what’s the best way, sharpening the trailing edges of fins or blunting them? my bamboo glass-on speed dialers are humming like mad! it sounds like i’m riding a Tie Fighter instead of a 5’10 fish!
kirk
Sharpening.
Futures have some advice on fixing humming fins somewhere on their site. Sorry don’t have a link.
They don’t know the words cause they were foiled that way.
Look for irregularities. Refine the trailing edge carefully with 150 grit and a block. Or use a half round bastard file.
Leading edges generally are the cause. Mass produced fins slip by on Q.C. sometimes.
Aloha, Rich
found it on the Futures site – thought i’d share:
Q: Whats the reason why fins sometimes hum?
A:
The short answer:
Pressure differences = Vortices or Turbulence = Vibration = Humming Fins
The long answer:
As
water flows around a fin there are different pressures on each side of
the fin. Water flows meet up at the trailing edge of the fin, and in
cases with very different pressures, vortices or turbulence can be
generated. These vortices push and pull on the trailing edge of the
fin, causing it to vibrate. This vibration creates pressure waves or
sound. Think of it as your voice when you blow air across your vocal
cords.
Have
you noticed that your fins hum at certain points while you are surfing,
for example during a bottom turn on a fast wave? The vibration hum can
be amplified or louder in cases of resonance. In fin terms resonance
happens when the pushing and pulling from the vortices causes the fins
trailing edge to move back and forth how it wants to move naturally. Or
more technically, resonance can be defined as the circumstance when the
force applied to the system is equal to the damping or resistance of
the system at the systems natural frequency.
How do you fix it?:
Sand
the sides of the trailing edge with a 100-150 grit sand paper (give it
a few passes) and then surf it, if it still hums then give it a few
more passes with the sand paper. The idea is to minimize the pressure
difference at the trailing edge by sanding off any imperfections that
may have been left from the production process. Make sure you don’t
sand too much, the more you sand, the sharper and more dangerous the
trailing edge gets.
…man, Im not Halcyon´ advocate, but why not listen him? he s a finmaker
so you was in need to go to a brand that say the same…
anyway, there s difference between hum or whistle
if the fin has kind of protuberance in the leading edge or the edge is too thick, it whistle
-also, Future seems to talk about thrusters cause I use the bonzer set up and I dont have hum in bottom turns
hahahaha… in my early high school days when I first started making boards we had a lot of fin hum. eventually we learned that the trailing edge had to be uncomfortably sharp not to hum. I have a nice scar on one shoulder from one such sharpened fin. Happened in a sharky spot, a good ways from shork, too.
You ought to have used the new search feature. this topic has come up a LOT, and a LONG time ago.
Molded fins usually have some irregularity all the way around the edge. Take a palm sized bit of 220 grit wet-dry out into the lineup with you and tell your buds that you’re fine tuning for the waves THAT DAY. Tell them yeah, it’s a humbug but you can gain five percent if you only tweak it just right for the conditions. And that a higher tide requires a slightly different foil, which only you know how to do, based on years of practice and wave channel testing data you acquired from a major manufacturer.
remember: you can’t catch fish if you don’t go fishing
yeah, what he said…
thanks, Rich. i did exactly what you said and now have a nice, sharp trailing edge on all four fins. will test ride this morning at the hook. stop by if you’re in the neighborhood! and thanks again!
kirk
Interesting topic and got me thinking about how I look at fins / foil shape in general. Ive only been playing with surfboards for a few years but have been racing sailboats for many years and sailboarded alot in the 80-90’s. I always worked hard at keeping any foil as fair and smooth as possible. I havent experienced any humming on a surfboard (yet) - maybe its because I wetsand and cleanup any fin I get. With sailboard fins - we also worked hard with FU boxes to get a really tight fit - often used mylar film between the fin and box to ensure no wobble or movement.
It may not directly apply to surf fins but for boat foils (keels, daggerboards, rudders, etc) we would foil the two sides to a thin squared off edge at the back edge - not pointed knife like edge but flat with hard corners. Imagine making a perfect knife edge and then block sanding the point off by making it flat - 90 degree to water flow. After that If we had any hum we would then put a slight angle on one side only - usually did the trick. Problem was the hum (if present) would only occurr at certain speeds - so it sometimes took time to repeat/find/fix.
The following link shows some tips from the Farrier Catamaran manual - pg 2 has a diagram that sort of shows the angled end bevel that Im talking about.
http://www.farriermarine.com/pdf/Hints.pdf
Again - Im just a new surfer and only provided this as an interesting comparison. I would definately take any assistance provided by the true sways experts here and run with it. I know I appreciate their assistance and apply it whenever I can.
Id be interested to hear about how it worked out.
yoyo
****
****
**
**
UPDATE:
after sharpening the trailing edges, i’m now running smooth and silent! thanks to everyone for the input!
kirk
Hey just on the fin hum discussion.Same end result as has been said but if the fins have been glossed,sometimes a slack polisher leaves a resin bead (from the gloss guy ) on the trailing edge.Cut back with a razor blade or sandpaper.Bingo ,no more hum
Fin hum comes from
A) rear edge of fin too thick
B) irregularity (resin bead) near rear edge of fin
C) fins that are too thin and flap in the breeze
It takes a different cure for each cause. Fins that whistle have a bead
near the front edge.
When sharpening rear fins, you should stop at a little under a mm thick if you do not
want to get unwanted cuts on your feet. Three quarters of a mm is generally thin enough
not to hum…
Correct on that one Blakestah.As you have indicated hum and whistle are similar(generally) but opposite.In my experience,hum is more prevalent.Yes ,foil can be the problem.If it’s professionally manufactured not generally a drama,but it does happen.Like you said if a fin is too thin at rear edge it can start to hum.and if at the beach easiest ,** in most cases**,simply rub the back (trailing) edge with something abrasive.Dull the rear edge is the deal. More often than not then go surfing.Sometimes but not often the fin will be too thick in the wrong places.Obviously needs some sanding back.maybe not so easy to do at the beach.Handy to carry a spare and do alterations later.
G’day Bubbles,
You’re not the infamous “Bubbles DeVere” by any chance?
If so, love your work.
No idea what I’m talking about?
Find “Little Britian” on Youtube.
Cracked me up cuttlefish.Funny as.The poms have really good comedy.Am sure she could keep a few of us warm at night.All at the same time.
Just a side note on fin hum though.Made 2 boards for 2 clients a few years back.Didn’t know each other and both were state level surfers.Each asked for FCS YU standard fins. No problem.Surfed their boards for a while then each purchased a set of YU carbon fins.Several weeks later both guys indicated that both their sets of carbons hummed badly.We checked them as best as we could.All edges were good.All we could see was that the centre section of foil was thicker than the standard sets.A mould problem.I made enquiries re; the problem but it never panned out.We stopped using and selling this model.
The K fins in carbon (the original K fins, not the K2.1’s) whistled like no tomorrow. I hear it was also a bad mold issue. I often surf near Casino Pier, which, at the time, had an old-school rollercoaster on it, and one day in mid-winter I swore that they must have fired it up and the tracks were screeching, but it was just me and my fins making the racket.
Just spoke to someone with Futures fins in his board who tried this advice and the problem is not going away. Is there anything else than can cause fin hum?
Sometimes if the fin is too thin and flexy it will hum. You need to stiffen it up.
But before you do that I would check the rear edge again for irregularities.
Just hack 'em off! The whole “fin” fad is on it’s way out now!