Fin Theory

We surfed The Hook yesterday and got a chance to surf a twinzer with these fins.

The fins have a small cutaway at the base, the theory is that there fins produce turblulance and the cutaway releases that turbulance earlier and keeps the water attached to the fin.

The tips of the main fins flexed a bit, not floppy like a noodle, but flexed when you pushed on it. The theory is that the tip of the fin will conform to the water flow in hard turns and thereby keep the water attached longer.

With the stiff injection molded fins we use, by contrast, the tips of the fins tend to plow through the water creating drag and reducing the projection out of turns.

The last thing is that these fins were thick. The leading edge was doubled foiled, and the inside had a slight concave. The concave inside the foil reduces the pressure somewhat on the inside or high pressure side, that reduces the lift, but tends to allow the fins to break loose easier/quicker.

These fins are several layers of laminated carbon. The lamination schedule allows the fins to flex at the tip, while remaining stiff down at the base. The Carbon provided a very quick response, another version in fiberglass and epoxy was mellower, better suited for surface style tricks.

and how did they ride , cant wait to do a c5 set up , if my jig comes in today then i will install a set in my quad that will get lammed on sunday.

Very well, amazingly so. Be sure to post up pic's Mark, you're holding out, 'bro!

Thinking out loud and posting the results of my laborious testing I'm stealing a concept from aviation design, to increase lift in a wing either increase wing area or camber or both. So to make our wakesurf fins more effective at low speeds we have to increase the size. That way when we turn there is more area to push against the water and work with.

To test the theory I flew my hand out the window of my car. Fin design is HARD WORK! Going down the freeway at 65mph my hand would surf or fly all over the place. I had a ton of control. I was going fast enough to angle my hand and have it plane up and down on the wind. When the speed dropped down to 10mph, as I idled through the parking lot of my office, I had no control. The angle of my hand had no discernible effect on direction changes.

Next, I taped a 1' x 1' square piece of 1/4 plywood to my hand (What?! You don't normally do this? ) All the control came back at 10mph. I was able to air surf my hand/plywood combination at the lower speeds.

My thought has always been that fins create drag, that isn't really accurate, it's misleading, fins create control.

In theory, I would summarize: small waves big fins, big waves small fins. BIG in this context can be area OR camber as the aviation folks know.

(Message edited by surfdad on July 25, 2008)

Thats sounds like some pretty scientific testing you've done there Jeff

I have been looking into getting that twinser setup on a board. Its been interesting to read about this in the last few threads that its been brought up in. Seems like a good idea and sounds like it works too. Thanks for more input!

Love it Jeff! Nice testing!

Interested to see how the fins were set up on the board you tried. I'm assuming they weren't placed like the board pictured above... but you always surprise us...

LOL hahahaha, I could not do that test on my bike so thanks for the testing info . I have a couple new shapes , a 4.6" sorta like the shape that Jeff likes to make and a 5.6" x 22" fat nose board for the bigger/cruiser people. Sunday i should have enough time to get the top lam job on the 4.0 and the 4.8 boards " if im not hung out"

ok , c5 install kit just got here , the 4.8 will get c5 fins and maybe the 5.1 after i ride it saturday

Yep TXSurf, pure analytical bliss. There is something about the folks that have offices around here though, they don't seem to understand or appreciate science - you'd think that driving around a parking lot with your arm hanging out and plywood attached would resonate with folks that research was underway. Instead, they just look at me (more) funny.

Hey Matt, the board we rode was in the ocean, an 8 foot twinzer and it was set up just like Jobson documented. Rich Sanders is foiling us two sets for behind the boat, and I have a build in progress to more closely emulate a true twinzer. As soon as I get the behind the boat fins, I'll post up.

Hey Mark, any 'ol time you need some research done, you can count on me to publish it - I'm still looking for peer review on my findings, here though.

Jeff , looking for proper p[lacement for the c-5 fins , i did not install them on the quad , because i had no pics of any boards to try to set them up , i did lam the top deck. I rode the 5.0 board with the square tail it was super fast , i ended up with 375 fins from the vector quad set , any bigger had too much drive. My camera is on the blink , so i will try to get some pics soon and also using wax instead of traction sux

Hey Mark,

I'm hesitant to give you placement info because I literally made about 15 adjustments before finding one that worked, when I transferred that placement to a different board outline THAT second board sucked out loud.

