Fin theory,tom,halycon and others

General Discussion
261

yep …once again tom your wording is precise and to the point and correct as always…

and to add a few points as well …

a thruster’s pivot point can move depending on which rail you are on ,if you turning hard on one rail your usings that rails fin to pivot off , but as soon as you switch to the other rail you pivot off the other fin…in that process your angle of attack on your tail fin keeps changing from side to side , as long as your tail fin is set to handle that angle of attack (well foiled) it will keep projecting you forward with every pump…that fin arrangment allows you to maximise extra tail area to drive off in small waves…

as soon as you set a thruster in a different direction , it automatically keeps pulling it self around as long as there is an angle of attack, but with a single the rider has to keep pushing the turn…wasting valueable body torque…for a quick transition into the next turn…

tom i think reducing drag in fins is a waste of time…

we should be more concerned with reducing drag in our boards , and increasing the hold of our fins…

what i mean by the comment reducing drag in fins is , the way futures have put a concave on the inside of the fin , reduces drag but also reduces the effectivness of the fin ,so theres an overall loss of control…and loss of hold…

now im leaving the subject a little …

but bottom contours shaped into surfboards to add a measure of control is really only making up for poor fin foils…thats why people note an improvement in performance with a change in bottom contour…

put decent foils in your board and add any bottom contour and see how much worse it goes…

and another comment agreeing with toms comment about keeping the camber forward on your fins…it keeps the water attached to the low pressure side at AOA , as long as your fins are shooting water out the back , there propelling you forward…

hold and drive in one package ,combined with a board shape free of contours shaped in for control,= one seriously fast sensitive surfboard…

theres more …but time is the enemy…as always

regards

BERT

262

OK,

Here’s a thought provoking read

http://boatdesign.net/articles/mast-aft-sailing-rig/index.htm

It touches on a few elements of fins that I’m interested in: the interaction between the two Bonzer side fins; fins made of flexible materials; and fins where the leading edge pivots.

Blakstah mentioned at surfermag that Greenough was also interested in this last point. Blakstah, where did you hear this. Dale, you know anything about this interest.

I also think we should look to the more innovative sailboard sail makers. They have made a few tweaks to traditional designs too.

Rob

263

I think Roy has created his own garden path, and I admire anyone who carves their own track, having few peers.

If “high performance” is defined as the best surfing of the world`s most successful competitive shortboarders (and their equipment) in the most challenging waves… then all else pales in judgement.

“High performance” as defined within a personal context is an entirely different issue.

264

agreed there dale…

and no maliciousness meant for roy…he has definatly added to the range of knowledge and has showed some interesting concepts , plus made some inteligent remarks…

i was simply showing the other side of the coin…

every design has a positive and a negative…in the end it comes down to how much fun you have …

but really for any design to be accepted by the mainstream then it has to be proven by competition…if it really is good it will prevail…

plus even competition has branched into many areas . so it could establish itself in one of these areas…

arial comps, big wave , tow ins, longboard,shortboard,boogieboard…

if its really fun you could get a whole new class of surfcraft…

regards

BERT

265

Bert,

I hear you! For example, Roys equipment and mine couldnt possibly be any more different from each other. I have no desire whatsoever to ride a 70 lb. 14’ board. But I totally respect what he`s doing.

At best, “Mainstream” is a dubious distinction.

Whether perceived as good, bad or benign, the “mainstream” is ruled by whoever has the most numbers. Ultimately it translates to far more money spent on advertising, trade shows, teams, competitions, associated soft goods, etc… than actual product.

When I hear “mainstream”, I think of companies like Morey Bodyboards and Surftech.

On the opposite end of the spectrum… I build surf mats for Dave Rastovich, arguably one of the finest non-competitive shortboard surfers in the world.

266

Tom, a couple of comments - I’ve ridden the CRVs quite a bit (as well as their predecessors in the 80’s) and have given up on them for steep faced waves, where they don’t work so well. I don’t know that adding a winglet would help with that problem, but would be interested in hearing how it turned out. I’ve been thinking of winglets but never on a curved fin, why would you start there? (Especially the CRVs, they are relatively upright and winglets should have a more pronounced effect on raked fins…)

Second, does your thinking lead you to conclude that foiled fins should be thicker first, then foiled, to avoid the loss of high AOA performance? (or am I misreading your argument?)

267

I think that CRV’s have too big a plane form. I believe you could shorten the cord length considerably and they should work better in bigger steeper waves. But, that’s not really the direction I would develop that design towards. I believe that you could get a better lift to drag ratio with smaller curved fins with an end plate, because as you transition to up on rail the lift vector will stay normal to the wave surface. Shorter cord lengths would minimize drag and a gredient lift vector normal to the wave surface will optimize fin hold at higher flow rates. Finally, I believe that the endplate will minimize tip vortices drag withou relying upon rake or a diminishing tip foil. But, I have yet to prove my theory with models.

