Multiple Fin and Adjustability

Back a few months ago we had the opportunity to test and ride the Walzer Pintail. I absolutely loved that board. James liked it also, but as he practices more skateboard style tricks - specifically a shuvit, there weaknesses of the twin fin design become prevalent.

If you read the Shred Stixx ads of last year Jerry would point out that more fin area would equate to more drive. When compared to a single trailing fin, that is typical on say a Telum or 4skim...the thruster design of a Stixxstreme is significantly greater.

The Walzer design is a twin fin. It had more drive than a Prop, Telum, etc. and less than a Stixxstreme or F-18 in standard configurations.
What it gave up in drive, it gained in loosness of the tail. surface 3's were alost automatic.

The one drawback is that while the Walzer had an outline that would allow it to be ridden revert (tail first) the outboard location of the fins caused the inside fin to catch in the wave.

Here is a picture of the underside of the Walzer Pintail.



As you can see in the above picture, the fins are located fairly close to the rails of the board.

Here is the board above after James has throw a shuv, you'll clearly see the location of the fins.

This picture will give a little better representation of the problem with the fin placement once the board is revert. In this picture, James is heading down the face of the wake with the board revert. Once he straightens the orientation of the board out, the nose of the board will move closer to the center of the wake and the fin that is in the left of the picture (actually the right of the board) will start to catch in the wake. Boards like the Calibrated Telum or Phase 5 Prop address this problem by providing only a single fin and moving it to the center and extreme tail of the board.

It occurred to me that as we progress the sport we are using boards in ways that some manufacturers never intended. When you ride a bicycle, the manufacturer allows some flexibility for size differentiation and riding preference, wakesurf manufacturers, don't when it comes to fin placement.

I began to toy with the idea and wondered why not allow for changes in fin placement, not only small increments, but inboard and outboard from center, as well as, nose to tail. This is a REAL rough drawing, but I going to have a board made with James' favorite outline and several fin boxes located where the vertical lines are drawn on the picture.

It seems to me that manufacturers that use wakeboard style fins could provide holes for various locations on the board such that riders could adjust fin placement to best suit their riding style. Inland Surfer does this to a limited extent on the 4skim by providing a pre-drilled location for a nose fin.

Jeff, Last year we began playing with the fin set up on my Broadcast 5.6. There are three fin positions, with the stock center fin larger than the outboard fins. We went through about every fin combination that you could on the board. With only three fin locations there weren’t too many options but we did try the following:
1) Stock three fins:…………..... Very Stable
2) Center only:…………….….. More loose than three
3) Outboard only:……………...... More loose than center
4) Small fin on center:………….. More loose than out board
5) Asymetric toe side big fin: …. Just plain goofy
6) Asymetric heel side big fin:…. Strong drive up the wake
7) No fins:………………………..…. We didn’t try this on the Broadcast

Most folks might have eventually tried 2, 3 and maybe 4 above. I bet few have tried an asymmetric fin configuration. An asymmetric fin configuration might be good for surface tricks and might be mirrored for port and starboard wakes.

Have you ever seen a hydroplane up close? Hydroplanes generally only run competitive courses in one direction, counter clockwise. There’s a huge tracking fin on the inside sponson, essentially making hydroplanes asymmetric. I don’t think you’d make an ocean going surfboard asymmetric, but maybe it’s worth looking in to for S-ing (Wakesurfing for those that aren’t up to speed with “S-Dad”).

We only played with the Asymmetric setup once, and to be honest I not sure I’m reporting the results accurately – certainly not first hand, I didn’t ride the asymmetric configuration. We set the board up this way to see if a big fin on the inboard side would help a goofy rider heel surf the regular wake. Our goofy stance surfer said that it felt like the board wanted to either climb to the lip or burry the nose in the trough.

