What does decreasing the size of side fins do on a thruster?

General Discussion
21

Just a data point about tiny sidebites…

I recently ordered some of those little Lexan “TurboThrusters” to go with the 7.5 “TurboTunnel” that I’m using on my 9’1" Driftwood.

I was amazed at how small they were when they came in the mail, maybe 2.5" tall at best, and very flexible. I was skeptical that they would have much effect.

But I tried them anyway and they have made a very noticeable difference vs. the single. Sharper turns and a little bit more ability to pump rail to rail, without the huge drag that I had experienced previously with the TT & 4" sides.

22

It’s good that your experience with the tiny TT sides exceeds your expectations. Playing with fin configurations can be rewarding. Or not. Either way you learn something. I’ve been doing the fin-play thing for about the last decade of my 42+ year surfing life, when I switched from glassed-ons to Futures sides + Bahne type box for all my multi-fin boards. One of the subjectively most valuable lessons learned was that when I err in fin choice, I much prefer a high-arc launch of my body to the low-arc, skipping stone variety. I usually take advantage of the opportunity to experiment with alternative fins at the end of surf sessions, after my surfing jones has been satisfied using configs that I know work well with the stick I’m using.

Be advised that I consider Halcyon to be correct that fin depth only is insufficient as a standard. Total fin area would be a more accurate, but still insufficient, and more difficult to factor, indicator. Given the plethora of variables, and thus the probably unattainable pursuit of “perfection”, my “quick & dirty” premise is valid and reliable as a guide. Note that while your configuration appears to fall outside my premise relating to depth-only, in reality it doesn’t-the curve of the tunnel adds a bit more than 1/2" to its vertical dimension. For multi PRODUCTION fins, I believe my premise to be a constant. Relative to single fins I’ve decided to amend my premise to a depth + base chord total of 13-15".

23

I think Steve from Infinity has a cluster model that seems pretty progressive in design. The side fins are bigger than the center fin and they protrude outwards. According to Steve this design works with the rails more betta (hahahaha). Does anybody know if this system makes sense or is it just a sham like the turbo tunnel fin?

Cluster: A three-fin design created by Infinity through a rethinking of the function, size and positioning of the fins. Realizing that you turn a board on the rail, We put the biggest fins on the rail and clustered (aligned) all three fins, focusing them at the pivot point of each rail. The V - bottom gives the board “power steering”. The Cluster makes every other board feel unresponsive.

24

paulobaka…!!!

the board you just decribed may have power steering , but in the process the engine was ripped out and replaced with a wind up rubber band…

greg !! i see things a little different in the fin department…(maybe the same,could be interpretation)

i will use your own logic …

what would happen if you had a huge mutant toe???

when you droped it in the water your board would pull radically to one side yes/no?

now lets say youve done your radical hook and somehow you could get that mutant toe off the other rail…then you would do a radical hook the other way yes/no???

you said by putting side bites on,the board accelerates a bit better and turns a bit shorter…

wouldnt it make sense to increase the size of the side fins and get more acceleration and a shorter turn again???

tommorow im gonna post a pic of the fin set up i run on my longboard , huge sides small tail…

the reason i havent been in for a few days is coz ive been competing ,

longboard competition…

the set up i run allows me to go 12 oclock on reos , do super tight layback hacks,and roundhouses and off the foam in the top 1/3rd of the wave …plus when your high on the wall doing hangtime , that fin is pulling the tail into the face of the wave like a plane wing , as its moving forward its pulling one way…sometimes you can nose ride the top of the curl where its basically hollow underneath you , purely coz that big side fin is locked into the lip…(a single would be floating in air)

the large sides allow maximum pivot, with a longboard you need all the help you can get…

regards

BERT

25

ok heres those pics …

these sides work great in this board in small waves…the tall tail fin is better in fat waves ,a bit more stable to walk at low speeds , still turns and drives good …

the smaller tail works better when its small but a bit more punch , i can get the whole back end to let go , not quite the same drive as the taller tail and not as stable to walk , but the extra speed in the waves makes up for that…

regards

BERT

ps i just ran outside then in the dark and took the pics , that box of fins goes everywhere i do …makes for good fine tuning no matter what the waves…

