Quad rear fins

[Badger]

For those with quads, what's everybody running for rear fins?

Flat foils, concave, 80/20, 50/50?

The waves where I ride are often slow and mushy although occasionally some spots get some speed to them.

I've been riding 50/50 rears for the past year on two different boards and liking them. My new Sunova Flow came with all flat foils and the board felt kind of stiff compared to what I'm used to. I have another 50/50 center fin on order so I can play around with different quad configurations. In the mean time I'll be using the thruster set up which I'm actually liking on this board.

I was just wondering what type of quad rear fins everyone else is using. Not the size, but what type of foil and why.

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[Bean]

Hey Badger, I was in search for quads a couple years ago and found a web based fin exchange program, Finatics out of FL.

https://finatic.com/ 

For a monthly fee $10-$25 you can test quads from FCS, Futures, Creatures Fins, 3D Fins, Gorilla Fins, Fin S and Rainbow.  That does leave a few good ones out of the mix however, but it might be a good start.

[supsurf-tw]

The great thing about fins is that you can totally dial in a board to suit your surfing style. That being said, I don't stick to a particular template or foil for rear fins. Every new board will go through several combos until I find the best setup. Much of the foil question will have to do with the toe in. The less toe, the more the inside surface is foiled. Straight  with no toe is foiled both sides.

[Beasho]

50/50

This is ONLY if you want Performance and Speed.

I have done extensive research, on-line, and by swapping out multiple fin sets on quads.  Add Aerospace engineering degree, geeky proclivity to figure things out, bags of fins to hot-swap in Pro-Boxes that I installed on my boards, flat foils out, flat foils in, asymmetric set up ( 3 double foiled, 1 flat foil facing 'wrong' way -- current favorite) . . .

Unless you are turning so hard that your outboard fin is coming OUT of the water you should be using double foiled fins.  Otherwise the opposing foils are adding significant drag.  There is some benefit to reducing spinout, because a flat sided fin has a greater resistance to stall, but this comes at a cost of increased drag WHEN THE FOILS ARE OPPOSING EACH OTHER ESPECIALLY AT HIGH SPEED.

Let the fireworks begin   

[mrbig]

 Beasho, Fssszztt - no fireworks 🎆! Am curious what your experience with IFT foiled rears was..

[Dooner]

Good advice here... I don't have a Flow yet, but I expect that Burt provided the correct fins for the intended use, I'm guessing his intention is to use the quad setup for extra hold and acceleration in very steep/barrelling waves and to use the thruster for most allaround conditions.  If you want to loosen it up as a quad, I'd recommend just trying out some smaller trailers. I think he puts the trailers near the rail and forward on that board, that normally indicates flat sided or 80/20 foil.

Quads are not all designed the same, there is a big range of trailer fin placement that will affect what fins or foils you want to use as well as the feel of the board. In general, the further back and closer to the stringer the trailers are, the more you want a 50/50 foil and the more smooth and carving the board will feel (closer to a thruster).
The more up and near the rail, the more you want an asymmetric foil and the board will feel more loose and swivelly (closer to a twin but with a lot more hold). As TW says, toe also comes into play, with more toe indicating a more asymmetric foil.

[Beasho]

A few good photos.

First from Swaylocks on the flow of the water up the board, and wave face.

Note: This shows where you would have 1 fin out of the water and therefore wouldn't be using the downwave foil "backwards" or otherwise inverted.

The fins job is to provide "Lift" and preven side slipping down the face of the wave.

[Beasho]

1) Toe in on the board defined: "Angled Inward"

2) Running an inverted airfoil, which is essentially like your thrusters in free flow (lower example).

3) Zero life angle of attack for various foils.

4) Airfoil designs.  Note the "Low Speed" design is what most fins look like, flat on one side. This is what a Cessna has to prevent stall at LOW speeds.  It sacrifices high drag, and speed potential, to prevent stalls when crashing during landings, which we experience as spin out.  In the air low speed is < 60 mph, in water @ 800 times the density this is more like 12 mph.  At higher speeds stall becomes less of an issue but then your dragging around an inverted Cessna airfoil:  Extremely Sub-Optimal     

[Dwight (DW)]

Honestly, nobody can answer this without seeing you surf.

