What would cause fins to “vibrate”?
The board is a 5"7" retro fish with glassed on fins. The fins are 5.5" base by 5" depth toed in 1/8" and canted out about 3 degrees. I used two layers of 6 oz. glass on each side of the fin. Can I just put additional layers of glass on to stiffen it up a bit?
Howzit RandR, Are the fins vibrating or humming, check the trailing edge of the fins for a resin bead, that is the logical reason. Just sand the bead off. 2 layers of 6oz is plenty for the lay up on fins. Aloha, Kokua
All fins vibrate, whether you realize it or not.
Humming fins usually have a bump near the rear edge, or have a rear edge that is not tapered well/too thick.
Whistling fins usually have a leading edge bump.
Blakestah - can the fins be tuned to different notes?
Bolts from above!!! Is anyone else getting this???
Hmmmm...I can see it now...
Now appearing at the Royal Albert Hall Wave Pool -
The deep and melodious Requiem -
"Hey Brah, that's my wave"
starring the Hawaiian Symphony Surf quintet
featuring Laird Hamilton on lead whistling tow-in board
and the deep bass humming single fin stylings of
Bonga Perkins and Buffalo Keaulana.
Proud parents will be able to boast to the parents of overachieving scholarly type kids…
“My daughter surfs the lead humming fish in the Boston Symphony Surf Orchestra!!!”
And the tag line on all our literature?
“You’ll never hear Jimi Hendrix again - surfers rule!”
Now where did I put Zubie babies phone number? I know it’s around here someplace?
Blakestah - can the fins be tuned to different notes? ……
Well, I’m not Blakestah…but I couldn’t resist responding… Yes…one can change the pitch to some degree. Humming occurs when the frequency of eddy-shedding from a blunt body (which can be the trailing edge of a fin) matches one of the natural frequencies of vibration of the fin. For some background on the conditions necessary for, and the frequency of, eddy-shedding, see: Boundary Layer Theory. Herman Schlichting, McGraw-Hill Series in Mech. Engr. 4th Ed. 1960. Chapter II - Separation and Vortex Formation (p30-31). In short, the (3D) shape, dimensions, and structural stiffness of the fin, and the speed of the flow past the fin, determine both if humming will occur, and if so, at what frequency. The sailing center at UCSD used to have a sailboat whose rudder would hum. When hit by a gust on a reach, the humming would begin at a low pitch at a moderate (semi-planing) speed, and then both the the pitch and volume would increase as the boat speed further increased. Then just about the time the boat would accelerate onto a flat-out plane, the humming would (very) abruptly (and totally) stop. It was kind of neat as it gave the illusion of breaking the sound barrier. Conversely, the high pitch humming would abruptly begin again as you slowed down as the gust let up, reversing it’s earlier sequence.
Very cool MTB! One just for you…
When I was younger we would back-pack 8 miles into the Havasupai indian reservation and camp in the most beautiful area I’ve ever seen. There are three 100’ waterfalls and beautiful pools and trees and - man - it’s paradise. I even talked my wife into going for our honeymoon! Anyway the native teenage boys and girls and olders would be swimming and playing in the streams and you would see them pick-up a large rock and move it around a little bit and maybe they would go further downstream and move some more boulders around. When they were done swimming and playing they would sit on this one flat outcropping and just listen. I was very curious to what they were doing so when they finally got up and left I went and sat on their spot. My god! - they were tuning the gurgling and bubbling and whatever hundreds of sounds that the English language doesn’t have a word for so that they all arrived at that one spot as equally loud - and the canyon walls acted like an amphitheater!!! I’ve never looked at a stream or river the same since. I always try and listen for it’s unique tune. And the waves will sing to you also, if you just give them a listen.
i have a windsurfer fin that hum’s and the pitch changes with the speed, i love it!!
i’m sure i loose a little speed due to the energy being used for sound but it’s a blast sailing by someone with the board humming. On fast reaches the board will also vibrate.
bob
we got one wave , it doesnt really sing, it kinda growls ,FEEEEEED MEEEE BOOAAARDS,
on another note i once had a board and all 3 fins hummed at different pitches , then they would change pitch and volume with direction and speed changes…
it was such an annoying disturbance…never got any melody happening…
trailing edge to thick is the biggest culprit…
regards
BERT
MAYBE THE ANNOYING SOUND ITSELF BLED OFF ENERGY, BUT DID THE VIBRATION SLOW YOU DOWN?
We had a cool game board when we were kids that was a metal football field maybe 12" x 20" and my friend and I would set up our little football team in the positions that they supposedly should be in then plug it in and flip the switch. That sucker would hum and vibrate and the little men would start running around the field - SCORE!!!
After playing my guitar I would lay it so that it was face up on the bed and would strum it then place the pick on the strings. If I carefully put the pick on just the right spot - it would levitate for just a precious few seconds.
Hmmmm…
Levitation?
I’m no scientist, but what if you could use two smaller fins to induce vibrations that would roll over the bottom of the board???
My mind sees something but what???
What would happen at the board - water surface interface??? Mini vortex? Would the bottom of the board bounce off the surface of the water? (Like my pick levitated) If the board was just the right length and had the right vibration would it slap itself up off the surface of the wave??? (kind of like a hooked fish slapping on the surface for dear life) OR if you had smaller vibrational waves could you boost yourself out of the water enough for a benefit but still control??
A wicked funny thought … If vibration of the boards bottom turns out to be a good thing - and you could install a battery and vibrational unit into the board - I can just bet that the number of (satisfied) women surfers would “swell” into the millions, maybe billions! LOL
Should we be tuning our boards like those kids tuned their stream???
I’m just a graphic artist - these questions are for you…All I know is I couldn’t sleep at all last night - now I know why.
I think some people have been hitting the pakalolo late at night. 
Thanks for noticing cappio777 - Yeah - Vicodin will do that to you…
The real post is:
I shaped a fang tail (Michael Peterson?) that would sing/scream on a wave. It was retired after someone told me that he could hear it from the cliff at Salt Creek. When I was hidden in the tube - he said that it was like being at church and hearing an organic pipe organ. Hmmm…now I know why I wrote what I did.
Fin hum, trailing edge? all this time I thought it was because they didn’t know the words to the song. Live and learn thats what this site is all about.