26

I forgot to mention the little bit I posted about the side-bite fin set up was from an advertisement so it wasn’t my opinion. I was just curious to know how you guys felt about this concept. I’ve been riding this cluster fin set up and it feels bogged down on roundhouse cutbacks and in weaker sections (where longboards normally have the advantage) so I must say that I agree with you Bert.

27

Nice pictures Bert!

28

I would also be interested in further input on the cluster setup Paulobaka described in his post.

Bert maybe you can elaborate on your comment to help me understand what it is about this setup that doesn’t work.

Thanks

29

as i under stood it all 3 fins are lined up …so your centre fin sits in between your front fins , all the same distance from the tail,

if we look just at the fin set up for a minute,

doing that , you might as well just ride a twin fin ,when turning on a standard thruster , you either pivot on one side fin or the other , as your turning your tail fin is resisting the turn , if you turn tight , your tail fin is almost going side ways through the water, the further your tailfin comes forward the less lateral resistance there is ,its that resistence you use to drive off , or push off , just like a swiming fish…

so the cluster described would lack drive out of turns , it would hook into a turn quickly , but half way through the turn you run out of steam …

now if we examine the v tail , youve increased your rail line rocker , the further you pull it onto the rail the less resistence from the tail of the board ,same again its that resistence you need for speed and acelaration …the v will give a turn and stop feel …

put the both together and every time you get on the tail and attempt a turn , it just grinds to a halt leaving you dead in the water , you then have to wait for the whitewater or wave to hit you and push you along again…

the v will work in bowly juice where you dont need drive out of turns coz your free falling back into the wave after a turn ,the fins wont like those conditions,

the fins will work for cruising along on a soft wave , the v is not suited to softness …

overall a bad combination…turn and stop , no drive out of turns…

the board will function , you can catch waves on it , nothing really exciting once your on the wave…

regards

BERT

31
Quote:

as i under stood it all 3 fins are lined up …so your centre fin sits in between your front fins , all the same distance from the tail,

Bert,

Thanks for the reply. Actually the way the Infinity Cluster is setup is more like a Twin with a small stabilizer fin. If you read the info on their website it states the fins are "grouped “clustered” nearly in a row " but in reality it is leading edge of the smaller center fin that almosts lines up with the tip of the larger (twin type) side fins. The fins are NOT really in a row the same distance from the tail but that concept has been experimented with by Liddle I believe.

I have spoken to Steve at Infinity who is a super nice guy. I just was looking for some other feedback on his cluster design. He did state you could get the convertible model where you could then ride the board as a Cluster, Twin, Single or 2+1.

I have a lot of years of experience riding a twin fun board and have been looking at the various alternatives (non fish) with a similar ride and the Infinity looks like a Twin with small stabelizing center fin. What I didn’t/don’t know is what the effect of the V would have on the ride experience. I was looking at the ‘Secret Weapon’ model which is 8’ and about 3.5" thick for a small wave or summer board. At 8’ this would be the longest board (aside from a ‘65 Hobie) that I have ever surfed. Maybe I should just go to a full length 9’ longboard but the idea of a loose 8’ board caught my eye.

