - a little harder to turn and a little more apt to skip out in the turn - but I made passes.

The ski edge does the work, the fin just stabilizes things. Tune the fin to your stability taste.

Eric

[DW]

Skimming thru some of the latest thread info, it appears to me there is a bit of confusion on the axis and what component is actually contributing to the slip angle. Top down shot views showing downcourse slip when the skier is not vertical indicate the ski is the major slip component. In addition, overrotation and tail slip at this angle demonstrate ski tail slip, not fin slip. As Eric noted, try to "slip" the ski having the fin truly perpendicular to the water.

[SkiJay]

Wow @eleeski! You misunderstood me ... spectacularly. Obviously I wasn't suggesting a water ski's angle if attack was anything near that of a hockey skate during a stop, or that trick ski style sideslides "... are a normal part of slaloming." Please.

 

I intended this example to simply present spray as evidence that slalom skis do in fact slide sideways throughout most of a pass. If a ski tracked in the direction it is pointed as well as you suggest, there would be a lot less spray.

 

I totally agree with your statement that the ski's edge is responsible for most of the ski's performance, but to say that "most of the time the fin just tracks" understates how integral the fin is during all phases of the pass. Sure you can cut hard and turn on a trick ski. You can ski on a slalom ski with no fin in it too. Seth has been filmed running a 28mph pass on a 1x6 plank. But 32 off with any of these setups is going to be downright dangerous, if even possible.

 

I also agree with your statement that "The fin (has) a major effect on roll rate when rolling the ski from one edge to the other." I would add that whenever there is spray off of one side of the ski, which is all of the rest of the pass, the ski's path through the water has a significant component of sideways slide to it. And while ski shape does most of the heavy lifting, the fin is the tool used to trim that sideways sliding component so the skier can have as much control and confidence as possible.

 

Finally, I present these photos in response to your statement that "skidding is minimal." It appears from these photos that "skidding" is a significant component to a ski's path throughout the course. I'd also have to say that your assertion "Most of the time the fin just tracks" isn't supported by these photos either. The fin only tracks straight for a brief instant as the ski passes through the center of the edge change. The rest of the time, the fin is loaded and working.

 

Side-sliding during the cut:

http://dl.dropbox.com/u/1530989/Waterskiing/BOS/Side%20Sliding%20Skis/diabloshores2012_21.jpg

 

Side-sliding during the pre-turn:

http://dl.dropbox.com/u/1530989/Waterskiing/BOS/Side%20Sliding%20Skis/dos-drew.jpg

 

Side-sliding during the turn's finish:

http://dl.dropbox.com/u/1530989/Waterskiing/BOS/Side%20Sliding%20Skis/kc-wilson.jpg

 

The edge change is the only time the ski and fin are tracking straight as evidenced by no side-sliding induced spray:

[Horton]

@wilecoyote

 

You said: As the tip of the ski rises, the ski is able to turn tighter.

and

As the ski's attitude (angle of attack) flattens, believe it or not, the drag goes down.

 

I can see how you came to this ideas but it is the exactly opposite of reality – unless you are on a surf board.

 

The sign of a skilled slalom skier is a more constant and tip down ski attitude. Big fast turns ending with the tip up equal loss of water speed and are basically a stall. If you stall or wheelie, you then have to re-create your water speed from scratch. The boat does not wait for you.

 

If all your thinking is biased the idea that you want the less ski in the water at the apex - you need to start over.

The only times you may want less ski in the water are very brief and are to preserve speed off the second wake

 

You said –

Additionally, it's not the drag from more fin in the water that brings the tip down when you add more depth or move it aft, it's the increase in lift on the fin (pushing the tail deeper) and where that is on the lever.

 

This is a total mish-mash of my message. I never stated that more depth brings the tip of the ski down. In fact more depth brings the tip of the ski up at the apex. Length not depth brings the tip of the ski down 2/3s of the way from the wakes to the ball. Anyone who has added too much length knows the feeling of the ski sucking behind them just before reaching the ball line. The result is often a feeling like hitting a roller or a curb.

 

At the apex is when the fin slides the most. At this point fin depth is super critical. I call it grip (but I guess it is lift) Too much grip and the tail of the ski has too much leverage (resistance) so the tip comes up. Not enough depth and the tail of the ski is over powered by the skier and slides out.

 

I think the race car analogy is best here. Overstear vs understear. In the case of understear the tip of the ski bleeds pressure by rising out of the water. That energy has to go somewhere and the tail is not giving it up.

 

You said – flat ski would actually accelerate and corner better than a rockered one

 

Accelerate faster – yes.

Turn faster – no.