Why do fins have holes?

[Horton]

I was asked this yesterday & gave the same answer I was given 20 years ago. That answer is that the holes are pressure relief from the high to low pressure sides of the fin. Is there a better answer?

 

@AdamCord‌

[bowty]

@Horton‌ wing mounting maybe?

[Horton]

@bowty‌ I am pretty sure there is more to it than that.

[Than_Bogan]

Always assumed it was for making Holy Water.

[Lovell]

I don't know, but one of my old kidder's I had as a teenager (1988) had a fin with no holes and a wing. The fin had a triangular shape, every ski before or after has had holes in the fin.

 

I used that ski through 22 off and never had any performance issues.

[Taperflex]

The original story I got was that back in the '60s, the winner at the Masters had a hole in his fin. Everyone was sure this was some secret weapon he had discovered, so everybody started drilling holes in their fins. When someone finally asked him about it, he said it was so he could hang his ski up on a nail in the boathouse. True or not, it makes a great story.

[lpskier]

I remember when holes first appeared in the early 70s. Skis were still made of wood and fins were still screw on rather than drop through. If two holes were good, ten were better. Some fins looked like Swiss cheese. Most holes were between 1/4 and 3/8ths of an inch.

 

An equally interesting question is "What is the origin of the holes in the fin?" The story that I heard at the time was that Bab Mahar from Maharajah skis received a shipment of fins at his shop. He looked around for a place to store them, but found none. So he drilled a hole in each fin so he could hang them on a nail on the wall. He then discovered that the skis with the holes worked better than the skis without the holes. True or false?

 

WIngs came way after holes in the fin.

[dchristman]

A blurry picture from a 1977 book claiming the holes are for pressure relief:

 

 

Interesting that Joel McClintock doesn't even mention fins in his book from 1980.

 

Like @Lovell‌ I also used a Connelly "Tournament" fin with wing and no holes in the early 80's. It was an aftermarket item - the ski came standard with a fin with holes. Did it make a difference? It's too long ago for me to remember if I even compared them.

[mwetskier]

steve schnitz has studied a lot about this in terms of what the holes do and how number and size of holes affect the turn. most interesting to me is he says that altering individual holes can change different aspects of the turn depending on where those holes are on the fin.

[lpskier]

@Taperflex Ha! The Swiss cheese skis I am referring to were Taperflexes.

[ozski]

There is some talk that adjustable holes are on the way.

[mwetskier]

@qzski -thats a misnomer. the holes them selves will not be adjustable the fin itself will be adjustable around the holes.

[thager]

Sphincter Fins?

[eleeski]

Why not?

 

Start with a blank fin, add holes for as long as the performance improves. Forget about the why, just ski with the most comfortable fin.

 

Analyze fin holes during the winter on the internet far from real skiing. Should I put holes in the bases of my snow skis?

 

Eric

[Dirt]

I added an extra hole in the back of my A2 fin. It let the ski come/slide around better but did not track across the wakes/hold angle as well. It definitely makes a difference.

[bassfooter]

@eleeski‌ - Some downhill skis have a hole in the tip. For climbing skins? Anyway, with as little snow as Mammoth and Tahoe have right now, you can put holes in your bases just by skiing on them.

[eleeski]

@bassfooter‌ Yeah, my skis are in getting tuned tonight from the rock damage and need for edges on the Tahoe boilerplate that is everywhere at Squaw. Nothing worth hiking for yet. Pray for snow.

 

Fins are important for ski performance. Holes are just one aspect of fins. Flex matters too. And fin placement - but .001 isn't ever relevant.

 

Eric

[Horton]

Chet can't long in - my fault not his. He emailed me the below post

 

Hey John

On your site people were wondering about holes in fins.

A few years ago a friend of mine did me a favor and used some sort of metal bondo to fill in the holes on my 3 of my favorite fins (all identical).

I was excited to ride the ski without the holes to draw my own conclusions.

First set ...first pass I almost did a trick ski like side slide.

As you would suspect I began to knock out one hole at a time.

Each time the ski slid less and tracked out of the buoy better.

As I remember the rear fin holes were the most critical to performance.

Cool experiment but for now I like holes.

Too many can really slow a ski down in contrast (increased drag).

But slip or tail slide diminishes with increased holes.

Hope this helps.

Chet

 

[Than_Bogan]

I am FAR FAR from an expert on fluid dynamics, but Chet's experience seems to confirm something that I was thinking: I don't think there is a lot of water passing through those holes. If it were about that, then we'd expect adding holes to cause more side-slide, whereas Chet found the exact opposite.

 

I suspect the holes have a lot more to do with disrupting the laminar flow in some way that ends up being beneficial. To state it VERY imprecisely, they may give you some "grip" on the water.

 

Iirc, Gator1's "crazy" fin grooves were directed toward disrupting laminar flow in a particular way, and I wouldn't be surprised if ultimately some carefully placed grooves are "better" than holes. (Nor would I be surprised if we actually want all of the above.)

