fin hummmmm

Hey I just bought a board off the rack and the glass on fins hum horribly, anyone have any helpful ideas. The fins are those aercor™ fins so I don’t know how far I can go if I need to re foil the fins. Thanks, Dave

Hi Dave, Without seeing them it’s pretty hard to solve your problem. But here are two ideas to kick around. Wide base fins tend to produce more turbulance than narrow base fins. If the base isn’t foiled properly particularly at the trailing edge it will hum. Some fins just aren’t make to go fast and thus are unsuitable for boards that do. I know this is probably of small help. If you want to contact me feel free. Maybe we can exchange a few e-mails and solve your problem. Flat spots in the foil, too much cant or toe in can be a problem as well. Mahalo, Rich

…re-sand with 320 grit the back edges of the fin(trailing edges).there’s a bead on them,ESPECIALLY the base area.Herb

Listen to Herb, he has it right. If they still hum after that take the same sandpaper and soften the leading edge, just a bit.

…I was in a hurry, Seems my wife neglected to pick-up my youngest daughter.So as I was reading the first post of this thread,I received a phone call from a slightly comcerned care provider.In short I didn’t read your post til’ now,Sorry.Herb

Hey Herb, No apology necessary buddy – it’s mackin’ up here! Gone Surfin’, Rich

Thanks guys, I’ll give it a go, you see I never thought that buying a $500 Al Merrick Black Beauty would end up with such verocious fin hum. I tried contacting Channel Islands directly with no responce what so ever so I found Swaylocks, and now I received help imediately THANKS. I’ll check out the “bead” on the trail edge and do a little trial and error. My main concerns were sanding through to the core of the fins, my next solution was to bring it to my local glass factory and replace the fins with a removeable system. Thanks guys Dave

Ok you guys, here’s one for ya. I used to have a 7’2" mini mal shape with a real squared off tail and glassed thruster fin set up. When ever it got going real fast, it would whistle when you bottom turned. No whistle while trimming or cutting back, and no humming anytime. I sanded the back of the fins and it made no difference!!! Newbs

…Newbs, Most likely the leading edge(as Greg mentioned)was the cause of the whistle.If the leading edge is sharp it will cause a high speed whistle(like in full bottom turns),but not a hum as you mentioned.This is because the sharp leading edge will cavate at high speeds,especially in a narrowing radius.Solution…Sand it…urrr… you know.Herb

Herb; The guy I sold it to just brought it in and the fins are fairly dull up front…no bead either. BUT the outside fins have very little toe-in and only a 3 degree cant. Could that be it? It’s a great lookin’ stick, Larry Mabile did it for Gordon and Smith back about 15 years ago. Sort of a scaled down Phil Edwards shape. Soft rails with a heap of v in front of the fins and trailing off the tail. Can’t remember why I sold it…

For a shape like that you might consider riding the board as single fin. R.B.

…Naw,that shouldn’t cause a whistle. …W/O seeing it, I can’t say at this point. Is the foil on the fins thick(especially at the leading/trailing edges?)? …I had a gun with glass on tris back in the 80s(thruster pintail).The fins on it worked perfectly. …After the El Nino storms of the mid 80s past on,I shelved the board til the 90 El Ninos. …When I took it out of mothballs in 91’,and rode it, for some stupid reason the fins hummed,and whistled.So,I took it home and took a close examination of the fins. …Seemed that my inside fin as well as my center were canted in on the tips with a bit of twist to them(slight,not noticible unless you looked close).You see I stored it on it’s nose with the rail leaning up against the wall.It sat like this for years,and created warped fins…no big deal,I just heated them up and straighten them out.No more Music. …In you case I would say it’s somewhere in the foil.In any case,it sounds like a good stick!Herb

you ever look at someones face thats paddling out as you go humming by? its one of the best things ive ever seen…so i keep the hum. haha http://members.cox.net/austinsurfboards

my suspicions are your board has reached a resonant mode for the particular wave conditions you heard the hum. One thing you can do is increase the hydrodynamic damping. Another is switch out your fin to another type fin if it reall drives you nuts. Another solution is to be patient and try the board in other wave conditions. I have had a tri-fin hum on me under certain conditions, which I think was due to vortex shedding off the trailing edge of the side fins thereby inducining the vibes - but on many other days, this would not occur. I think probably, the bottom line is to learn to love the humm and don’t worry about it so much. chill brah.

You guys have it all wrong. I had a 1978 MR. It did the same, however it had box fins. A lot of box fin boards of today hum. Here is the problem: No foil on the inside with no radius at the base. Why humming on your glass ons, because there is not enough cant and because those fins don’t have enough bead at the base. More of todays modern boards with boxes would also hum, but the have enough cant to utilize the outside fin foil to prevent the fin from humming. One big point, humming does not mean your fins are set or glassed wrong. Some of my best boards hummed.

Fins hum because they dont know the words!

Well there has been some differing feedback on what to do about the hummmmm. First I just want to point out for the record that the first few responses (sanding the leading and trail edges) worked well. My main worry was just how far I could go before gouging the core on these fins. As for the radius at the base of the fin, I have been riding my boards with FCS almost since they came out and NOT ONE OF THEM hummed. Next I have had many, many boards with glass-on fins that did hum, nearly all were able to stop the hum with some re-foiling of the fins. I even had a board in the eighties that I ended up remove the foam from the rail side of them then re-lamming them which also worked. A couple of years ago while in Australia I had the honor of chatting with an old legend by the name of Chris Brock, he has been manufacturing the “Star Fin” or “winged keel” that Cheyne Horan made famous in the eighties/early nineties. While purchasing a couple of fins he explained that in most of the molded fins today, the trailing edge of the fin tends to have a tiny bead that often results in fin hum. He showed me how to remove this bead simply by scraping the trail edge with a razor blade. Oh and by the way I may still have the fins replaced with FCS for travel purposes. Also I likened the sound of my ever humming fins to Formula One race cars for their high pitched screaming. I even had one guy drop in on me who could hear them scream from a pretty good distance away. THANK GOD FOR SWAYLOCK I’ve been a “back yard” shaper in Manhattan beach for over ten years now doing it for the love of surfboards and the fun I see on my friends faces when they ride my equipment, so I’ll also thank those who are not mindless drones and will buy boards for reasons other than the label that appears on them. Dave Babylon Surfboards

try dragging a razor on the rear flat foiled surface from the base to the tip(repeat several times) putting more pressure at the trailing edge where the bead would be(whew). the bead will be revealed if its there. continue until bead is gone. the flat surface of the razor doesn’t flow with the bead like sandpaper, it just cuts the bead.