Trick Boardz Mojo fin setups
1) Stock Fins:………………….Pretty loose, easy to start a 3
2) Reduced fins:……………….Real loose, not recommended for the first timer
3) No fins:…………………….. Like standing on butter, even “Skim That” was more stable

I have 2 "tri fins" that can be ridden in a twin, single, or tri-fin setup, (all 3 is a little tight IMO)

Hey Ed,

We tried some asy'm boards last year, Fin placement, as well as, soft or rounded rails on one side and sharp rails on the other. I even tried splitting the tail so that one side was round and the other half was a swallow. For the most part, none of the experiments were an improvement over a symmetrical board and fin placement. I think what I want to try with the new test bed is changing the fin placement in and out from the rail and also from tail towards the nose (but always both sides in unison) to see if there is a fin placement that will allow a twin fin to be ridden revert without the fin catching in the wake while also maintaining a respectable level of drive. Hopefully, I'll get better results than with the asymmetrical tests!

I've kicked around the idea of having an on the fly adjustable fin. I have something like that in my O'Brien Black Magic kneeboard. I'm not sure how you'd implement a foot kick fin, the Blank Magic fins are cumbersome to adjust by hand.

As you know I’ve built one fairly unique surfboard, I’m not sure that I’m up for another attempt until maybe next winter. I think your proposed experiment is a good approach.

Looks like Jeff is still full of inspirations.

like "I will go my way" and not necessarily wakeboard or surf way

R+D is the funnest part of the buis. Fin placement is critical and can drive you nuts. So here is a tip.
When finding the correct fin placement, I move them 1/8th " at a time, then ride it. So, when doing R+D, I use "LocBox" fin system. LocBox allows you to move the fins 1/2" up or back. At 1/8" intervals this allows me to get 16 different variations of fin placement on the same tri-fin Stix. Saves alot of time and $$$$. R+D is costly. That's why many do not take the time. If you have an idea, work it to death. Or you could end up giving up on a great plan that was just 1/8th" away from being great.

How about trying some long-based wakeboard type fins on a twin configuration. I use 1.1 A-wings on my 5'6" Landlock. They are only 1.1" tall (obviously) but they are a good 5" long. They still have a good amount of surface area to provide drive, but they are much easier to break loose as they are so short. This would also help with the fins catching in the revert issue. I would really like to see what the Walzer would do with that type of fin.

I like the lockbox idea Jerry - I should have thought of that!!!!! That's why you're the master.

Hey Nick, I need to hit you up about the Neveda INT before I forget again. Something I have found with fin surface area. Depth makes a difference. Long base fins that have the same surface area as a shorter but deeper fin, don't have the same drive. My calculations were crude, but the depth of the fin somehow provide less slippage side to side and as such, I theorize, is the reason they give better drive.

The goal or object of this experiment is to give adequate drive, as opposed to exceptional, while still allowing a shuv without catching...we'll see what happens.

"The goal or object of this experiment is to give adequate drive, as opposed to exceptional, while still allowing a shuv without catching...we'll see what happens."-Surfdad


Well than in that sense, could you get "adequate" drive off of a "wakeboard" fin?

Yes, we need to hook up on the INT. The boat show isn't until March here and I know that is when Mark starts getting the ball rolling for the season. I plan to "harass" him then.

I look at wakeboard fins as a directional stabilizer rather then a driver for skimstyle boards. Rail shape, board shape, and rocker play a large role in how much drive a skimstyle board will have without the problem of ctching in a spin. Of course fin placement is key.

OK then, how 'bout the drag coefficient of surf vs. wake fins. If you have an exceptionally fast shape, at what point do the fins "drag it down"? I don't know a whole lot about this stuff and I only have my extremely limited experience to base my opinions and theories off of. I'm new to this whole shaping thing and I'm just trying to learn, not be confrontational. I hate to even bring up the fact that I still rock the old Landlock, but it's the fastest board I've ridden or owned and the set of A-wings I put on it made it faster. Not just faster reacting and turning (although it's still a pig), but faster down the line. So it seems to me, the stock surf style fins were holding back what was a reasonably fast shape. No? Obviously the stock surfs were far from a supperior product and I'm sure there are much faster fins, but the board shape itself with the A-wings is plenty fast and now it will turn and spin 10 times better.

