Author Topic: Which fin would be best?  (Read 2385 times)

Larry2c

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Which fin would be best?
« on: December 27, 2016, 04:18:01 PM »
Sorry if this is a double post - it looked like i got bumped off before it went out the first time and it isn't showing up so here goes...

I have searched a bit looking for info on fins and stability but nothing seems to hit the nail on the head for me so I'm just going to show a picture and ask. I'm going out tomorrow and I anticipate it will be windier than usual in the bay so plenty of chop. My SUP is an 11.0 Isle Flat Water Glide (didn't fully understand the FW designation when I bought it). I want to make the board as stable as possible and i have 2 fins. I've been using the Isle fin but as you can see, the other fin goes a couple inches deeper into the water but has a bit less total area.

Which one do you think would b more stable? I plan on trying them both but I just wondered what the experienced folks think about fin size & shape relative to stability. Thanks!

Picture won't show up for some reason - I'll get it to work somehow...
« Last Edit: December 27, 2016, 04:36:59 PM by Larry2c »

Zooport

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Re: Which fin would be best?
« Reply #1 on: December 27, 2016, 06:16:13 PM »
I think the longer fin will give you a little more stability.  Not sure if the difference will be noticeable.  Fins do a little, but, IMO, the main factor in stability is the width of the board and the flatness of the deck. 
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Badger

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Re: Which fin would be best?
« Reply #2 on: December 28, 2016, 04:30:45 AM »
I doubt the difference in stability will be very noticeable.

I'd go with the ISLE fin. It will be faster, track better, be weed free and have 2" less draft.

The dolphin fin might have an advantage if you plan on downwinding or surfing.

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mrbig

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Re: Which fin would be best?
« Reply #3 on: December 28, 2016, 05:34:39 AM »
As a guy who struggles with stability I respectfully disagree. The fin with the greatest amount of surface area and width will usually be more stable.

JB very stable for instance. All of the yoga specific fins are wide wide wide. The dolphin would be a much more surfy fin, but less inherently stable IMHO.

Longer thinner fins great for DW but are NOT as stable, they "hunt" in non windy choppy conditions..
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DavidJohn

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Re: Which fin would be best?
« Reply #4 on: December 28, 2016, 05:46:33 AM »
I'd be choosing the long (more dolphin shaped) one..

Wetstuff

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Re: Which fin would be best?
« Reply #5 on: December 28, 2016, 06:04:05 AM »
As another 'struggler'.. I tend to agree with both Badger: probably mostly mental ..and Bigs: more surface area.  Consider the fin without forward movement ..it's a paddle.  However, there's probably more lever-arm resistance the farther the tip of the fin is from the C/L.  (I prefer a shallow fin in the skinny water where I am)

Tell yourself; one fin is better than the other ..no coffee - bend your knees - never look down ..paddle hard.   In that chop, see if you can avoid spending much time at 45-90deg to the wind.  I don't think there has been a day when I felt like I was sitting in a recliner out there, but that is good - I think?

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yugi

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Re: Which fin would be best?
« Reply #6 on: December 28, 2016, 06:18:29 AM »
The deeper dolphin fin may make up for less surface area of the Isle - so stability may be close-ish. (deeper has more leverage which can make up for less surface area, as mentioned).

Your Isle fin looks like stronger tracking. Notice either fin placed further forward in the fin box will  track less and turn better.

You didnít say what your riding is. Which makes all the difference. My personal take would be to put the less tracking fin (dolphin) up front in the fin box so the board turns better. Then learn how to paddle straight by using proper technique. If you have poor paddle technique and rely on a fin for tracking you will be wasting a lot of your power. You also will have less incentive to progress. 

Turns are fun even on flat water. Fast and efficient in races are key to success. Practicing turns improves your board handling. My guess is the turnier option is also better for sidewinds.

Even if the Dolphin is slightly less stable I'd still go for that and improve your reactions. It is the instinctive reactions to instability that make SUP such a good workout. You definitely improve with time on water so do push yourself.

If you got a lot of weeds where you paddle, well, the choice becomes obvious.
« Last Edit: December 28, 2016, 06:40:02 AM by yugi »

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Re: Which fin would be best?
« Reply #7 on: December 28, 2016, 07:14:41 AM »
A fin with a lot of surface area can make a tippy/rolly board less so in some conditions. I've found that my relatively larger Gladiator fin makes raceboards less twitchy than their stock fins in flatwater and light chop, though it makes it more susceptible to roll and yaw when cutting across or diagonal to steep waves and larger chop. As you get more comfortable on a board and your adjustments to its response to disturbed water become more reflexive, the larger fin becomes less valuable in the smaller/calmer conditions where it initially helped, while remaining a hindrance crossing waves and chop.

yugi

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Re: Which fin would be best?
« Reply #8 on: December 28, 2016, 07:18:16 AM »
^ well said

burchas

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Re: Which fin would be best?
« Reply #9 on: December 28, 2016, 07:20:27 AM »
I would go with the stiffer fin out of both.
If the dolphin is stiffer, its stiffness and depth will compensate for the loss of surface area and shape.
The Isle fin looks inherently stiffer due to shape which is more optimized for you're looking for IMO.

