Advanced Fin theorys

General Discussion
1

Okay, so this article I read a long time ago about fin layup and how important it is, including the foil makes the board. So I read the last issue of TSJ, and they have a number of interviews concerning this exact subject.

First off, fin flex. The way you lay up your ply’s of glass or carbon or whatever - whether its 90degrees or 45degrees, maybe a 70/30 all makes the fin flex and perform differently. Does anyone have experience with this? Maybe give some advice on exactally how to lay up with this process and how it works. (?) please.

Also… on the same subject of fins flexing… either at the tip (where you want it) or the base (non glass on fins), comes the question of the integrity of fin boxes out there. From what I’ve gathered, FCS are possibly the worst as far as flex. But its hard to find any information regarding the integrity of fin boxes on the maket. I use ProBoxHawaii fin boxes, myself. Anyone have credible arguments Vs. fin box systems?

Cheers

2

Tomatdaum has some very futuristic fins in the works.I have a set and they go really good !

a GREAT combo for glassons are veener ply inners and high density foam outer…to this date,for me it’s a hard combo to beat !

3

I am interested in Pro-Box–they have some kind of insert the fins are seated in? Do the inserts add flex as far as you can tell?

Also do you know what time the next train is supposed to arrive at this station?

4

The inserts allow you to adjust the cant of the fins. Works really well, not any flex as far as I can tell. But i’m sure there is

5

Fiberglass cloth or any woven fillament cloth have the fibers oriented in primarily two directions. The warp direction is the direction it has the most tensile strength in and the fill direction is the direction with the least. If a cloth is woven such that most of the fibers are in the warp direction, then this cloth is refered to as uni-directional. Weight to strength ratio is optimize in one direction and that direction is the direction of the warp. If the cloth is woven such that the fiber allignment is 50/50 between the warp and the fill directions then it is refered to as biaxial cloth. Most clothes that are used in mainstream surfboard production (S & E clothes) are biaxial. They lay down around contours better and work sufficiently well enough without intricate fiberorientation or path load orientation. But, if you need to reinforce a laminated structure their are engineering programs that specialize in load path fiberorientation.

Now back to surfboard fins. Since most of the materials that the industry is used to working with are S or E clothes in either an epoxy PE resin, this is also the most common method for making fin panel laminates. Again these are biaxial clothes with their warp at 90 degrees to their fill and the fiber orientation is a 50/50 split. So, if you layup say 16 layers of 4 ounce E cloth in a flat panel with all the warp and fill alligned the same that flat panel will resist flexing the most in the the directions of the warp and fill and flex the most in the direction 45 degrees to the warp or fill direction. Now if you stagger your orientation at 90 and 45 degrees you don’t give up as much in the primary warp and fill direction as you gain in flex resistance in the 45 degree off direction. Now this is all in a flat panel. When you shape a laminated fin you taper the laminated panel into the foil shape and taper in from base to tip. So, much of your flex resistance comes from whats left after you’ve foiled your fin. Since the base and and area 25-35% back from the leading edge are the thickest and consequently retain the most laminates of the matrix you originally layed up in the flat panel, the fin resists flex the most there and flexes the most out at the trailing edge tip where the most has been removed. Now that tip is around 35 degrees from the most flex resistant portion of the fin. So, if you want to stiffen the tip for any given lamination schedule it’s not a bad idea to orient at least a portion of the warp in that direction.

Now, do we really need to get into attachment methods. I’m sure you can find all kinds of arguements in the archives. But, I’m partial to Red X, LokBox and 4-Way due to tapered fit, load path orientation, adjustability and the fact that I make them.

6
Quote:

But, I’m partial to Red X, LokBox and 4-Way due to tapered fit, load path orientation, adjustability and the fact that I make them.

Atleast your honest about it :wink:

regards,

Håvard

7

Okay. Thanks for the info. I havn’t made too many fin panels, and dont think I’m very consistent yet. How many layers of what ounce cloth is a standard for laying up the panels? Whats a target thickness of a panel?

8

Now you’re getting into foil design. You want to have enough thickness to get all the curvature you want out of you foil design. But, most people layup panels between 1/4" to 3/8" thick. Depending upon what ounce cloth and how well you squeeze the excess resin from the layup with determine how strong, flex resistant, heavy and how many layers you’ll need.

9
Quote:
Okay. Thanks for the info. I havn't made too many fin panels, and dont think I'm very consistent yet. How many layers of what ounce cloth is a standard for laying up the panels? Whats a target thickness of a panel?

The archives are there, search them…tons of info there.

For thruster fins at least 0.25" thick, for singles at least 0.375" thick, 6 oz E cloth is roughly 0.01 inches thick per layer if you roll a good panel.

10

…comes the question of the integrity of fin boxes out there. From what I’ve gathered, FCS are possibly the worst as far as flex.

Not sure what you mean by flex. Flex where? When properly installed, flex in the FCS plug/insert is practically zero. If the fin fits loosely in the insert, you’ll get lots of movement. Fin material is also a major factor.

But its hard to find any information regarding the integrity of fin boxes on the maket.

‘Integrity’ meaning what? Reliability…total failure…flexibility?

Ive used/installed FCS, Lokbox, Futures. Each have their pros and cons.

I really like the copious FCS fin product line, and Im all about choices. Install is a breeze.

I really like Lokbox’s versatility and strength, just bought four boxes for a Quad Im currently building. Fin market availability is not strong.

I like Futures the least, mostly cuz my board’s core’s are very light…theyre fine for poly. Their stock fins are stiffer than the stock FCS and seem to have better foils.