32

ok if thats the case,no problem , thats my favourite fin set up for smallwaves…

just dont combine it with to much v or any at all for that matter…

that set up works great with a flat or lightly concaved tail and not to much tail rocker…

that fin arrangement helps the board pull hard into a turn , so you do get a pivoty , hooky type of turn…combined with a drivy flatter rocker and you get a nice combination of speed and looseness …

a customer just emailed me today , he said that the big sides in his 8’-6" did this,“ but once you worked the board rail to rail they would go off! You’d get a really good squirt out of the turns when you powered them up plus they would go vert really easy- felt great! ”…

the right tail rocker is critical with this fin set up…you dont want a tail rocker that emphasizes the hook or pivot…

sorry for the confusion ealier…

regards

BERT

33

Greg- I’m constantly experimenting trying to find the right fins for certain boards. I’ve found it really depends on the board. You have aid: “Generally, I use larger more swept side fins with a smaller back fin in flat faced waves and smaller more upright side fins with a larger back in hollow stuff”. I’ve been experimenting the past few days on good overhead reef/point surf the “K” template (which is more upright for the front fins, with a mismatched, smaller slightly rakier rear fin). And then trying rakier front fins but keeping the same rakier smaller trailer. So really comparing upright front fins vs rakier ones with the same smaller rakier trailer. What would you expect to find? (I know what I found- I just want to see if practice matches theory)

34

did you want an answer ??? or were you going to tell us ??

keeping the same tail fin and changing front fins from raked to upright will make a huge difference…

the upright fins will feel stiffer in the trims and off the first pump or two …

but once your up to speed you get sick power hacks in real critical parts of the wave ,still a touch of stiffness you have to fight thru , but that adds to the power of the whole turn , with up right fronts the faster you go the more they work for you…

the upright fin normally gives a pivoty feel , but because you still kept the same tail fin , now what youve done is created a bigger distance between the back of your tail fin and the leading edge of your front fin , thats why there is a touch of stiffness when you work the board,…

the power hacks are created by the more upright fronts as soon as there is an angle of attack they bite harder or hook tighter, the faster you go the more pronounced the hook will be ,

if the waves are bowly with speed , you can go top to bottom really tight , combined with a drivy feel …

the swept fronts will almost feel slower in comparison , but wont require as much grunt in the waves to work they allow you to work for speed and get that speed over a greater range on the face of the wave , they will smoothe the ride slightly , you can take a cutty way wider on the face and still work off flat water to create your own drive,

if you run the uprights to far out on a soft face , it can feel like youve fallen in a hole , you lose your flow and start to blow your timing…

when your going mach speed the raked ones wont allow as tighter hook in the pocket …probably a more boring fin but very reliable …

the uprights have moments of magic but require more mental concentration to know where they work best ,in the right waves the uprights will take it to another level…

the above assessment is only valid if you used a decent board…

regards

BERT

35

Thanks Bert- that was very good and covered it perfectly, just what I was looking for. Yeah, it was a great board I was testing them in, a concaved, super fast but also carvy 6’2. It was not a bowly wave, it was a speed wave. Down the line, as fast and as hard with as much power as possible. The first day I was wondering if the upright combo would be more suited for bowly waves, since hacks were radical but I felt I didn’t get the projection off the first turn as much as I needed/wanted. The switch to the rakier side fins did what I wanted them to do, as you described, increased the arc, smoothed things out, and allowed lots more projection needed in these waves. Big noticeable difference. Really showed once again fin that selection matters. For bowly waves, I’d use the uprights.

36

Hi Greg, we met many years ago when I was surfing at the ESA championships in Hatteras.  I have become very interested in fin technology of late, and just received a patent for a fin system that allows the surfer to drive the angle of attack of the center fin.  My prototype testing has led me to use smaller side fins and a larger center fin.  Since the center fin is able to articulate in response to the surfer’s natural force loads on the tail of the board, I’ve found that the smaller side fins are adequate and further decrease drag as the center fin rudders through turns more efficiently and at a more advantageous angle of attack.

I’d like to get your feedback on this innovation in fin dynamics.  I have been testing myself for a few years now and have settled on the best design and materials, and I will be launching a crowdfunding campaign through Kickstarter.com in a couple of weeks.  To date, I’ve kept the concept close to my chest, but the time has come to innitiate a discussion.  I’ve read your posts on this site over the years, and know you to be a knowledgable and insightful person.  I appreciate your comments.

Thanks, Klaus