Second, I believe that the girth of a foil is a tradeoff. At higher flow rates more girth means more drag. But, at lower flow rates more girth forward on the foil means a greater range of AOA prior to stall. So, if you intend to ride big waves with controlled flowing turns, it’s better to have less girth and the apex of the foil further aft and more rake. Whereas, if you want to surf with abosolute reckless abandon, yeah more girth farther forward and a more vertical template is a good thing.

268

Here is an interesting collection of unique fins:

http://www.surfresearch.com.au/f.html

I thought this was an interesting concept. I still want to try something like this but I’ve resigned myself to starting much simpler, and try and work out some basic principles for myself. I’m having a hard time envisioning how those small endplates would act on a board.

I’ve been riding the CRV’s for a couple years now in Florida. I really prefer them in my smaller, thicker summer board. The large plan shape has a lot of drive yet they are still loose and responsive. I have them now in the front of a quad setup with longboard side-bites behind them. It’s an intersting setup because the smaller rear fins almost bisect the CRV when you look down the stringer at them. I’m sure this is doing all kinds of weird hydrodynamic things, but they work well for me in knee high summer surf. I’ve ridden them in my mini-gun in some hurricane surf which here in FL tends to be pretty slopy and not as critical as other places. They loosened up the board a lot, but still had a lot of hold and projection. It was an intersting experiment but not the set-up I prefer for bigger waves here. They don’t work so well in hollower waves.

Here’s one for you Roy:

Tunnel fin, circa 1964

269

Damn those fins bring in alot of the characteristics of what we’ve been discussing without the curve. I’d be really interested in getting my hands on a set of those to check out. Lawless who made those fins?

270

This is all it says next to the photo:

1986

Split Wing Assymetric

Molded plastic

Thruster side fins by Multifins

Fin box.

tomatdaum, take a look at that link I posted above, lots of really interesting stuff.

271

Yeah I did a search and it appears ParkesAustralia maybe a contact. Midget Farrelly apparently has them make Malibu Fins.

272

here’s what it says:

1986

Split Wing Assymetric

Molded plastic

Thruster side fins by Multifins

Fin box.

273

Hello Keith,

Thankyou for your comments. The main handling problem which I experienced with flat plane hydrofoil winged fins was that they would suddenly twist the board when inthe tube. However I have not used one of Cheyne’s fins which are set up a little differently.

You mention a ‘vertical lift problem’. I have never said that there is such a thing. I believe in horizontal fin surfaces which create vertical lift! I have simply pointed out that there is vertical flow and pressure on a fin which needs to be taken into account when analysing tip flows.

I am certainly not trying to show that “all other systems are defective in order to show that a particular one has merits” I spent several years working on flat plane hydrofoil fins and fully believed in their potential. I did this work nearly full time in the most appalling circumstances, and was ridiculed for my efforts by all and sundry. I am just reporting my experiences, and the problems which I had with these flat plane systems.

Regarding the right sized tunnel for a little thruster, I am sure I don’t know. I personally find that it is difficult to control the fore and aft trim of a shortboard sufficiently well to control a horizontal wing and the resulting lift. I have therefore been very cautious in suggesting that such wings will work on shortboards. But then I am a longboarder.

Roy
274

Hello Bert, Let’s hope that this active discussion is doing you good!

How is it possible to '“absolutely say for a fact” that a board with a tunnel is unable to do 180 degree turns? How is it possible for you to establish an absolute fact without either experience in the matter or theoretical support? I am not allowed to get away with that kind of thing, I have to support what I say. So I cannot, therefore, accept your statement. If you asked me I could tell you about how well a tunnel fin turns.

The asumption that seems to be creeping in around here is that tunnels are only good for straight line speed. I cannot find the source of this erroneous idea anywhere, and I wonder where it came from. Is it perhaps because I have published photographs of tunnels on long pintails? If so the conclusion that tunnels only work at small angles of attack doesn’t follow.

Tunnel fins turn so fast that they can buckle your knees with the g force mate!

You also assume that I am trying to get tunnel fins accepted by the mainstream. Not so. The tunnel fin gives me such an advantage over the opposition (In terms of speed, holding power and even maneuverability) that I am not really going to be all that stoked if the others start to catch up. Your comment that I should ‘get’ Kelly Ryan or Mickey Thompson to ride my boards is laughable. This is a public forum so I can’t say too much, but may I just say that I am not impressed by their noseriding antics or slow tail pivots.