As a shaper, I know how hard it is to recommend fins that suit "everyone". Just doesn't happen. So customers get what I surf and what my team riders surf.

[Badger]

This is all really great info.

My surfing isn't radical. I don't do any slashing off the lip or hard grinding cutbacks, yet. I just want a little more speed and still be able to carve some nice turns down the line.

The flat foiled quad fins that Bert chose for the Flow seem really big to me. Large 105's on the front and medium 94's on the back. The numbers relate to the intended weight of the rider in kilos. He believes stand up boards require bigger fins. I weigh only about 78 kilos. I get the feeling that these fins are intended for big fast barreling waves. My waves are often slow and small.

So I want to try putting the 94 flat foils on the front and running 94 50/50's on the back. All four fins the same size. This is about the same set up as what came with my JL World Wide 8'5 which seemed perfect on that board. I had to special order another 94 50/50 so it will be a few weeks before I can try it out.

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[Beasho]

This is all really great info. . .

My surfing isn't radical. I don't do any slashing off the lip or hard grinding cutbacks, yet. I just want a little more speed and still be able to carve some nice turns down the line.

The flat foiled quad fins that Bert chose for the Flow seem really big to me. . . .

I agree.  Most expensive glass fins felt too big.  I just kept sizing down until the board would spin-out unless I engaged the rail. 

We all DO surf differently, but I think that there are some universals that should evolve to the top. 

A Few Takeaways:

1) My first board I thought I outgrew until I realized that if I put my foot back IT WOULD TURN (see below)
2) SUP's ride higher than surfboards which are more like 'sinker' windsurfers and waterskis that can rely more heavily on rocker
3) A SUP mentor told me to start turning harder.   So I did.  My fin boxes started blowing out.  I replaced 5 of 6 forward boxes on 3 boards with Pro-Boxes.  Problem solved . . . NO!  Most recently I have had 3 of those boxes start to fail again.  I would like to think its related to my turning, but could be related to 2nd point.  Really frustrating. Have to get the router out again.

Most people will just surf what feels good.  I wanted to figure out what was happening.  Ironically it seems like no-one can explain what is really going on.  When you have two camps with opposite perspectives something eventually has to give.

DW has made a Zero Toe / Zero Cant board and reported he didn't like it. 

The JP guys seem to swear by them. 

So where does this leave us 

There was a thread related to this last year which went back and forth:

http://www.standupzone.com/forum/index.php/topic,26005.0.html

[anonsurfer]

For those with quads, what's everybody running for rear fins?

The waves where I ride are often slow and mushy although occasionally some spots get some speed to them.

I was just wondering what type of quad rear fins everyone else is using. Not the size, but what type of foil and why.

For slow and mushy waves I really like the Futures Blackstix fins (front and rear). They generate a ton of speed in slow waves.   These are my preferred fins in really small/slow conditions.

Lately I've been digging the Captain Fin CF Quad set.  Not quite as fast as the Blackstix but still lots of drive and the raked design helps make some nice drawn out turns.

[RATbeachrider]

FCSII Carver front (SM) and FCSII Performer rear (SM) ... mixing them up and liking it!

[supsurf-tw]

DW has made a Zero Toe / Zero Cant board and reported he didn't like it. 

The JP guys seem to swear by them. 

This comes down to personal preference and a lot of it has to do with the shape of the board itself. Zero toe\cant doesn't work on just any old board, it's another factor has to be figured into the overall design. It's a matter of compensation, just like rocker, outline, etc.

-TW

[OUTSIDEWAVE]

Hey beat why not do a little experiment You have the  tracer thing that calculates your speed and distance per wave  why not ride 10 waves  with the  fins set  up one way and then 10 more waves with  the fins set  another.   try 3 fins vs 4 fins etc.  I know no 2 waves are ever the same  but this might give a good quantitative  description to an otherwise subjective  evaluation. 
I experiment with fins all the time  for the longest time Though quads were the way to go and  to some extent I still do.  but I have on board that has a typical thruster set up and I find that I seem to get really good rides on that  board.    I have not ever  switched out fins in the middle of a session. 

I have all really enjoyed the  3d fins   with the flat foil on the tips   these seem to be the best system that I have ridden  wether it is 3 or 4 fins set up.