Check your fin

[Cam]

This was found in our lake last year, it came off my HO Phantom when it was only one year old.

 

It was one of the scariest things that has happened to me on a ski, I remember coming out of 3 ball OK but feeling totally out of control by the time I reached the wakes.

[klindy]

Did you purposely cut off the top section where it clamps into the fin block? If so, there's enough material missing that there couldn't have been a lot holding it onto the ski. If you didn't cut it off my question is did it break off when you lost the fin?

[Cam]

It was an untouched stock fin that snapped off the rest of it was left in the fin block.

[MattP]

@Cam do you ski in salt water?

[Cam]

@MattP I spent a week skiing in salt water with that fin before it broke, but I washed it down with fresh water after each set and stripped down the fin block and cleaned and greased it at the end of the holiday.

[dtm]

I had a fin break on a Phantom too. Happened right at the wakes coming from an on-side turn. One of the nastiest crashes I've ever taken. The reason the two tabs are still there is because the fin box did not properly clamp down on those two tabs, leaving it prone to premature wear. The fin box was one piece, connected at the front and the back. These connections inhibited the three screws from being able to tighten the fin box along the entire length. I ended up cutting the fin box in two with a band saw. If you ski on an HO with one of these early fin boxes, I would check to make sure the entire fin is getting secured.

[Chef23]

That happened to a friend of ours a couple of years ago on a Phantom. Fin sheared off and led to a nasty crash where fortunately the guy didn't get hurt. The ski had never been in salt water.

[Horton]

That happened a lot about 10 years ago. There was a batch of HO fins that skied really good but that broke. Unless you are on a 10 year old HO I would not worry about it.

[A_B]

Bit me too. Of course it happened when I was heading into the wakes. Knocked the wind and whatever else right out of me. Never found mine, it's in 18 feet of water somewhere between 2 and 3 ball heading west.

[Wish]

Wow. Good to know. Buddy of mine has a Phantom and rides it occationally. Will let him know. Thanks!!

[Wayne]

@Horton what made the fins ski so great?

[Horton]

@wayne softer flex and thinner

[A_B]

Warren Witherall was playing around with a fiberglass fin in late 80's with no holes. I pulled him into mid-39 on it, mounted in an HO Extreme. He said he liked the extra flex but he too was having a breakage problem.

[Horton]

https://web.archive.org/web/20040803001300/http://www.carbonfins.com/TheDiff04.htm

[Horton]

The above link is a an archive. CarbonFins closed down a number of years ago.

[MattP]

@Horton I'm glad your website building skills have improved since those days... All Praise Joomla!

[Horton]

@mattp you were in grade school when I built CarbonFins

[MattP]

@Horton and I was building websites in grade school... I could have been your developer back then. Now that's a scary thought. Carbon fin era I'm pretty sure I was in Middle School.. but I digress.

 

I just had a scary flash back to dial up. I'm sure I'll have a nighmare with that tone in it tonight.

[gator1]

@horton, how thick were those super duper aluminum fins that broke?

[Horton]

@gator1

.085 ish

the issue was not just the thickness but also the alloy and the way they fit in the fin slot

[gator1]

@Horton: The picture shows a fatigue failure at the junction of the fin and clamping mechanism. The mechanics are such that a thinner, more flexible fin would be exhibiting that bend at the junction.

 

Do you think the improvement in performance associated with a thinner more flexible alloy was from the fin essentially "hinging" at the junction where it broke, or due to an increased curvature of the fin as it bent over its entire surface?

[doonez]

I see some fin experiments coming @gator1

[gator1]

@doonez: Ya, about 2 am this morning it was all over except the cutting, milling, tigging, and crashing. @Horton's answer on "warp" vs "hinge" will set the direction. But either way its gonna be wild.

 

I've still got the fin and fin block left over from the Prophecy I ran over in my truck, so at least I'll start out with $0 invested.

 

And I hate messing with my fin. Fricking BOS is gonna kill me.

[Horton]

@gator1

 

With some older skis the fin had room to move side to side in the slot. This allowed for more flex.

 

I wrote this in 2003:

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.

 

I believe my CarbonFins worked so well 10 years ago because skis were not as precise as they are today. HO and D3 factory skiers used my fins a lot. Today I can not imagine using one of my fins in a new ski. I believe that the positive traits of the softer flex fins have been built into the skis themselves. To put it another way, the fins were covering up problems in the ski design and that is no longer necessary.

[The_MS]

The 106 carbon fin was awesome. @Horton PM me if you have another 106 laying around, I need it for my Monza

[Horton]

@ms

I do not think there is anything but scrap left.

[gator1]

@Horton, thanks.

[jlittle]

@gator1 I have a carbon fin you can try @Horton built way back when. I'll have to dig it out and find out what it is. I think it's an 88 but it might be a 106. Are those numbers correct? And how would I tell if it's not written on the blade?

[gator1]

@jlittle: Cool! thanks! What's your take: was it hinging at the clamp or bending into an arc over its surface area?

[jlittle]

@gator1 Don't know the answer to your question. I never pushed on it hard enough to see where it might have hinged at. But we should mount it up and give it a flex test.

[Horton]

The hinge point is about fit in the fin box.

[gator1]

The box on my prophecy is about .007 wider than the fin. This means the fin flops around about .o30 side to side at deepest part if it is unclamped. If the box is acting like an ersatz clamping mechanism, (I think this is what you're saying @horton) I'd have thought the fin freaks would have been obsessing about box clearance. Maybe .030 side to side doesn't matter.....

 

Also, moving the hinge point from bottom of clamp to bottom surface of ski stiffens the fin, and spreads the stress from the bottom edge of the clamp to the bottom edge of the ski once the fin has hinged to the point it contacts the ski.

 

But, my fin was biased up against one side of the box. This means for .060 of travel at the deepest edge, the fin is less stiff as is bends to contact the side of the box, then stiffer once the hinge point moves from the clamp to the surface of the ski. This means on my weak side turn, I have a two radius turn built into my ski. HORROR!

 

If .030 matters, this is all very mechanically interesting. If it doesn't, don't give a damn. If varying flex of a fin matters on a modern ski, same statement holds.

 

If PRP works on the various faulty parts of my back knee and I get to ski again, now that gatormod is finished for both fogman/stealth and powershell/dualok, screwing around with fin flex seems like a pretty good way to distract myself from my plateaued performance.

 

p.s. for all you MIT and Stanford engineer types, U of I did teach me the proper terms for all this.

[Horton]

@gator1

The Connelly fin is stiff enough that it does not matter.

 

I do not know how you get from .007 to .030 but .007 is plenty snug.

[gator1]

@Horton

Connelly fin sure feels plenty stiff.

 

Its a lever. .007" movement side to side at the running surface of the fin box, which is .038" from the fulcrum (bottom edge of fin clamp)results in over .030 at the bottom of the fin.

[ForrestGump]

Who was it who's fin fell out of their ski as the #1 seed at a regionals or nationals about 15 years ago and had a huge crash on their opener? Was that Mike Morgan? Or Forest Fisher?