I've just started running a Shapers 6.5'' DB Dolphin fin on my 10-6 Nalu.
It has loosened up the board nicely and I'm loving it more than ever now.
One thing I've noticed is when I get a bit of speed up (especially on bottom turns), it's making a harmonic whistling sound. After a bit of googling I discovered it is attributed to the trailing edge of the fin not being sharp enough. Most people recommend sanding it to get rid of the sound.
To be honest it doesn't really bother me (the sound), and razor sharp fins kind of scare me, but I'm just wondering if leaving it as is will be effecting performance/efficiency?
One of my favorite sounds, only happens when I am going flat out
on my board. Haven't tried to fix it on my board as I actually like it and I'm not racing anyone.
I thought it was the trailing edge of the fin being to sharp and that was resonating causing the high pitch whistling. On catamaran foils and aircraft control surfaces I ensure the trailing edge has a flat on it to stop any whistling/vibration.
Guess I will go and google it, should be an interesting read,
cheers,
Darryn
I've had a few boards with fins that whistle, but only when I'm going really fast. I actually like it, weird I know but I've sort of come to associate it with the adrenalin rush of racing across a fast wall. Also, sharp fins are nasty.
Hi JoffaDan. Sharpening fins? I'd rather the harmonic whistling sound, kinda cool.
Honestly don't want to be a smart ar5e but after receiving a nasty chop myself, and reading the following article, I'd be leaving fin sharpening to the pros on the big juice.
www.seabreeze.com.au/News/Stand%20Up%20Paddle/The-fin-chop-from-hell-Kai-Lennys-surfing-accident_7918038.aspx
I take the sharp edges off my kid's board fins with a bit of wet and dry, would hate them to end up looking like me!
Think of the sound as like a train whistle to warn others who might try to drop in on your wave
Can be coming more from fin positioning rather than side fin shape:
Whistle happens when fin positioning is across the main flow direction of the board, as a drag of high frequency when the planning reaction of board is more important than the fin foil reaction across the main flow.
I explain , except time it happens on short board going fast on extreme situation but in case of short board surfers use more fins areas than planning area of the tail shortboard , whistle did happen most of the time on big board like longboard or SUP.
Did happens to me longtime ago on 7'6" single fin but was obviously from a very very sharp fin. (got a large scare in my buttock from it)
Recently, i did wonder about it again when it happens on my 7'11" on rear fins of my quad set up made of TC aqualine . Those fins won't be bad construction . So This make thinking than positioning is the reason of whistling as well as trailing edge can be too.
Any feed back in this way
Fin whistle usually means there's a slight imperfection in the foil.
Try sanding down the trailing edge so that there's about a 45 degree angle all the way down.
Whistles happens then the point where the flows of water join at the back of the fin oscillates between two positions.
This happens typically when the trailing edge is square and the flow reattaches on either side of it.
The solution can be to have a sharp trailing edge (case 5 below), but in my opinion, it is too dangerous.
Better is to sand to round one side (case 7) so the one edge is favored to "anchor" the vortexes, trying to leave no cutting edge.
From Principles of Yacht Design (3rd edition), by Lars Larsson and Rolf E. Eliasson
Yep have to agree with colas's info
, I alway sand a radius into my trailing edges after I square them off, only takes a second and finishes the job nicely.
Good diagrams colas, I found similar info on the Farrier website, but yours are better,
cheers,
Darryn
Fin hum is a bummer; the vibrations cause drag, not to mention it's annoying as hell and a defect in a production fin. Take it back. I've tried refoiling hummers multiple times... not so easy.
Fin hum is a pain in the ass if you ask me. You start to wait for the hum rather than concentrating on enjoying a surf!
the wise and knowledgeable colas strikes again - always come out smarter after reading your posts.