 

As usual: Theory is required to narrow down what is worth trying (since we have infinite possibilities but not infinite time). But only trying it can tell you if it works.

[DW]

Pressure relief as JTH noted and they generate some beneficial turbulence as Chet noted. Somewhat similar to vortex generators on a wing or surface and like feathers on a bird wing. The holes also allow the fin to move the leverage center deeper as an example to improve the tail blow out without the detrimental effects of a too deep fin depth.

[estrom]

Back in the early-mid '80's, my buddy had Connelly's top ski, the HP, (which is what Mike Kjellander used at the time) that had no holes. It also had an odd shape to it.

 

[6balls]

@DW is on it if a foil through water shares properties with a foil through air (aircraft wing).

 

In the air a turbulent boundary layer over the wing is less likely to separate from the wing than a laminar boundary layer. Thus adding vortex generators keeps turbulent flow over the wing, and hence control, in situations where it would separate otherwise...such as high angles of attack to the relative wind. Separation creates loss of airfoil control followed by aerodynamic stall (loss of lift).

 

Would make sense that filling fin holes as Chet did would create a more laminar flow which is more likely to separate at high angles of attack causing loss of control and hydrodynamic stall.

 

Could be full of baloney I'm no expert...just happen to have vortex generators on the Mooney and I know how they work and also the before/after story in flying it both ways.

[Wish]

I have an 80s HO Mach 1 - no holes.

[dchristman]

80's Connelly Tournament Fin. The holes are for the wing.

 

[Horton]

@dchristman dude you have some classics

[Horton]

@AdamCord‌ you know you owe me. Come on ... you want to comment.

[lakeo]

Than- a fin with grooves. now that might be interesting. John?

 

[dchristman]

Sigh... if only my wife appreciated my classic equipment, @horton

[Horton]

@lakeo again the old school explanation is that he holes allow some pressure equalization from the high pressure side to the low pressure side. Just like the low pressure side of and airplane wing sucks a plane up (all the smart guys just barfed on their PCs) the low pressure side of a fin has more impact than the high pressure side. So turning 1/3/5 the low pressure on the left side of the blade is what keeps the ski from swapping ends more than the right side which is pushing all the water.

 

The holes bleed water to the pressure side.... hell I don't know.

 

When I was making CarbonFins I tried a number of things that would have an effect similar to grooves and did not see any impact.

 

Again this is the explanation I was give 25 years ago. @AdamCord‌ be nice when you tell me how incredibly wrong I am.

[TylerR]

http://m.dummies.com/how-to/content/the-different-types-of-fluid-flow.html For those of you who would like a basic explanation of this concept.

[MattP]

Right now the industry has two different common patterns one is a 4 hole and one is a 5 hole. The 4 hole is used by Mapple skis and still at O'Brien?(it was). Where the five hole is being used by majority of the other manufacturers. When testing skis do the companies test multiple fin hole variations or do they stick to what they know and have used in the past.

@Horton‌ you designed fins at one point in your life. Did you do any hole pattern testing?

@AdamCord‌ thoughts. Insight?

[thager]

@dchristman‌ Relax, you've just been married too long! Maybe time to get a new stick?

[lpskier]

I'm developing a fin that only have holes on one side.

[AdamCord]

Of course there's never a straight forward answer with anything in our sport, especially when it comes to fins. The fin sees water flow at multiple directions, pressures, speeds, etc, so something as drastic as drilling holes in your fin is going to have multiple different effects. That being said, there is one major thing that the holes in the fin do, and I am pretty sure that reason is why they were originally tried, and why they are still used today.

 

Holes in the fin make the tail sit deeper, cause drag, create stability, and reduce the chance of a tail blowout in the turn. This is why all skis have them, and I think this is why they were first tried. If we spend some time thinking about the dynamics of the water flow on the fin, we can see why holes makes perfect sense.

 

First you need to imagine the ski at the finish of a hard turn. The ski is banked up very far, it's sliding a lot, and there is a LOT of pressure on the fin. If we consider a 1 ball turn, we know that the right side of the fin will have high pressure on it, and the ski might be banked up ~45 degrees to the left. That also means that the fin is angled at 45 degrees compared to vertical. Now let's think about what that means as far as water flow. This flat plate (fin) is pushing through the water very fast at a 45 degree angle pointed toward the bottom of the lake. What will this do to the water flow? It's going to try and push a lot of water up, and drive itself deeper into the water. That's great, except that there is a ski attached to that fin. The water that is being driven up by the fin is slamming directly into the bottom of the ski.

 

All that water flowing up from the fin and hitting the bottom of the ski creates a very high pressure area at the fin/ski intersection, and it creates lift, which will make the tail ride higher in the water. Lift is great if you want a really fast ski, but not so much if you're looking for stability. By putting holes in the fin, we've created a path for some of that high pressure water to escape. So there's still pressure there, and there's still lift, but the holes reduce it quite a lot.