RedX sys is a very robust design and allows adjustability.

I love all the system choices we have. It makes installing and tweaking fin setups much easier for the backyarder and pro builders. Say what you want about FCS, but if it wasnt for them we all might be still riding glass-ons (fine if youre set on one setup ALL the time) and Bahne boxes. They started the whole thing. Kudos for their competition elevating fin tech and pushing all the others to do the same. Textbook free market competition at its finest.

11

I had a discussion once with an aerospace engineer about fiber alignment. He talked about many of the things you have here, Tom, but also mentioned that heat/cold can cause the different layers of the lamination to expand/shrink (or want to expand/shrink) in different directions when the layers are oriented differently. He said that this is something that is considered in air foil design when building a variable pitch foil. For fins though I would think that you mainly want to be extra careful to keep these types of fins from baking in your car since twist-type deformations may be somewhat more likely.

12

StinkBug,

      We just submitted a bid on a mold for components on a sensor housing designed by a big aerospace firm. The anticipated operating temperature range for the parts was -30C to 100C. I think the operating temperature range for surfboards is a bit smaller. I agree it can be a factor, but only in the absolute extreme.
13

You only have to worry about the fibers deforming depending on how everything kicks off. If its air cure, it could make a difference, but not enough to warp from sitting in a car. Aerospace parts are all cooked out in an autoclave, completely different. I actually manufacture aerospace parts with prepreg for a living.

I could be wrong about the temp change, but depending on the material and resin, normal wear and tear everything should be fine.

14

What do you guys think about carbon for fins? I was thinking it would be cool to have a couple of carbon layers right in the middle, so that it doesn’t hurt the shaping of the fin too much (I’ve heard that carbon sanding is a pain), but still gives strength.

By the way, what aerospace companies do you two work for? (Originalsin and Tomatdaum)

15

I’m not sure carbon center would be the most efficient for JUST adding strength.

If you ever get the chance with some scraps… try this for an experiment…

Take 3 pieces of regular cloth, wet, spread it out… let it kick. Now see how flexible it is, and do some of your own durability tests, whatever you want.

Next…

Take only 2 panels of glass, and in between add a piece of chopped matt. then glass that. Do the same durability tests.

You’ll see how amazing it is.

Furthermore, as far as adding a different material to the center for strength… you can always add a piece of honeycomb core. But that is a different animal all together.

16
Quote:

Take only 2 panels of glass, and in between add a piece of chopped matt.

Interesting Sin, what weight of chopped matt? (ounces/ft or ounces/yd) Isnt chopped matt much thicker than equivalent weight woven glass? (most of the stuff I can get is in the 13 to 18 oz/yd range) When comparing the two test panels, are they the same overall thickness? Thx

17
Quote:
What do you guys think about carbon for fins? I was thinking it would be cool to have a couple of carbon layers right in the middle, so that it doesn't hurt the shaping of the fin too much (I've heard that carbon sanding is a pain), but still gives strength.

By the way, what aerospace companies do you two work for? (Originalsin and Tomatdaum)

Fin stiffness and strength are contributed most by the outside layers.

Layers of carbon in the middle do very little for bending stiffness.

You also need to be sure to use a high modulus epoxy for your resin, if you use something as stiff as a normal laminating resin the carbon will hardly change strength/stiffness at all.

A good way to do it is to make a glass fin just a TINY bit thinner than usual. Then lam 1 layer of 6 oz carbon on the outside of the fin, using a high modulus epoxy.

The problem with foiling carbon is not so much the resistance to foiling…but if you put carbon next to glass the glass layers will grind much faster than the carbon, so it is tough to have a smooth finish.

18

I wouldnt go out and buy material to do that experiment, just use scrap. However, the chopped layer will be a bit thinner that the glass your using, depending on if its 4oz or 6oz. But just by adding a layer of that chopped the overall strength is incredible.

19

Concerning carbon fins, there is so many types of carbon that I’m not sure what would work best.

Also, I’m not sure about the ratio if you were to use fiberglass plys in the center and wrap them in carbon. I think I’d try making a set out of carbon/carbon first, and use a high modulus epoxy like you were talking about.

20

Here are a few notes I’ve taken regarding this… maybe it’ll spark some content.

Carbon Material:

-about 20 diff types

-t300 most common

Fin Boxes:

-how the fin is attatched to the board is key (there are pro surfers who dont endorse fin boxes because of performance reasons)

-dont want flex at the base

Foils:

-foiled fins produce power

-a single fin with a symetrical foil going dead aheat at zero degrees angle of attack, its not producing power - its just cleaving water

-as soon as you put the fin on an angle you start to produce power on the side your angling toward. - so the inside of the fin starts to suck itself

into the wave and water rushes past the other side which provides hold. Extrapolate that principle out to all manuevers all turns and your producing

power all of the time

-most of the power of the fin comes from the bottom half - finisse comes from the tips: control, adjustment, launch, spring, spill

Flex:

-softer(bendy) fins help board feel loose, but not a lot of return

-soft fins also cause wash outs, slip and throw off trimming.

-slows reaction time out of turns

Wood fins:

-float (should not add material that doesnt float)

-good flex

-can lay up and control grain orientations

-alter flex by foiling certain ways

-strong, stubborn

-memory.

Okay… these are just a few notes that I found relative. One thing I didnt mention is the use of concaves on the inside of fins. Also very interesting I was hoping to get some meat and potatos conversation on this thread about the important and often overlooked attributes concerning fins.

Hope someone has found something useful…