Marc, here’s a good thread to go down the rabbit hole of thick vs. thin fins:
jspr, that’s a great trick with the feather boards. Might be able to use my friends router table at his shop to try that out.
My son broke the tabs off one of his FCS twin-tab fins, so was trying to figure out the best way to make a replacement. Gonna have to try that router trick. That video also gave me the idea of just molding the whole solid base in place then just remove the unwanted material. I’ve always tried mold the tabs in their final shape which is finicky and hard to get to final shape without oversanding or making them too weak.
Would love to see your molds too.
Just cut/foiled a fin last night after seeing the router trick to try that out and see how it goes, so thanks for the inspiration!
Yep, I read it back in the day (another username) and that’s where I came up with this opinion; it’s definitely not mine. I love Thrailkill and have even talked with him on the phone. He’s a big proponent for alternative fin setups and thicknesses. I owe a lot of mind expanding revelations to him. I was just throwing it out there for future minds to ponder and/or start a discussion with likeminded individuals.
It’d be worth starting a new thread. There’s a lot to learn there, and it may inspire a new crop to do their own experimenting.
I got my own thoughts/hot-takes on fin thickness/outline and have made a few fins of varying thicknesses to test out theories. They all seem to work reasonably well, surfing is so subjective though, performance is a really hard metric to quantify.
The simplest variable to play with is fin surface area (SA). There may be an optimum fin SA to rider weight (W) relationship (SA:W). When you find a fin planshape and foil profile you like, you scale fin surface area to match rider weight. Easy enough to test.
This is how the moulds look like… obviously not as clean as the ones in the video, but up to now they work surprisingly well. Unfortunately I have no fins at home at the moment , the white one is the 3d printed " positiv" that I used to make the mould.
I’m going to make a set in the next days , I’ll make some pictures of the process and post it.
I wish I could contribute something solid in terms of fin theory , but the opposite is the case . I don’t know anything…
I was inspired by a couple of cool threads here on swaylocks, including one about thicker fins-and Hans finfoil App.
It’s cool to read through this older discussions and see how little I understand about this magic fin things.
Oh wow, that’s a really good setup! Well done. I’d love to see pictures of the process. I’ll most likely never make fins in this way as I like to experiment with different designs so generally use the panel method, but I love seeing the process. It’s always interesting, thanks for sharing pictures.
Hey Marc and lawless,
I’ve been crossreading through this and other older threads for a while now, and I feel I need some help to navigate me through.
I’m sold now on doing thicker single fins for a couple of reasons,
what I completely fail to get is the side fins.
Starring at the fins I have I see only asymmetric side fins , the majority has an inside foil , the only exception being a takayama twin fin by Larry Allison which is flat on the inside.
They all are pretty thin , I’d say by a rule of thumb their maximum thickness equals the tab thickness of 1/4 ".
So that would be suspicious that the manufacturer uses as little material as possible to get a fin out of something fitting in the existing boxes, but then some of them are injection molded , or made with an 8mm sheet ( 4wfs) and then cut down to be thinner.
jspr, another thread for you on thick single fins:
“Is this mainly to keep the drag low?”
Not sure why ~1/4" seems to be the defacto thickness for most fins (in context of shortboards).
Hot-take on why it’s that way for injection-molded fins, there’s a point where injection molding has a max wall thickness before you get “sink marks”. My guess is this was a limiting factor?
And they seem to work just fine, there’s so much variability in surfing, even if you could quantify a 15-20% improvement in drag, in the real world that probably isn’t noticeable.
I think of the aerodynamics of a flat plate vs. an airfoil. It’s very counter-intuitive that a flat plate has significantly more drag than an airfoil that is multiple times thicker.
Mostly it just matters to us on the fringe who like to tinker around with this stuff.
In my mind the benefits would seem even greater for a single fin longboard though. There are a lots of threads buried in the archives of people making thick fins.
Also, what stoneburner said plays into it… in theory a thicker foiled fin should generate a bit more lift so you could reduce the surface area (ie: reduce the overall template size).
Thanks!
Really appreciate the input!
Started to reply yesterday , but couldn’t finish , and later found that my thoughts had gone in circles.
Like you said , there seems to be a consensus that side fins work well just the way they are , I’ll make thicker ones and see what happens.
Does anybody know what happend to Blakstahs system? I couldn’t find any trace of the surf trucks…
What’s your take on clustered fins?
Bill Thrailkills twingle setup seems to incorporate a radically different idea - stabilizing a protected low pressure zone between two fins - ( which in my mind offsets the idea of the importance of area of fin in the water ) .
Am I just tripping here with my understanding of the setup?
My only metaphor for understanding this has nothing to do with surfing. What I feel in the pool when swimming laps together with good and/ or bad swimmers , or what happens when drafting on a bike in a group translates more into my concept than surfing.
I should stop reading psychedelic fin threads at night…
@Railwaysurfer
Making the moulds is actually a spin of of trying to print fins in a variety of sizes and foils.
I couldn’t get to work what others showed here on sways, printing the core and then glass over.
If I print the fin to it’s exact size I end up having the same trouble like lawless , it’s difficult to get the dimensions for the box right without compromising the strength of the glass.
The moulds are a bit of a dead end though, it’s time consuming to make them , but they allow to play with the layup of fibers which is cool.
The next thing I will try is to print the fins with a slot and insert a base of g10 . I have yet to find out which material prints best and glues best. Comes in handy to have a fat foil;)
You could spend your whole life messing with fins. And if you do, post the results.
The twingle setup allows for a smaller set of fins. How much is up to experimentation. The twingle setup is heavy with traditional boxes/fins, so smaller fin size is good.
You can build fins and postulate up to a point. The best test will be in the water.
Ooh that’s got the wheels turning!!! You could get a base machined out of light weight aluminium and use a machine screw to fix different fin templates over the base. You could do the same with solid fibreglass I guess?!
What would stop you glassing a solid base onto a board and having a “cover” fin slip over the base? You’d have the advantage of glassed on security with the interchangeable aspect of boxes?
The old Morey-Doyle closed-cell foam boards had an embedded FG tab that rose out of the board. The fin slipped over the tab and was held in place with 2, 2-piece screws.
Hey Stoneburner , thanks for helping out!
Took some time to read through.
I’m not sure if I understand the below regarding the distance between the fins:
“this shows indeed that fins close to each other should have roughly the same size as the single fin. While a twin fin on the rails can reduce the fin size to almost half the size.”
Below the quote from the OG post…
Oh interesting, just goes to show that just about everything has been trialed by someone, somewhere at some point!!! I wonder why it never took off, seems like a good system? Manufacturing ease maybe a reason the current system took precedent?
I need to read the Twingle thread, still going on the Thick vs Thin!!!
I’ve trialed the Duo set up and really like it, just a case of bringing them in a bit closer!
I feel the same. I asked him , to understand his answer more homework on my side is required;)
My problem is that Im not sure if I understand the vocabulary in the first place.
I’m a retired scientist. While I have some decent understanding of the most basic concepts, for me, fluid mechanics gets very abstract fast.
Here is some more of Hans’ input about the Thrailkill Twingle.
