Thick fins vs. Thin fins

General Discussion
121

Rich,

Funny should mention the psychodelic single. I have not ridden it since Nov. or so when I found it road small mini tubes quite well with the fin you made me. I’ve been eye balling it again and decided to put a leash plug in it to surf it in bigger more crowded condition so as not to injure anyone. I’ve been in a fish thing for a year and have made a couple this season including a 5’10" I rode for the first time last week in fun chest high stuff. I also built a 7’2" single that I don’t really like, but haven’t given up on and a 7 foot 2+1 I haven’t given a chance, yet. I built a 6’4" fish that is o.k. Concerning shark evolution. What’s a couple hundred million years between friends? Huh?

Mark, Thanks for the clarification on Reynolds number. I’ll skip the equation and run with your description. The tunas are incredible fish. Fast and maneuverable. Swim their whole lives from one end of the ocean to the other. Yummy, too.

All my homemade fish fins seem too thick to me. Definately, thicker than the fins on the Mabile’s I’ve seen or the Gephart’s. I’ve been getting thinner with each board. Most seem to work pretty good, however.

Daddio, I dig bumble bees and all the other bees. I’ve seen some of the slow mo film on the nature stations. Amazing. Mostly, I like to listen to them and watch them working over my garden. My Calif. native plant garden is full of em.Mike

122

“…in regards to foam glassons vs plug/box systems, have you considered the effect of the plugs themselves? Meaning, the plugs not only add weight but also structurally tie the deck and bottom skins of the board…thus flex/shear movement between the two sides would be ‘different’. Seems like there would be multiple performance advantages to using glassons”.

Yes. I’ve known for a long time all the best boards I’ve had have used foam core glass-ons. I much prefer the lighter weight and feeling of whole-board tuning like a tuning fork. Fin systems are something I’ve learned to put up with for three reason: I can pack more boards in a travel bag easier with no fins, I can experiment with fins, and when traveling I can avoid messy and time wasting fin repairs if they get chunks ripped out on dry coral reef heads. I’ve also recently come to question whether everybody can consistently accurately position either glass-ons or plugs these days, though.

123
Quote:

Racing yachts go to extreme lengths to keep weight out of the ends, or the perimeter. There are huge equations (and some simple ones) that describe the effect of weight placement and natural frequencies (uh oh back to that) but basically the effect of moving any weight two feet from the center of gravity is four time that of moving it one foot. In a nutshell concentrated weight is a good thing for performance.

simon …

put the spring where it will be most effective …

and make sure the fins can stand the extra load and aoa from the twang …

the more vertical the wave face the higher the aoa just triming …

gentle pumps will generate mach speed if your fin can handle the aoa in the first place …

this isnt a racing yacht , id say , the yacht guys probably know what there doing when it comes to yacht’s …

i build performance surfboards that rely on the ability to generate as much speed as possible , i would welcome opinions from anyone else in the same field …

but it seems to me theres not many takers in this field yet …just business minds and marketers …

man i wish i could load some frame grabs from a dvd i have of this guy …

he won his first national with 14mm thick fins , and was generating more speed than anyone thought was ever possible on a surfboard …

my only advice to any enquiring minds , seek without presumption …

ive got some more wilderness to explore , this time gonna take a few team guys and some cameras …

seems all this remote space and waves and isolation from the rest of the worlds surf scene has actually protected us …

stoked to be free and outside the box …

is the kid in the wilderness really lost ? or are the people in the city just confined within there self defined boundries ?

regards

BERT

124

Bert, I always thought that being away from the power structure of the sport did have some advantages. FL is not generally seen as cutting edge and yet we have raised a few noteworthy prodogies over the years.

As for weight distribution, there is a sigificant difference when weight is shifted forward and aft. We actually would add weight to the nose on some designs to increase the upper range. In that way we could push short small wave designs into larger surf. Lead shot was used for this. Changing the fin set up from straight three to a more 2 and 1 (shrinking the sides a bit and growing the back fin a bit) would also allow more range upwards.

