I am trying to further my understanding of fins and how they work. Can anyone explain the function of all parts of the the fins? It had been described to me that in a thruster set up, the center fin was for your bottom turn and the rail fins helped you come off the top. I don’t really buy that simplicity anymore. I have also heard the base of the fin is for drive, is that true?
Also, what is the function of the rake on a surfboard fin? Many fins used in other applications by humans have no rake, i.e. sailboat skegs and airplane tail wings. Just a curiosity. I’ve done some experimenting on my own but I find with the varying conditions its hard to do a proper ride report, and frankly all the experiments have worked, so I can’t throw out any failures and tweak the designs intelligently.
Finally, I was piddling throughot the archives looking for a post by I think Jimthegenus,or maybe chippy where he lists how many layers of 6oz to make fins to fit futures, fcs, and single box. Couldn’t find it, anyone know that info off hand?
I'm surprised you ever did. It's overly simplistic and isn't true.
Multi-fin set ups in particular are fairly complicated. Look at most any surfing photo and you will see that for the most part all of the fins are engaged to some extent.
The base length is related to drive but isn't the end of the story. The overall rake... from base leading edge to tip (measured fore and aft) is related as well. So is the fore/aft spread of the fin lay out.
Don't discount fin thickness and foil. A thinner fin is more likely to maintain direction vs a thicker fin. The outer surface of the outside fins will play a big role in rail to rail transitions. It has to push sideways through the water while the inside surface of the inside fin 'grabs' the water.
Fin flex?
Toe-in and cant?
For a single box fin about 36 layers of 6 oz cloth should do the trick. If it's too loose, add a couple layers on the tab. If too tight, break out some sandpaper.
Considering the size of most fins, it is truly amazing what they do. George Greenough said somewhere that pros should devote something like 40,000 - 50,000 dollars on fin R&D alone. Phil Edwards told me that the fin is one of the most important aspects of board design. He said, "Don't believe it? Try riding your board without a fin."
I agree the aforementioned quote from Phil Edwards,
if I wanna change the feel of any board, I just change the fin setup.
So many things have been tried over the years and left behind for some reason or another, but with the changes in boards recently I wonder if some or all don’t deserve another look…but how to narrow it down?!