My fin has a musical note it hits at terminal velocity somewhere between C and G and in one of two octaves depending on speed.
Pretty cool I know but does anyone know what causes this and how to stop it.
I have tried sanding the trailing edge with no success.
Check entire foil, from leading edge, to sides.
Check the base for flat spots across water flow.
Has to look and feel like a factory fin.
Did you glass it on with enough rope?
Hey Lee, Im getting this out of a fin that was moulded and has a true aerofoil. Sitting in a fin box, not glassed on.
Those are always the worst!
Anything CAD designed is bound to humm or really draggy.
First of all, take the seam off it, around the whole outline, then with 400, sand in the direction of water flow.
At the leading edge to thick point, sand with 220 in the direction of water flow.
Make sure trailing edge is even and NOT pointed, try to square it off with 600 to a tiny, can’t cut you bevel.
Should be NO sharpness at the leading edge, but almost.
Oh, check fin fit when loaded, by bending the fin slightly with your hands, to see if it’s seated flush with the board, and whether the mounting it tight.
My fin has a musical note it hits at terminal velocity somewhere between C and G and in one of two octaves depending on speed. Pretty cool I know but does anyone know what causes this and how to stop it.I have tried sanding the trailing edge with no success.
If the trailing edge is too thick, the fin will hum. It needs to smoothly taper to a thickness a little less than a millimeter.
If there is a bump on the trailing edge, the fin will hum.
If there is a leading edge bump, the fin will whistle.
Truth be known the reason the fin is humming is because it does not know the words to the song.
That said you are being led down the right trail.
I made a longboard once and put on a homemade fin made of plexiglass.It was real flexible and hummed like a Bee when I got up to speed.I rode it all summer and then filed the back.The hum was gone but it did not ride as good.Go figure.Heck the best shortboard I ever had was twisted like a pretzel and totally magic.What does this tell us about board design?
Hey cleanlines, better yet is the glass half full or half empy. What does this tell us about your surfing? Just kiding. I have a Lance Carson that only on some waves the fin would sing like a raped rabbit. It did not seem to have anything to do with speed but more the shape of the wave. I did have it fixed and I’m still riding that board it is my every day board. Love it.
Howdy Bagman.Where you been?Anyway that twisted board was made in 1972 from a Brewer blank.It was 6’10,flat deck diamond tail single fin with a beak nose and down rails.It looked like propellor it was twisted so bad and only rode left.I was on the north shore that year.Jim Turner rode it and it took me a week to get it back from the Lightning Bolt Boys.We were all going nuts trying to figure out how to build twisted boards.I wonder if you could program one of them there fancy assed shaping machines to make a twisted board?? RB
HaY RB I’ve been in surfers hell, can you spell Arkansas? My job pulls me out of Santa Cruz at least 2 weeks out of the month. I still check into swaylocks but there has not been a lot to respond to. The other question Yes for sure the 3 axs machine can make anything there is enough foam to make. Set up the board that you like, say a twisted 6’10 pin tail. Put a 10’4 " walker blank in there and stand back because the foam dust will fly. Now the problem is to find someone that can, finish off the board, not look at it and not try and make it strate, or say what the hell happen here? Making soming that flows is easy making some that jerks is not all that easy.
Is there any real reason to remove the hum…???..
I like my foils to sing- not humm
I guess…bad foil + humm. Humm = sideways vibration of the board. Vibration has to effect speed of the board. Vibration causes the rope around glass-ons to crack. Crack no good. Vibration causes fins to delam. No good. Vibration causes finbox to loosen…
At the very least it indicates cavitation and disturbed flow off the fin trailing edge - the board is surely better without it.
I’ve made a lot of bad fins learning how to make decent ones, and not one of them has hummed…each one, even the ugly ones, had pretty thin trailing edges to promote flow re-attachment.
Fins bend and move and oscillate far more than most people realize. I set up rotating fins stiff enough that I really need to push em to get em to rotate. Then, I can push on em by hand and see how far they move.
Then, go to a board with rigid fins and push on the fins equally hard to get an idea of what is going on…often it is pretty ugly.