What I’ve found over the years is that some guys have real trouble in moving to a bit more board in larger surf. Taking the same design their used to in everyday conditions and pushing the range up using weight distribution and fin alterations can sometimes be a more effective method for these guys. I used to shape them the exact same board, make the alterations and give it to them as their big wave board. Didn’t even tell them what I’d done.

125

Mark, I made some suggestions a couple of months ago to the blokes at Swansea along the lines of “a common vocabulary” and some basic coefficients that might relate to surfboard performance. It seems to me that there is gap to be filled between the ultra-theory of academia, and the real world craft of surfboard design. Maybe Swaylocks is the place to start.

I would never profess to be more than a keen amateur when it comes to surfboard design, I don’t even know what really works for me (I do know what doesn’t work though!). And I do have a good education in a related subject, and years of professional design under my belt. What strikes me about surfboard design is the lack of a common frame work by which a surfboard can be described, both technically and subjectively. Without this, which is common in the vast majority of engineered product fields, surfboard design will allways rely on a very few enlightened individuals willing to step out of the mainstream.

Might it not be feasible to write a Swaylocks white paper operating under some licenese similar to open source software, proposing such a framework?

126

“What strikes me about surfboard design is the lack of a common frame work by which a surfboard can be described, both technically and subjectively.”

kind of agree and disagree…the common design framework is out there but its not consolidated into a ‘handbook’…thanks to Sways one can find the pieces of the puzzle and connect the dots as I have. The real challenge is the subjective and non-subjective testing of equipment…I rode my majic carpet again yesterday and most waves the board does its majic but on other waves the majic is lost…I attribute that to wave selection and foot placement…

Definitely going thicker on fin sets too…

127

“What strikes me about surfboard design is the lack of a common frame work by which a surfboard can be described, both technically and subjectively.”

"kind of agree and disagree…the common design framework is out there but its not consolidated into a ‘handbook’…thanks to Sways one can find the pieces of the puzzle and connect the dots as I have. The real challenge is the subjective and non-subjective testing of equipment…I rode my majic carpet again yesterday and most waves the board does its majic but on other waves the majic is lost…I attribute that to wave selection and foot placement…

Definitely going thicker on fin sets too…"

I agree. On one level there has to be some commonality in existence already or CNC machining would not be possible.

But how surfers are describing that they feel or how they think their board works, or how their fins are interracting with their boards to be creating what they think are board problems, and the apparent interchangability of their use of terms could stand a little defining.

WE now have two suggestions that Swaylocks.com is perhaps a good place to start this process. I am wondering if anyone has a suggestion as to how to proceed? I myself have looked at the A-Z glossary on Surfline.com and looked at the major fin company sites to see how they describe their fins. This preliminary investigation indicates there is a long way to go, but it would be a good idea if we could decide on the size and shape of the table first if you know what I mean. Don’t want the process to alienate. My suggestion here is that Swaylocks is a round table which anyone can sit at and contribute to. I could stop here. Or: Next problem is who decides if a term should be considered? Or, is there to be a leader? That is enough for now. I’ve gone too far. Mark

128

it all depends on the purpose of such a frame work …

anyone with some patience can find some real gems in here …

anyone with an interest does join in on what they feel comfortable adding to …

are we seeking to establish blind rules of design ??

coz one problem there is the interaction of every facet of design …

one example , extra cant , it slows some boards but makes others faster , depending on rocker and rail configuration …

so what does extra cant really do ???

a common language for cnc is essential if you want to send a digital design to another machine and have it copied , but a common platform for board design would be far more complicated in the sense of all the variables …

i agree its a good idea …

do we pick appart every facet of design till the verdict is unanimous ??

do we discuss every facet of design to establish basic facts based on known repeatable experimental data , combined with anecdotal evidence , and then add all of the possible variations to any excepted known design fact ?