 

Ok so let's think about the example the great Chet Raley gave above for when he tested a fin with no holes, and see if that makes sense. He said:

"First set ...first pass I almost did a trick ski like side slide."

Ok we know that the tail is riding much higher in the water, which will reduce grip and stability, making the ski slide a lot more....yup.

 

"As you would suspect I began to knock out one hole at a time.

Each time the ski slid less and tracked out of the buoy better."

Each time the pressure lifting the tail reduced, and caused the ski to pull deeper in the water. This is exactly what creates stability/tracking and makes the ski slide less.

 

"As I remember the rear fin holes were the most critical to performance."

So this is interesting, and it makes perfect sense. As you can imagine because the ski is sliding, but is also moving forward, the pressure builds on the fin from front to back, and is highest at the back. We also know there is more surface area at the back of the fin, which compounds this further. So the holes in the back of the fin will have the biggest effect on tail lift.

 

Of course nothing is without compromise. The holes will make the ski slower by causing drag that we don't want in other parts of the course. Also the holes have some other effects like making the ski easier to roll up on edge, reducing the fin area, and of course giving you an easy way to hang your ski from a nail. But this example above is the biggest reason for holes.

 

@MattP is there room for improvement? Absolutely. But fin testing is hard and the shapes we have today have been molded over many years of testing, and we know they work. That's why it's not surprising that manufacturers don't seem to change fin shapes very often. Besides, you're not going to buy a new $2000 ski just for the fin are you? ;)

 

 

[Horton]

@AdamCord‌ so in your way of thinking my explanation is completely whack?

[AdamCord]

I'm not sure I follow your explanation...something about an airplane? Yes water flows from the high pressure side to the low pressure side, allowing for pressure relief.

 

@lpskier Obrien did the fin with holes on one side years ago with a vent flap. Pretty cool idea actually.

[Horton]

@AdamCord‌ it is a suck vs blow thing I guess

[Than_Bogan]

@AdamCord. Firstly, thanks for taking the time to write that up and inform us!

 

I'm not 100% sure I understand yet, but on the off chance that I do:

 

It seems to me that holes in the fin are kind of a compromise solution to the problem you discuss: they help reduce the (bad) pressure on the bottom of the ski, but they also reduce the (good?) pressure on the fin itself.

 

So wouldn't we be better off to relieve only the component we don't like and put the holes (or slots or whatever) in the tail of the ski!?

 

As a "bonus," I'd expect this to throw water up in a hilarious looking rooster tail during the hardest parts of the turn.

 

Did I just revolutionize ski design? :) (That part is tongue-in-cheek, but my suggestion is serious. Does it makes any sense?)

[Horton]

Than_Bogan you may have just made @AdamCord‌ spit coffee all over his keyboard

[bigtex2011]

where is the panda and chuck norris

[AdamCord]

@Than_Bogan there will be no coffee spewing this morning. Holes in the ski are a great idea! This is what the ski I rode for most of the summer looked like:

 

@adamhcaldwell and I came up with this idea this summer and tested it with a surprising amount of success. If any manufacturers are reading this and want to use this idea you can send the royalty checks to me, not Caldwell. ;)

[Horton]

@AdamCord‌ you're giving away all the best secrets

[AdamCord]

@Horton I'm definitely not giving away the best secrets. I worked too hard to discover them. This is cool, and it works, but it's not on the "best secrets" list.

[Horton]

@AdamCord‌ I agree that you need to keep the biaxially oriented flow disruption sphincter fin a secret

[AdamCord]

How dare you mention the BOFDSF!

[liquid d]

No patents on that ski design with holes?

[disland]

holes in the wing would be interesting to try. I am sure someone has tried it

[Horton]

@disland‌ I have seen it done

[gt2003]

@AdamCord , does the ski have a standard hole pattern on the fin as well? Interesting that no matter how far things advance, new ideas are pretty much always out there.

[AdamCord]

@gt2003 we tested the holes with a variety of different fins. Divulging the results of that testing is a bit further than I want to go in a public forum, but let's just say we had some really exciting results.

 

*Begin Rant >:)

I agree there are always ways to push the boundaries further. In slalom skiing I feel like we've barely begun though. Grab a ski off the shelf from 20 years ago and put it next to the top skis today. Other than weight and graphics, there really isn't going to be a huge difference, and the average person won't be able to tell them apart. That tells me that either skis were really advanced 20 years ago so there isn't much improvement to be made, or more likely, skis just haven't advanced very far in that time. Take one of the top skis from 20 years ago and rebuild it with new materials, and I guarantee it won't feel that different from today's skis. The main problem is that it really takes a lot of effort and critical thinking to achieve a meaningful breakthrough in ski design. Ski companies don't have teams of engineer skiers out building tons of prototypes, testing one variable while controlling for others, meticulously documenting everything, failing, trying again, etc. over and over again. But that's what it takes, and for what skis cost, that's what they should be doing.

*End Rant >:)