Fin Thickness

disland · May 3

How much does fin thickness matter. I had to replace a fin and I have two. One is .102 and the other is .95

What is the perfromance difference?

LeonL · May 3

I think I'd also be concerned about the fin(s) centering up in the slot.

bigtex2011 · May 3

thicker fins create more drag in my experience. you can tune that out with dft and length.

DW · May 3

As Horton will note - flex matters. Thinner = more flex which brings in some performance characteristic differences. Flex should make the fin feel a bit more forgiving. Opportunity to test both and report your findings.

Horton · May 3

@dw is correct that flex matters.

The bigger issue is drag. A thicker fin has more drag than a thinner fin. This may or may not be a bad thing because that drag creates stability. I have definitely experienced skis where I preferred a thicker fin.

On many modern fin blocks changing thickness can be problematic. They are often designed to clamp onto a specific thickness of fin.

Bruce_Butterfield · May 3

@disland the prior posters are all correct, but at your level I seriously doubt you will be able to tell a difference between those 2 in a fully blind test. Maybe if it was 0.102 to 0.080 or 0.070 you would be able to tell a difference, but it would be subtle. Pick the one that fits your fin block best and go ski.

I suspect I would have a hard time telling a difference between 0.102 and 0.095" in a fully blind test. That goes double for Horton!

disland · May 3

Thanks all, I found an old Goode fin and with some filing go it in the right place. I ordered a new one so its temporary anyway. This is all due to a parking lot incident that was a millisecond away from a $2500 problem.

Horton · May 4

@Bruce_Butterfield I'm pretty sure I could tell which is which between .095 vs .085 ( provided I was very familiar with the ski and could go back and forth)

RGilmore · May 4

One aspect no one has mentioned is, if your thick fin fits the slot in the ski "snuggly", then the thin one will not fit snuggle (duh). So the thick fin will be flexing over a shorter length - since it's anchored edge will be the bottom of the ski. On the other hand, with the thin fin it's anchored edge will be the bottom of the fin block, allowing flex over a greater length. Depending on the tail thickness, this difference alone could allow even more flex differential than the mere thickness difference between the two fins.

THEN, there's also the question of alloys - i.e., are both fins made of identical material, OR do they have different moduli of elasticity?

Bruce_Butterfield · May 4

@Horton yeah between a 0.095 and 0.085, most likely. But a 0.100 and 0.095? Call me skeptical.

But then we are talking about a 38off skier vs a 22/28 off skier.

Horton · May 4

agree. times I've noticed it is when I had spent a long time on the ski and then try a thinner fin

Horton · May 4

@RGilmore shhhh fin slot fit is one of my secret tidbits I only tell people what I'm trying to look smart.

DW · May 4

For those that feel additional drag from a fin thickness change, where do you think the drag is coming from? If you look at frontal area change of .010" over a 2.5" deep fin which is .025" square inches. That is probably not very significant relative to amount of ski in the water. Surface area remains constant if you do a simple fin swap. I have some thoughts but curious to what you guys think.

Horton · May 4

@dw It is not the thickness times depth. it is thickness times leading edge length plus the additional leading edges from the holes.

RGilmore · May 4

@Horton
I was attending a non-tournament waterski event at Bell Aqua in the mid-90's that involved Kris Lapoint, and I got to take a look at his then current ski. The only thing I remember about the ski is that he had filled the bottom gap around his fin with Bondo (autobody filler) and carefully smoothed it flush to the ski bottom. Took me years to fully understand what he was accomplishing with that mod.