View Full Version : too long fin
2nd May 2007, 03:43 AM
Purely hypothetical: what would happen if you stick in a fin that is 'too' long for your board? We know the effect of a fin that is to short for the board in comparison with the sail you're using but what if the fin is too long in comparison to board and sail?
2nd May 2007, 04:25 AM
Severalthings will occur if you use a fin that's too long for the tail width and footstrap offset of your board.
First, the board will be hard to control at speed.
Why? Without the requisite footstrap offset, where you have good leverage and control of the attitude of your fin, you won't be able to control the attitude of your fin very well and other control issues (tailwalking, spin out) will occur.
Next, there is the issue of speed.
Too much fin is slow, as it's just added drag.
Combine this with inability to control the fin and you go even slower yet.
But this is not only about the length (span) of your fin, but you can also install a fin that's too wide (front to back, or the chord length)
and this fin, while it's about the right length, will have too much power
and since these wide chord fins are usually a thick foil as well, they just aren't very fast because they have too much area.
But they do solve the depth issues for some sailors.
If you have way too much fin for the size of your rig, then getting planing will be difficult due to the drag issues.
There are some other balance issues (rig size vs tailwidth vs fin size) as well.
Hope this helps,
2nd May 2007, 03:18 PM
for rough estimation the correct fin lenght is 4 to 8cm shorter than the one foot off tail width to have the correct leverage as Roger mentioned. Thats correct for slalom boards. For the new formulas we are limited to 70cm fins and the one foot board widht is 81cm and more. So we need this season very powerful fins to compensate the lenght differenz to reach a goos lever.
3rd May 2007, 03:31 AM
Sounds reasonably logical. I had suspected the drag problems but i was somewhat offset by the principle of lift that a fin gives to a board. I struggled with the idea wether it would overplane and thus not plane at all or wether you just loose all stability and go to finsurfing rather than boardsurfing once you get in plane. Problem solved i suppose :d
And thanks for the trick Peter, but i never had problems with chosing my fins. It's just, i wondered because i already own a select Ride 40 for one of my boards, but i've resently bought a mistral flow 284 (113 L) for which i suspect it to be too big as the recommended finrange is up to about 37, 38 max really, seeing as the standard fin is 31 cm. My 40 would be too long, i just didn't know the effect it might have on the board. Never really intended on testing it though :d
3rd May 2007, 07:40 PM
There's also the trouble you can have with sandbars and shallow water.
3rd May 2007, 10:12 PM
also, try not to smoke epoxy dust
4th May 2007, 03:07 AM
also, try not to smoke epoxy dust
What kind of comment is that?
5th May 2007, 06:38 PM
Probably you may smoke epoxy dust when sanding your fin after shocking it in shallow water. On slalom/freeride boards, I use fins up to ~2 cm above the OFO without too many control issues. This is valid for the lower wind range. When overpowered, the board starts wheeling and I have to go down in size. However, this is not only a matter of length : I remember a 31 cm carbon fin very thick and stiff which was almost unmanageable on every board.
7th May 2007, 09:18 PM
Roger, when it comes to this statement of yours >>while it's about the right length, it will have too much power and since these wide chord fins are usually a thick foil as well, they just aren't very fast because they have too much area.<< What do you see as the distinction between power and speed? Are you stating that a thicker foil will have a reduced speed when comparing two fins where the area of the cord is the same if the area of the cord is maxed for the board? I do find that Pfaffi's rule of them has plenty of exceptions when it comes to my usage of fins.
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