So back to square 1, come on Jeff, try out some wakeboard style fins on that thing. Is there any type of fin in that realm that can be used in that fin box?

Hey Nick, one of the nice things about the future's fins is that you can cut them down to any size and shape. So while a standard wakeboard fin wouldn't fit in the box, it would be easy to shape something similar from a Future's fin or probably a FCS fin.

As Mac points out - there is a LOT of interaction amongst the various design elements.

My experiment or interest is just to see if the placement of fins can be made such that drive for aerials is maintained, while allowing it to be ridden revert.

I can't even imagine the variations that would be possible with various shapes of fins.

As I mentioned earlier, the depth of the fin has a rather profound effect on the drive of the board. I don't fully understand the hydrodynamics involved, I think it must be related to the concept of a lever. The LONGER the lever the less force that is need to affect an incremental change in position at the other end of the lever, BUT at the expense of GREATER movement on the end where the force is being applied.

Maybe Ed - Big Show can shed some light on this?

Oh yeah, fin placement. Sorry if I got a bit off track. I just really like the look of the Walzer, but you knew that.

My wife keeps pushing me to make a board, so I'm trying to absorb as much knowledge as I can.

That's funny, wife wife is pushing me to NOT build another board

I have thoughts on the fin depth and drive, but its behind another surf analytical question I;m looking at, might get to it tonight.

Hey Nick, building a Poly U board is very easy. They are easy to shape and glass. The hardest part is the fin box installation. That being said, it's also very easy to build a piece of junk that was intended to be a wakesurfer. An EPS board is fairly easy to build also, but requires a bit more effort and, IMO, tools that you might not have readily available.

I'll look forward to Ed's engineering insight on the hydrodynamics of fin design.

Any tips on where to look for info on said processes?

So far as tools go, "My Dad is television repair man. He's got this ultimate set of tools." Sorry, had to.

(Message edited by nickypoo on January 24, 2007)

John Carper of JC Hawaii did a multipart video that is, IMO the ultimate for Poly U shaping and glassing instruction. They are Shaping 101 and Glassing 101 - I believe there is also an Airbrushing 101.

This is probably the best place to find shaping resources:

http://www.foamez.com/index.php?main_page=index&cPath=7_53

Thanks Jeff.

The energy for surfing comes from the wake. The wave moves at an angle offset from the direction of travel of the tow boat we call a vector.


You need to take energy from the wake vector to power your surfboard. The board has to push into the wake and split the vector in to a forward component and a component driving across the wake.


The harder you can drive or push across wise the faster forward you should be propelled. You push the fin against the water, against the wake vector. A larger fin has more water to push against and can provide a larger forward vector.


I think this is very similar to how sail boats work. Fast sail boats have a large fin, a keel. Wind pushes against the sails and mast, the keel pushes back against the water. If you reduce the area of the keel then you can’t let the wind push as hard and the sail boat won’t go as fast.

I do agree with that concept Ed. However, I probably was unclear in my experience, it's more than just area. So as Nick suggests a long base with shallow depth should provide the same "drive" as a short base but deep depth fin with the same surface area. In my experience, the short base, deep depth fin provides more drive.

I started writing something on depth but I thought I was getting long winded. The density of water varies little with depth, but the pressure increases dramatically. The pressure at the surface is one atmosphere, 14.7 psi.

Right at the surface if you push the water to the side it’s easy for the water to go up into low pressure air. Pushing water from 4 inches deep is different; you have four inches of water above the fin that you’d have to move first.

Some Olympic divers dive deep from the starting block and porpoise at the bottom of the pool on their first breath. Why, because you’re pushing against water that’s deeper, has more pressure, and provides more to push against.