if that is the case , you need a more controled enviroment , discussing specific design variables , without the distraction of passers by throwing in there 2 cents worth …

i dub thee SIR Surfalot , you are worthy of sitting at the round table …

hey swaylocks is doing it again … definatly the place to start ,seems most of the real creative types seem to be gathering here …

good ideas , seem to gather there own momentum if everyone is enthused …

regards

BERT

129

i agree with the spirit of your suggestion but still it would be a challenge…give two people the same exact board and get two different sets of feedback…one says tomayto the other tomahto…

something that’s intrugued me for a while is loosly defining all variables to some usable format…when you consider all variables including style, waves, design, construction, fin configuration, fin design, etc etc…seems like a daunting task…doesn’t it? I think thats the place to start if someone wanted to develop a handbook.

PS - regarding positive buoyancy fins and its affects…wouldnt you get the same result by thickening the tail section a bit? I think thicker foils would have a more pronounced affect regarding board lift characteristics…

130

I agree that a standardization of terms is the best way to progress design as a community. However, I don’t think we should try to reinvent the foil. Surfboard design has much in common with aircraft and naval architecture and has borrowed terms from both. Where we get confused is with the misuse of terminology and taking marketing descriptions and holding them out there as scientific investigation. Take the term cavitation. Surfers have misused this term for decades to describe stall across your fins. The reason could be because we already use the term stall to descibe the momentary hesitation of forward progress of the board by sinking the tail. Or, it could be because you get that similar rough stutter feel under your feet when your fins stall as when a boat props cavitate. However, every accomplished surfboard shaper understands that the flow across the fins has become detached when their customer says they are feeling cavitation. I believe it’s a matter of educating those that are interested. If you want to make it easier, create a glossary. But, the terms in the glossary should be scientifcally derived and not just marketing schpeal.

131

One thing I’ve noticed about this thread, and others, is that the round table idea is slowly getting lots of chairs and becoming bigger naturally.

For a while, and there will be more for sure, people, and I must include myself, had very self centred opinions of their board and fin designs. That’s fair as we all are on our own trip, and conclusions are fully relative to our own experiences, performance and expectations.

Of late more ideas discussed are overlapping, the manufacturing is a perfect example, with, as Bert points out, incredibly good results.

Design is a little different. I’ve used my own bottom design and thick fins for a while now and do not feel the need to go back to try things over again just because someone else finds it earth moving. What works for me may not work for someone else. However I don’t feel it’s my place to be critical of others learning very similar lessons, even if their results are different.

The bigger this online discussion table gets, the better off we all are.

The Swaylocks round table allows everyone to meet head on at a common ground, and everyone gets their chance to speak.

There should be no leader, that’s falling backwards again. Guru and legend are two of my most disliked words, and the ‘leader’ would run the risk of flack from the masses. There is no head at a round table.

Everyone who sits around this big round swaylocks table gets lots of chances to carve graffitti into it, with lots of great ideas. Luckily I can sit here, we all can sit here, check out all the carvings, not even have to say a word, and get up and leave feeling we’ve learned some more. And we don’t have to sit in the same spot each time we come.

I just carved a big ‘W’, but if no-one sees it I won’t lose sleep.

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Quote:

PS - regarding positive buoyancy fins and its affects…wouldnt you get the same result by thickening the tail section a bit? I think thicker foils would have a more pronounced affect regarding board lift characteristics…

Board thickness doesn’t relate so directly to buoyancy while up and riding, because water doesn’t wrap around the top. Thin or thick, if the down rails are shedding flow, its all the same.

A little wider would increase buoyancy though…

I’ve been hacking on the fraction of the rider’s weight supported by buoyancy (water displacement) and the fraction supported by planing forces…

133

Hey Tom - re your comment:

“I believe it’s a matter of educating those that are interested. If you want to make it easier, create a glossary. But, the terms in the glossary should be scientifcally derived and not just marketing schpeal.”

For those who haven’t noticed, at the top of your Swaylocks page is a menu item “GLOSSARY”. We have tried to keep it accurate, scientific, and free of BS. But it’s also an open entry system, anyone can contribute, comment, update and improve it. FEEL FREE TO DIVE IN GUYS, Use it and make it better!