It seems that all quad's or twinzers are very particular about the fin placement.

I'll share with you the guidance that Rusty gave folks and this is what I followed:

http://business.transworld.net/1999/04/

I copied the pertinent info from the article above. Pay particular attention to the one recommended point - it's very counter intuitive: "Â Try the small fins angled out slightly more than the main fins."

Through all the design and experimentation, the following are key points and suggestions (not guidelines) from Rusty that shapers might want to use:

 Ride an inch or two shorter than your regular shortboard.

 Pull the wide point back an inch or two.

 Make the back half of the board 1/4 to 1/2 inch wider.

 Cluster the main fins a little (1/4 to 1/2 inch) closer.

 Place the little fins so that they have a slight overlap with the main fins.

 The rear of the small fin should roughly split the distance from the rail to the main fin.

 Try the small fins angled out slightly more than the main fins.

 Try the small fins pointing to approximately the same place as the main fins.

 Try the main fins slightly smaller than you would normally ride.

 The twinzer-style fin lends to more vertical surfing.

 The half-moon fin has a drivier, down-the-line feeling.

Jeff thanks ,
i was going to angle them in some just did not know about overlap on the front fins

Mark, there are two...or maybe three workable theories in here. The Twinzer like on the board in that first picture. Those two fins work together more in concert than the C-5 arrangement that I am using, but it also changes the way the board rides - turns are wider...more drawn out. Another is from a five fin Bonzer, which the C-5 took some inspiration...then of course the C-5 that Rusty created. You'd be well served to research the 5 fin Bonzer and the Twinzer as created by Jobson.

i checked out moonlight glassing on the bonzer fin set up and boards by jobson , i already have an account with f/f and like i said one time before , its all in the r&d. so i will install them on the other 4.8 core i have not touched yet. i saw that twp uses only the c5 one a board they sell , that board must be fast & loose.

Actually TWP abanonded that and now uses strictly the Futures Rail boxes on the Composite X line. I think that Walzer is the only wakesurf manufacturer that is using the C-5 boxes, they were also the first.

Then WO needs to update their site. I rode a cwb ride over the weekend , stiff and heavy i could not flick it about

Just for fun tell me whats going on with this fin marked as "G"?

http://farm3.static.flickr.com/2132/2150371319_aef8be0fdc_b.jpg

Wow Petr -- that is really wild!
Nice cutouts on that one.

aha cause I am lazy and dont read comments form this page http://www.surfysurfy.net/2008/01/center-box-options.html?showComment=1199819640000

G. Early 1970's "Feather Fin" with slot cuts, (my Dad's previous all time favorite fin).

My understanding of the slotted or feathered fins was the same as holes. The holes, I believe came first. The idea was to reduce base area while increasing fin depth at the same time. I believe the consensus was they work, but not without some pitfalls. They allow the board to break loose easier, but at times especially in bigger surf they tend to be too "drifty." The holes were also supposed to help reduce outboard drag/turbulence which they did in small surf, but in larger or faster surf they caused more turbulence than a standard fin, so most everyone dumped the idea. Behind the boat, we don't really have bigger/faster surf/waves.

Sloted or feathered fins were built on the same theories, as well as cutaways but the same is true with these types of fins with the notable exception that the feathered fins also added some flex to the fins.

What is interesting to me is that many of the concepts for fins have been abandonded because they don't work well in big, powerful or fast surf and THESE are the attributes that we behind the boat are interested in.

Thanx Jeff you knowledge is amazing I am stoked.
Interesting is that they say that thouse safe fins (Pro... something, can't remember the name) with softer edge works better than stiff ones, probably because of less turbulence I guess.

Here is truly sweet DIY thread about bamboo fins. Enjoy builders
http://www.swaylocks.com/forum/gforum.cgi?do=post_view_flat;post=363496;page=1;sb =post_latest_reply;so=ASC;mh=25;guest=19463777

he he most craziest fin system in the world (xcept 10 fin boards or so)

FIN HEAVEN

http://www.surfresearch.com.au/f.html

(Message edited by hawaj on July 29, 2008)

I have a turbo tunnel in our longboard - we tried this board with 7 fins - it would ONLY go straight, but it did THAT really well.

http://www.shredda.com