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#2898255 - 01/14/19 07:36 PM When changing fin size ?
Mat6920 Offline
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Can someone explain when and why you have to or it s better to change fin size based on wave size / tail size. Sometimes I hear ''you dont need as much fin'' or '' for big waves you need smaller fins''. I never really understood the theory behind that.

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#2898345 - 01/14/19 10:49 PM Re: When changing fin size ? [Re: Mat6920]
patrolman Online   content
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I have asked the same question.

My experience, that has been reaffirmed this last round of swell, is that in bigger waves you are going a lot faster. My sense is that my boards are not as loose at the higher speed. My analuysis is that with increased speed you increase water pressure on the fin, especially as you change the angle of attack (turn).

If you reduce fin area in larger surf you would keep the same pressure as the larger fin in smaller, slower surf. But then there is the question of chop. A lot of times bigger surf has some chop. And at higher speed you're more likely to lose control when you hit chop. So reducing fin area might be counterproductive in choppy conditions.

My 2 cents.

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#2898353 - 01/14/19 11:16 PM Re: When changing fin size ? [Re: patrolman]
Mat6920 Offline
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That might be a good reason actually ! but i would have thought that at greater speed you want control and having fins which sits deeper in the water is helping but your analyse seems to be valid. But on small waves, i would think that big fins would create more drag, therefore reducing speed. I dont know it s confusing !

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#2898359 - 01/15/19 12:05 AM Re: When changing fin size ? [Re: Mat6920]
freeride76 Offline
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it is confusing and maybe there are no set rules, just exceptions that individuals need to find for themselves.
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#2898402 - 01/15/19 02:15 AM Re: When changing fin size ? [Re: Mat6920]
tedshred Offline
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Another theory I've heard re small fins in bigger waves is that board design features for larger powerful waves (pin tail, knifey rails, channels, etc) add hold like a larger fin would thus don't need as large of a fin.

Personally that all gets too confusing so I use the same fin but change construction to keep it simple.

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#2898406 - 01/15/19 02:37 AM Re: When changing fin size ? [Re: Mat6920]
sd_101 Offline
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I agreee wirh whats said about decreasing fin area when youll be moving faster and have inherent speed from the wave especially as tail rocker is flattened out and you dont have the rail to initiate the turn as much. More tail rocker and you can get away with more fin.

Ive also found on those bigger fatter days, where a wide tail stubby will feel out of control on the bowls but the pin tail not enough drive through the flats, a nice medium is increasing fin area with a reduced tail area.

Took me a bit to figure out my gx round tail for my local, but found it worked great at some heavier beach breaks. Added fins that I usually use on the GX squash for fatter point beak waves and it did the trick.

Very minor changes in area. Like M/L down to M and back. Nothing all that drastic.

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#2898620 - 01/15/19 12:26 PM Re: When changing fin size ? [Re: Mat6920]
aldo1 Offline
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Smaller fins with more rail line for me.
For instance, riding a 5'11 VS Shadow with stiletto fins is perfect for me. Step up to my VS Time Machine at 6'4 with similar volume to the shadow and with the same setup it is inherently stiff, almost can't tun it. Reduce the size of the rears and voila..........back in business.

Longer boards equal smaller fin area for me in both small and big waves. Of course it depends on the shape of the board too. The above example is accurate because the boards have a similar shape.

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#2898656 - 01/15/19 01:07 PM Re: When changing fin size ? [Re: Mat6920]
Duffy Offline
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In waves above 8.24 feet (face height) with a hollowness factor of .75 or greater (lip is landing at least 75% of the way down the face) then youll need to reduce fin size by 12% for round pins, 8% for swallow tails and 4.674% for squash tails.
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#2898684 - 01/15/19 01:41 PM Re: When changing fin size ? [Re: Mat6920]
jkb Offline
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I go by tail width.

The wider the tail, the more fin area I use.

The narrower the tail, the less fin area I use.
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#2898725 - 01/15/19 02:27 PM Re: When changing fin size ? [Re: jkb]
SharkBoy Offline
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Originally Posted By: jkb
I go by tail width.

The wider the tail, the more fin area I use.

The narrower the tail, the less fin area I use.


agree with this but also how its breaking.
It can be big but facey, big and hollow, and each of those can also combine with how fast it's peeling.

fast hollow....quad
peaky hollow, thruster
big, mushy slow peeling ....way more fin
big and hollow less fin more rail

I reckon surf gets generalized by how high the waves are too much, small wave or big waves. there are so many variations.
Just compare head high trestles with head high jbay and look at the distances the pros are going in and between turns. The waves might be the same height, but they are moving and breaking differently and that reflects a lot on what sort of equipment is optimal. Compare Snapper to Bells, Bells to Jbay, Jbay to Trestles all at the same 4-6 feet. probably want the biggest fins at bells, the most upright fins at snappers, most rake at jbay


Edited by SharkBoy (01/15/19 02:31 PM)
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#2898804 - 01/15/19 04:20 PM Re: When changing fin size ? [Re: Mat6920]
tom@daumtooling Offline
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Fins preform two different functions. Directional control and kinetic propulsion. In more powerful waves directional control becomes more important and that is derived predominantly from foil. In soft weak waves kinetic propulsion becomes more important and that is helped by larger plane form. Foils become more efficient as the flow rate increases up to the point of ventilation. So, big clean faced waves don't require as big fins as smaller weaker waves. In big choppy conditions you might want to go with a deeper fin to reach down into cleaner water. But, when you need to pump for speed fins that grab and redirect more water per pump are more efficient than a finely foiled smaller plane form fin/fins.

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#2898824 - 01/15/19 04:48 PM Re: When changing fin size ? [Re: tom@daumtooling]
SharkBoy Offline
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Originally Posted By: tom@daumtooling
Fins preform two different functions. Directional control and kinetic propulsion. In more powerful waves directional control becomes more important and that is derived predominantly from foil. In soft weak waves kinetic propulsion becomes more important and that is helped by larger plane form. Foils become more efficient as the flow rate increases up to the point of ventilation. So, big clean faced waves don't require as big fins as smaller weaker waves. In big choppy conditions you might want to go with a deeper fin to reach down into cleaner water. But, when you need to pump for speed fins that grab and redirect more water per pump are more efficient than a finely foiled smaller plane form fin/fins.


bowdown
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#2898826 - 01/15/19 04:50 PM Re: When changing fin size ? [Re: Mat6920]
freeride76 Offline
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bowdown
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#2898935 - 01/15/19 08:49 PM Re: When changing fin size ? [Re: Mat6920]
Mat6920 Offline
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I dont know how accurate your theory is Tom but I ll buy that hahah. It s all pretty weird, my DX1 6'2 did not like the AM2 (large) when my CI Fever loved it and Fever has narrower tail. DX1 works super well with the new Joh John Medium. However i m buying the theory about the narrow tail like pin tail, it acts like a middle fin on its own. Smaller fins have easier release I found too.

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#2898954 - 01/15/19 09:48 PM Re: When changing fin size ? [Re: Mat6920]
aldo1 Offline
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Registered: 08/13/12
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Loc: Bahamas
That sounds right

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