I now refer to your comment that my boards have been relegated to the garden gnome and magic mushroom

corner. I take it that what you mean is that the boards have not been proven in competition. Well, I can say that I have been proving them in informal competition around here for quite some time and that’s good enough for me. Plenty of puffed up little comp heads have gone away muttering sad things after having their tail feathers roasted by a Power surfboard!

By the way, I lived on the point in Raglan for three years and can honestly say that I found the waves a little slow. Don’t you agree?

Speed is everything.

Yours Faithfully, Roy R Stewart

275

Tom…see boardfolio.com/surflinks/surfboards. There’s pics of a number of fins from yesteryear.

276

Thanks Laconic,

 I've got boardfolio and surfresearch as favorites. I just had not seen those paticular fins before.
277

i’ve watched this thread from the sidelines for what seems like months, but feel compelled to respond to a quip by roy in one of his many long replies…this one invlolving his hydrotheoretics on starfins (and winglets), what they are lacking, and dismissing with a wave of the of hand (or cursor) that the “proof is in the pudding” argument is heresay, therfore not relevent…

has everyone forgotten who designed that fin??? BEN LEXCAN!! a naval architect of impeccable credentials who revolutionized america’s cup racing design in '83 with his australia II (with a winged keel) blowing everyone out of the water and bringing the cup home to OZ. no offense to all the backyard (or back of the van, bus, or tent) designers and tinkerers out there but this guy forgot (before he died, RIP) more hard scientific hydrodynanic theory than you’ll conjure up in 10 years of message board forums…

i’ve ridden a starfin in any number of my boards since 1985 and to this day feel it’s the most progressive single fin ever developed for high performance shortboard applications. does it work on a 14 foot wooden paddle board? who frickin’ cares? 99.999% of the surfers on this earth will never ride a board like that , nor have any desire to do so.

so yeah, the “proof IS in the pudding” and until your latest spin on a 38 year old concept is actually used on equipment comparable with what 99.999% of the surfing populace rides, is proven, and found superior to what’s currently “working”, this comparison of apples and oranges is becoming increasingly wordy (like it’s not already), and IRRELEVENT.

(no offense intended regarding your work, your design, your craftmanship, or admirable dedication to what you feel works for you…but this whole thing is eerily FAT-PENGUIN-esque. if you weren’t on sways’ the last couple of years you won’t get that but everyone else will)

regards,

jim

278

Hello Jim,

Your reference to Ben Lexcen and his credentials is just the old ‘argument from authority’ which is always fallacious. Try taking a basic course in logic.

How on earth can you report on how much hydrodynamic theory I have between my ears? You really haven’t the foggiest idea. And please be careful casting doubt upon my work because it comes out of a tent. Ghengis khan lived in a tent, so watch your mouth, I don’t hassle you because of the way you live.

Yeah, and you’ve never ridden one of my boards and you are passing judgement on them! This is unreasonable.

Why should I care what 99.999% of riders do? How do you know that no one wants to ride big timber boards? Go and check out Tom Wegeners sixteen footers, you will be seeing more of them and boards like them in the future.

You say 'No offense" but if you really want to avoid being offensive then stop getting so upset.

My boards are surfboards not ‘paddleboards’, and they ride waves very well.

If you are annoyed at my ‘Wordiness’ then realise this: I will continue to defend the truth and myself as long as I am attacked.

Yours Faithfully, Roy Stewart

Ps You can stick your ‘impeccable credential’ theory in the waste paper basket where it belongs.

279

before this gets out of hand …

id like to say sory to roy for placing his work into a box…

i hope i havent started a negative vibe going here, if so it wasnt my intention…

personally ive seen roy present some logical points on hydrodynamic theory…

but i dont think you need to build every concievable design concept into a working model, just to test whether it would be functional or not…

thats where understanding the basic principles come in …

i still stand by my comments about not being able to complete a series of 180 degree turns in succession…

based on current established principles of hydronamics,

as far as some of my other comments about competition performance…

that just comes down to who’s rules or critirea your judging performance by…

as a general rule , the majority will always be the factor in what is percieved to be high performance…but that still doesnt make it right or wrong ,

coz surfing is an artform , there by making any performance comparisons , entirely subjective…

regards

BERT

280

Hello Bert,

Apology accepted,  And please accept mine for making so much noise around here. It's just that a man's gotta do what a man's gotta do!   

I am always very interested in what you have to say, Bert, and I must say I have learnt a lot from everyone on this forum so far.  

I am thinking about your assertion that the tunnel won't do 180 degree turns. Perhaps you say this because the tunnel is parallel, and has no toe in. It could then perhaps be expected to behave like a parallel finned twinfin fish, which isn't supposed to be very maneuverable.  

My experience has been that the setup is very loose and will in fact 'turn on a dime'. I don't really want to force the issue any further, except to say that I too, stand by my claim.  

Sincerely, Roy