From what you're describing flex in the fin is your enemy and will work against you.
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PonoBill

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Re: Which fin would be best?
« Reply #10 on: December 28, 2016, 08:47:50 AM »
Funny to read this, because with all the differing opinions I think everyone is right. For our purposes you can separate stability into two types (they both work the same way, but the separation is useful). Initial stability, which is the early part of the rolling, is helped by the area of the fin, both in resisting the roll statically and by the lift of the fin while it's moving through the water. So the big short fin works well.

Once the roll starts, the longer fin, with more area at the tip (the end of a lever arm), will slow the roll more and help you catch it. Almost as important, it will slow response to your correction, because perhaps as many as half the falls result from overcorrection.

the rake of the Isle fin, which looks sort of like an Allison Gladiator shape, will make the correction force a little more complicated, and might make the board pitch a little while it's rolling. But I can't say whether or not you'd feel that. Probably not since the fin is low aspect.

In reading the responses, I think every aspect of my answer, and a lot more, are already there and quite correct.

So the answer is--either will work, and they'll only be a little different, but you can get used to either one. Whatever feels best to you.
« Last Edit: December 28, 2016, 08:52:03 AM by PonoBill »
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Larry2c

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Re: Which fin would be best?
« Reply #11 on: December 29, 2016, 06:10:19 AM »
Well, the results of the test are pretty inconclusive. I went out yesterday with the Isle fin on the board and paddled for about an hour. Then I pulled out and installed the dolphin fin. By then the wind had died down quite a bit so I can't say whether there was any noticeable difference in stability. I will say that the increased depth made me walk out into deeper water to launch which is a bit of a pain when the water is cold (relative temperature knowing some folks here paddle in water that's almost freezing!)

Thanks for all the feedback and I'll try this again on another trip when I can get more consistent wind to test in.

By the way, I appreciate all the technical/in depth responses. I'm an NC Engineer and looking at my stability question from a physics perspective makes a lot of sense. At the same time yugi and others have stressed time on the board and challenging my body to get used to and react to instability is important. When I see somebody pull out on a race board in the same water I'm challenged by I push myself to keep going since they obviously are on a less stable platform than I am and they appear to have no issues. Like always, practice practice practice...
« Last Edit: December 29, 2016, 06:22:02 AM by Larry2c »

Eagle

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Re: Which fin would be best?
« Reply #12 on: December 29, 2016, 02:31:43 PM »
Would expect the stability difference to be quite subtle when just tipping side to side on flat.  If the overall area is about the same - then the stability sometimes feels about the same even though one is deeper and more narrow vs one shallower and wider.  The stability equation kinda gets offset in that situation looking at those 2 fins.

More noticeable should be the dolphin is easier to turn vs the isle easier to track straight.  The dolphin should be harder to stall and broach as well.  If the area was a lot different - then stability levels become much more noticeable.  ie.  my SIC 7.0 is quite a bit less stable vs my much bigger JL Tracker.
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Larry2c

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Re: Which fin would be best?
« Reply #13 on: December 29, 2016, 03:46:46 PM »
Thanks Eagle - what you say makes sense but I have a question on two terms you used. Stall and broach - planes stall and submarines broach but for a SUP I'm not sure how those terms apply. Can you clarify that for me? Thanks!

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Re: Which fin would be best?
« Reply #14 on: December 29, 2016, 05:46:25 PM »
Hi Larry - stall to me is when the fin starts to cavitate.  When on a wave either surfing across a wave on a SUP - or sailing a boat with an overly amount of heel angle - the fin or rudder starts to get bubbles around it.  It is a very distinct feeling.  On a board I feel the board slow and want to broach (or flip over).  When this happens you have a few seconds to correct the problem.  What I do is step back and weight the rail that wants to flip over and straighten the board down the wave vs across.  This eliminates the stall by re-attaching water flow around the fin - getting rid of the bubbles.  The board speeds up - and the wave behind stays behind or flows harmlessly by.

The time a stall and broach most often happens is when you go slower than the speed of the wave.  You should always try to be moving forward of the waves and jumping to the waves ahead.  You get zero stall and zero broach if you keep the board angled across and down waves properly.  With a small fin the wave pushing from behind slips by vs with a big fin it catches and flips you over.  Normally I feel a stall when surfing too much across a wave and not down enough.  Just power up down the wave and you should be good.  ;)
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