Singlefin, TwinFin, Tri-fin which is the driviest?

General Discussion
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I rode the board at Oceanside, then again a couple months later in Ventura. Both times waves were a couple feet over-head with some workable face, and not too much texture. I’m not sure how the board works in other conditions.

The fins were in were specially made Hydro Epic 9’1" longboards - carbon / Kevlar / aluminum honeycomb / hollow - the boards weighed about 10 lbs, and were heavily reinforced in the tail section (after about an hour, I ripped the fins out of the first board - the Futures guys said I would, I didn’t believe them, then it happened). The center fin was moved forward a bit from normal (I don’t remember exactly how much, although I think the side fins were responsible for about 95% of the boards performance, and the tail just kept things stable). The side fins were forward from normal placement by a couple inches, with much less toe-in (almost straight). They were also moved inward a bit - mostly to keep the tips of the fins from sticking out the side where they could slice you to bits in the wrong kind of fall.

The extra speed was there because the drag of the board was greatly reduced. The Futures guys said the board design wasn’t so much of a factor since the fins do so much of the work. Again, I didn’t believe them at first, but after the first wave my opinion changed dramatically.

Even though the board looks like it’s in the water like normal, it didn’t feel like it. I’ve ridden many (I mean many) Hydro Epic longboards (I was one of the founding members) and this wasn’t anything like the others. The fins lift the board up out of the water and nearly everything happens from the tail - this is the paddle-in version of Laird’s hydrofoil. The boards want to climb the face of the wave at all times. Instead of cranking bottom turns to get up the face to generate speed, I found myself looking for ways to slow down so I wouldn’t leave the waves in the dust.

There is ZERO side-slip when turning. It felt like I was on rails. Turns generate even more speed, since no energy is lost out the side. Another thing I noticed is I could stand on the nose and the tail would stay in the water - something I coudn’t do on the other Hydro Epics (remember they only weigh 10 lbs for a 9’1"). One thing I couldn’t do is swishy turns off the tail like I often do to scrub speed.

This setup opened my mind to what can be done with fins, and made me believe the guys at Futures know more than I do about hydrodynamics. Other than having the best box system, they also make the best fins. Try their Vectors on your normal board - same general size and location - if you don’t feel the difference I’ll eat my hat (even though I don’t wear a hat).

These fins are the polar opposite to Blakestah’s rotating fin systems. I tried those at OB in San Francisco. They made me feel like I was riding on a “lazy susan”. Both can be fun, but they are comming from totally different worlds.

42

I just re-read the very first post, and it’s a pretty good statement–seems like your drive comes from area added to rail fins, and your stability comes from area added to center fins.

It makes me wonder though about quads, and seriously, Griffin’s 5 finners begin to make a lot of sense. Less drag from a smaller center fin, and all the drive of the center + whichever rail fin is engaged. YOu have to wonder if quads have reached anything like their full fruition. I think about a fairly full-sized fin behind each rail fin, the rail fins moved in a bit, the trailers inline behind each…

Seems like that multi vortex generator design got the templates reversed for rail and center fins to me, but that’s me

43

Here’s my take on the subject. Lets first eliminate as many variables as we can. Given 3 identically shaped boards, a single fin, a twin fin, and a tri fin, all with fins of the same shape, but equal in fin area for each board, I believe the tri fin will be the driviest.

Here’s why. During a bottom turn, the single fin would have the most fin area in the water at 100%. The twin fin would have 50%, and the tri would have 66%. It might seem logical to say the single fin has more drive because it has the most fin area in the water, but I think there is more to it than that. On the tri fin the fins are spread apart which gives more drive than the single fin. I’m not sure of the physics on why there is more drive, but this can be evidenced by moving the fins on your tri fin further apart nose to tail. I’m sure everyone will agree that front fins further away from the back fin creates more drive than closer together. This can’t be done on a single or twin fin. A quad would have less drive than a tri fin but more than a twin fin, given the same spacing as the tri fin, because only 50% fin area is in the water.

I know it’s not part of the topic, but rails have a lot more to do with drive than fins. Thin rails are like a long fin and can contribute a lot to drive but they still need a fin or two to control it.

44

drive meaning?

is it just positive response from burying the rail ?

ie. you can feel the power of the wave more

rather than just skating over the top.

yes i have to agree that rail fin area is the largest contributing factor

in a thruster

and why twinnies with larger templates generate this drive feeling

i guess there a few types of drive as well

rail drive on a thruster and drive from a flexible single fin

i think that for me fins and fin position are the most confusing yet critical element in gettin speed from

a surfboard

when you see a surfer talking concaves and outlines wrt performance, yet the only templates hes ever surfed is the fcs and 11

well you gotta wonder???

although its a nice fast setup

i personally think at 85kg that this setup lacks drive and has a very narrow sweetspot.

my favourite board has a k fin template thats scaled up about a centimeter all round with a thicker foil

and it made a huge difference giving the board a much more positve drive feeling

and no babying through turns on bigger waves

mvg reduces drag on the trailing fin and allows it to work @ higher AOA

Herbs superchargers work in similar way im told for twinnies etc

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Quote:

Ah yes,

The famous ancestors, the Neanderthals. I think you are right up there with the best of them. It’s not hate Roy, it’s intolorance of the level of misinformation that you regularly promote. It’s insulting to anyone with the slightest grasp of how surfboards and fins function.

Quote:

That’s an outrageous thing to say. . . . calling me Neanderthal is a personal insult, please stop saying insulting and hurtful things, it’s a stoke killer… . . you make personal insults against me in nearly all of your replies. . . it’s just not nice. Regarding the tunnel fins, you have offered no hydrodynamic reasons for your anti tunnel fin stance, and yet you blithely say that I am offering an ‘insulting’ level of misinformation. . . . this is unfair. . . . the tunnels provide lift and drive with low drag, that’s all. . . . it’s not misinformation.

 <span style="font-weight:bold"> Be a gentleman Roy, and don't keep the antagonism boiling. We can agree to disagree, and let it drop.</span>

Bill, I have no antagonism towards you. . . if you go back through this thread you will see that you have repeatedly insulted my intelligence and my character . . . . this is against the rules of Swaylock’s, and to be honest, I don’t like it.

All I wanted to do was put my 5 cents worth in. . . . you don’t have to respond if you would rather discuss tri fin and twinfins.

46

Hey Tom, Glad you’re trying stuff and good to hear opinions on everything.

Bill, you have always seemed informative and diplomatic. Perhaps you have caught that computer virus called ‘forumitis’, and some have caught a mutation called ‘firewireitis’. Lots of people here and on other forums seem to have it. Walk away.

Back on subject, the most drive I’ve experienced have been with in-line fins, a single fin derivative. By drive I interpret as hold, power, projection and acceleration. My new project is in process at the moment so will post pics eventually.

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It’s later now… pics now pics now pics now

sorry–I developed one of them syndromes too

Inline fins are Very interesting!!

48

Janklow, you’ve got the same virus as Chipfish!

Be patient and the symptoms may go away, or not.