If you are making the pivot fin a cutaway, is that because the base is a bigger part of the equation than the tip of the fin for toe-in?
Is this just another optimized fixed fin design? (All the current available variable fin designs seem to work fairly well)
How is this copying nature in any other manner than just the outline and foil?
Has anyone used another modified man made wing design - the propellor – to make fins? You know, with the base of a fin parallel to the stringer and the tip toed-out (in?) or made the base of a fin toed-in but the tip parallel to the stringer? Sorry about this one…
And can’t you put a knife cutter on the leading edge of that sailboat keel to slice the kelp as you move through it instead of backing up? (probably something in the rule book?)
…Hmmmmm - I’m probably just rambling on most of these. But has anyone tried the variable rate of toe-in thingie?
It took me two days to rearrange the letters in HalSose’s name for Roys favorite word! And then only because I was in my car yelling an obscenity at a driver in front of me…LOL
Then how about a really strong (foiled) wire from the bow to the tip of the leading edge of the keel?
Kinda cool, you should make on out of 34 layers of 6oz glass and lam resin.
But foiling to avoid spinout at planing speeds would be a daunting task indeed, as anything tapering from one sided to double side foils would be hard to keep quiet.
Base HAS to be much thicker than tips, or they delam/snap off on any strong turns.
Hey, how’s about Blakstah’s rotating single fin box?
I knew I should have posted on “Banzaii’s Samurai Swordmaker forum” They never give me flak for making my foils to thin!!! Should be steel - ala Mr. Greenough? How come my design (idea) will take so much more stress than those flimsy fcs molded plastic directional whatevers? Is my head swelling? - wells I’m gonna pop…must have more feedback. I thought (heard) that the fin sings from an improperly done fillet?
If you are making the pivot fin a cutaway, is that because the base is a bigger part of the equation than the tip of the fin for toe-in?
I’m not sure I get you. What is the pivot fin? Thrusters have rail fins and a trailing fin. If you mean rail fins…I think cutaways are just good design. The water near the board is being dragged along with the board, so the velocity difference between the water and fin is less. Further from the board, the velocity difference is greater. Drag, and drive, depend on the difference in velocity between fin and water. Honestly, I think every fin is better with a shorter base than the chord length 2 inches up. Chord length is the length of the fin parallel to the bottom of the board. The cutaway lets you use longer chord lengths when the difference in velocity is greater. Of course, reducing induced drag means the chord length has to be small at the tip.
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Is this just another optimized fixed fin design? (All the current available variable fin designs seem to work fairly well)
How is this copying nature in any other manner than just the outline and foil?
Actually, if you are referring to Bert’s fins, it is unclear whether/if he has relied or used inspiration from nature for the foil. Some others do. I don’t think it is appropriate to “copy” nature, there isn’t a close replicate of a surfer in nature. However, figuring out how marine animals use fins to re-direct themselves, and testing aspects of their design in our boards may be a pursuit that improves function.
If you wanted to foil like a dolphin fin, you might consider the max thickness of a dolphin pectoral fin, and its wide point.
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Has anyone used another modified man made wing design - the propellor – to make fins? You know, with the base of a fin parallel to the stringer and the tip toed-out (in?) or made the base of a fin toed-in but the tip parallel to the stringer? Sorry about this one…
Yes. The water near the base flows to the side and to the rear relative to the board. The deeper water flows in a different direction. Some make their fins to account for this, with more toe-in at the base than at the tip. This lets the entire fin apply a consistent AOA to the water.
If you are making the pivot fin a cutaway, is that because the base is a bigger part of the equation than the tip of the fin for toe-in?
It’s because we theorize that there is more drag occurring at the fin base due to laminar flow and up wash interaction. Consequently a shorter fin root cord length is used to minimize the area of interaction.
Is this just another optimized fixed fin design? (All the current available variable fin designs seem to work fairly well) Yes, but Blakestah is also tweaking camber by narrowing the AOA he expects the fin to experience through pivotting the entire fin.
How is this copying nature in any other manner than just the outline and foil? You gotta get ideas from somewhere.
Has anyone used another modified man made wing design - the propellor – to make fins? You know, with the base of a fin parallel to the stringer and the tip toed-out (in?) or made the base of a fin toed-in but the tip parallel to the stringer? Sorry about this one… A propellor is twisted that way to make up for two things. The tip of the propellor is traveling much faster than the base so less camber is required at the tip and it has something to do with down as well.
And can’t you put a knife cutter on the leading edge of that sailboat keel to slice the kelp as you move through it instead of backing up? (probably something in the rule book?)
Yes, you can and many boats do have a kelp cutter. The only problem is the boat I raced on last weekend didn’t. I told the owner I knew a way to retro fit one. But, it would be expensive and change the cord length of the keel. Which is a no-no in one design.
…Hmmmmm - I’m probably just rambling on most of these. But has anyone tried the variable rate of toe-in thingie? Naw, we’re all just bouncing ideas off each other
OK - round two. I’m kinda rested up - feel pretty good, so…
Thanks for the answers, first of all.
My level of understanding shot way up when you were answering direct questions (must remember - direct questions - not what ifs?)
So what if? - jk
I’d like to respond to the pivot fin misunderstanding. When Simon Andersen invented the thruster he was competing with Mark Richards at the time who was whipping his — with his twinnie. I thought the fins on the twin were referred to as “pivot” fins? Anyway we all saw the movie Freeride where Mark Richards was doing his act at Off The Wall and then out of the shadows came Shaun Tomson and we were all saying in our heads if only we could put those two board designs together… which is what Simon did. So my question to you Blakestah is; when you look at a thruster do you see a single fin with the center fin pushed back and two side fins, or do you see a twin fin with a stabilizer or trailer fin?
A simple test will answer this. Take off your inside pivot fin. now go and surf - Yow! Put it back in and take off the back fin and surf. Which set-up works?
The real fruit of the shortboard revolution happened a long time ago in Newport with a twin fin fish “black ball beater” but it just so happened that the man who pulled it off was extremely humble and to this day hasn’t complained about the way the cards were dealt.
The Steve Lis fish was a kneeboard with keel fins - the David Nuuihwa fish (the smaller one, not his “longboard” fish) was a stand-up surfboard design.
Is there an optimal placement of the cluster? Or is it “outline” dependent?
if i had to make a call on where to put em on that board …
id say 12 and 4 is a safe place to start …
from there you can fine tune for future boards…
blakestahs cant and toe were pretty much there…
i see a thruster as a twinny with a tail fin…
but either way, which ever fin you make bigger the board will start to feel more like a twinny or a single depending on the size of your sides or tail…the biggest fin dominates the feeling…
look at where singles traditionally dominated and where twins dominated ,
and we see the reason why thrusters lean a little to the single for some waves and a little to the twinny for others…
