I have noticed two boards of mine that once they hit a certain speed, vibrate and then decelerate (9’+ boards). I feel the vibration and I’m not sure if it’s the fin or from the bottom contours. Both boards that have done this to me have rounded bottoms and were made in the 60’s. I’ve noticed this happening while I’m standing in the middle of the board and it’s usually in a steeper section (I can almost hear it as well as feel it). I’ll be going down the line, gaining speed then suddenly it hums and slows down. I’m hesitant to blame the fin since one of them has a huge, glassed on D fin while the other uses a 9.0 Fins Unlimited fin. The FU fin has been used multiple times in other boards without any vibration whatsoever. The best way I can describe the vibration is if you pushed very hard on a board and ran your finger along it to create a squeak, or vibration. Imagine that on a larger scale. I’ve checked the archives but not sure if I’m using the right terminology. Any help is appreciated.
Time for a new board? New ones don’t last as long as yours though… Mike
Your problem, is the fin. It’s a low frequency vibration. As soon as you feel the flattening of your speed, you MUST change direction, to keep gaining speed. Guess how I know this?
If you have other fins, try swapping it out with the FU fin. Is the box solid? Does the fin fit in there solid?
When my fins are bad I usually get a buzz when I do a hard turn. If the fin is to flexy, it can buzz when you go fast. I’ve had a couple of cheap plastic Dorsal brand fins that did that. If it’s a solid fin, you can try adjusting the foil with sandpaper. A bad foil with create more drag.
If you have too much belly in the bottom, and your rails are soft it can make the board slow. I’ve had boards like that, they’d top out in 2nd where others would have a 4th and 5th gear.
I had a couple of boards way back when that had that problem. Both were glass on fins. THe remedy was to sand the trailing edge a bit.
I think the fins were placed just slightly wrong and were cavitating. I remember hearing the same from others. Seemed to be a common affliction for glass on thrusters.
…hum or whistle problem is with the fin/s; front edge or back one, as mentioned you need to sand it and check. D fins do not work in most cases.
Thanks guys. The big D fin is a wooden glass on and it definitely can be foiled down on the trailing edge. That particular board also has the rounded bottom and very soft 50/50 rails. I’ll sand it down and see how that goes. The FU fin only vibrates on one particular board (G & S Hot Curl) and it fits in the box securely. That board has the rounded bottom with tighter, pinched rails. I did just notice recently that the front of the fin box has been cracked and will need a repair, so the entire box might have been vibrating. I’m going to fix the box and try other fins in it as well. The description of topping out in 2nd gear is spot on. Thanks for the help.
Fin hum. They hum because they don’t know the words.
Rear edge is too blunt, or there’s a bead of resin along it. Sandpaper fixes that.
Boards don’t hum. They’re mute.
Late 60’s had a mini gun that hummed while paddled, but not while riding. I had a soft railed board at Scorpion Bay, took off at 3rd point pumping hard off the tail, it slowed down really bad once I had hit top speed, I thought I had kelp caught on my leash, nope, maxed out the hull speed
Your 60’s era boards are in no way modern day progressive longboards. Expect them to be unrefined relics and maybe you will be surprised. I have had many a board chatter at places like Rincon, El Cap and various other Ranch and Santa Cruz locales. It’s a sweet thing to hear and feel. It usually means I am about to break the sound barrier. None of my boards ever slowed down though. Even the ones I didn’t Shape myself. Fin hum is a differant animal though. It can usually be silenced by simply sanding the fin.
I’ve grinded down the D fin into more of a speed fin shape and sanded down the trailing edge. I’m glassing it up now and will see what differences I feel.