That’s my intuitive analysis on depth.

One thing I’d also add though is that my Trick Boardz Mojo has a deep concave shape. The long board edge gives the board a lot of drive, it’s the fastest down the line board I’ve ridden. Its pretty easy to drive a long section of the edge deep in to the wake, giving a lot of drive.

one thing, we are riding not only in pure water but also on a mixture of water a air and on some foam too and its different enviroment than pure water

Interesting that the consistency of the water at the surface is significantly different than three inches deep, but that makes sense, especially when you consider the air/water mix like Petr points out.

Again, my experiement is dealing strictly with fin placement, not the shape of the fin or as Ed and Mac point out the shape of the board itself.

I'm not sure if it's that the Mojo doesn't release water well or what, but we want the drive so that the board will be able to do aerials, then also be able to ridden revert. How are your shuv's and airs coming along Ed? You don't often see pictures of folks with the Mojo in the air.

The Mojo XL is a BIG board. At 210 to 220 pounds the Mojo XL is much bigger than I need. I did ride the next smaller board at the Morse Lake Gathering last year. The next size down is really the correct size for me, it's much more responsive.

I can spin both the Mojo XL and the Grande very easily but I haven't attempted airs or no shuv-its on either one.

Ok maybe a thruster fin, and not dolphin shaped- around 2 inch. deep with lots of foil for max lift. Mounted with just enough clearance not to interfere with catching while riding switch. Lift =power and drive.

The fins on this Walzer are in the 2 3/8 inch depth. To equate to the same surface area, would require a single 5+ inch fin. I think that stepping down to a single 2 inch fin would result in a significant loss of drive.

I also don't like the reduction in "looseness" of the tail when riding with a single fin. Maybe moving it forward towards the middle of the board, much like the 4skim, is the answer.

I want the board to easily break loose also. I want it all!!!!!!!!

This is fantastic. As soon as I saw the pic I got it. Nice explanation though Mr. Bigshow. I was poking around looking at fins a bit yesterday and I was looking at the Lokbox Bonzer set. They were the closest shape I could find to what I was looking for. Definitely not what I was looking for, but as close as they had. Two sizes to work with and adjustability. Hmmmm. It just seems to me that that shape of the fins on the Walzer don't really lend themselves to riding revert. The shapes I did find that I was looking for were either kiteboard or wakeboard fins, which poses another question. How different are the actual foil shapes between surf fins and wake fins? If there is any difference, can a wake fin shape be combined with a surf fin foil? Do I talk too much?

The shape of the fin, when revert (as opposed to switch which I believe refers to the relationship of the rider's stance in relation to the direction of travel) has little to do with hanging up in the wake. Even if shaped to cut through the water, the fin that is closest to the wake if it CATCHES causes the board to pivot around that fin. It will obviously have more drag than the fin that is still in the air. Also, since the fin is off-center, and has a toe-in the drag pulls the board in that direction.

As Mac points out a thruster or the center fin for s-boards has a full foil that is similar in design to wakeboard fins. The side bites for s-boards typically only have an outside foil.

We all talk too much, it's best to not question the dysfunction, accept it and move on.

To achieve it all takes knowledge trail and error and luck. Some things just work and some things don't. Thats why this thread is so interesting. People are testing and comparing new products and ideas that are setting standards and trends in the industry. Thats why Independent Board Reviewer goes to Jeff W. so that us G.P.S's
"General Public Surfers" have a clue. Thanks Jeff.

I used to listen to General Public. Hell, I even saw them (sort of them) in concert a couple of years ago. Saw the same "sort of them" as the English Beat last year. I bought a hat.

Man, I'm ready to buy me a new Walzer, but my E-mail is on the fritz and I can't send, only receive. Anybody have a good 'ol fashioned phone number?

Nick - you've got mail!

Thanks stu!

just in case you dont know how it works under

http://img.timeinc.net/surf/content/images/07/wallpaper221/andy.jpg