134

Okay here’s a perfect example. The glossary describes Cant as: “Cant is the angle a fin makes relative to the bottom of the board.” However, a number of shapers I’ve worked with will take their cant relative to an imaginary plane perpendicular to the stringer at the center of the side fins. If you make your cant relative to the bottom of the board, boards with vee will have a greater angle of cant relative to horizontal and a board with concave will have less. And, a blank with twist is just a fricken nightmare.

135

Good answer, Sir Bert of the Wooden Twanger… we need more voices, not less!

OK - next assignment, my little academia nuts (green egg and hammers), is to study Greenough’s spoon and his paddle fin design and make a mental note of THE COMMON FEATURE(S) OF BOTH DESIGNS. How does thick and thin AND surface area relate to both.

EXTRA CREDIT:

Chip in, buy a computer/laptop and get a designer of surfboards (or manufacturer or anyone involved in fluid dynamics - theory or practice) online and get them interested in SWAYLOCKS.

Answer this question: Did God/nature roll the dice and throw out any flight-full heavier than air beings already?

Answer this question: Is bottled up knowledge in your head similar to white papers and the like (mass)? AND why does this traditional process slow the transfer of knowledge? (ripples and waves, separate entities or blood brothers?)

SUPER EXTRA CREDIT:

Get a friend interested in ANY forum environment that allows them to contribute to the wave like sharing of knowledge/experience.

Get Greenough online and jacked in!

If you blurt out answers and concepts and ideas and questions, say a prayer that those with the knowledge/experience will help you just ONE MORE TIME.

AND that someone will create an index (yearly?) in text or pdf format that will organize Swaylocks (knowledge/experience) and could be purchased on CD(?)

136

I have often heard he term cavitation used and I have heard it misused. We should ahve a proper definition for cavitation. Any takers? Tom? Could you clean up tht one? I would like to nominate the term ventilation. I first heard this term used by Greg Loehr. So I think he would be the one I’d like to start the definition for ventilation. Greg?

137

The way I see it, the more self directed the selection of terms is the better off we all will be. However, it is necessary I think to keep mindful of and faithful to the already accepted definitions as they relate to the fields of aircraft, hydrodynamics, hydrophysics and nautical architecture. For example just because one person (and I don’t mean anyone in particular) stands on his or her use of the term “lift” there is no way that this will be acceptable to the majority. So if we can relate each term, we wish to define, to already accepted definitions, that will help.

As in term “cant” which can be made better, Tom has already started to address this problem. Perhaps the procedure he instinctively used is the best one. Present your term, iterate it’s current definition. Give reasons why that definition is not adequate or wrong and suggest a way to improve it.

IF a term can be traced to a first source we should do that, too, whenever possible as in the inventor of “concave” being Greg Loehr, a claim supported by Surfing mag’s Nick Carrol and Australian shaper Greg Webber.

Standardization of terms can only improve our descriptions and analysis.

138

Mark, I posted a definition of cavitation in another thread.

139

Keith,

Great idea.

What is made here should stay here.

I still think having a moderator would be very helpful.

And a resident expert, too. I would like to nominate you, Keith for moderator, since you already are familiar with the roll.

For resident expert I’d like to nominate a man who was the shaper for a little known surf and skate team in the mid 70’s through the 80’s. It was this team that perhaps landed the first air tricks we now know as aerials in both skate and surf. This team developed talent by nurture, competition, and innovation. This shaper developed a board design that has since become the industry standard short board. It’s lineage is simple. Loehr to Kech to Kelly to Merrick. The shaper Greg Loehr. He has written extensively on the subjects of board design, fin design and balance theory and he knows pretty much who developed each part and is not above giving credit. If he just participates we will be lucky.

140

Mark Spindler: “…IF a term can be traced to a first source we should do that, too, whenever possible as in the inventor of “concave” being Greg Loehr, a claim supported by Surfing mag’s Nick Carrol and Australian shaper Greg Webber”.

Hmmm, I hadn’t heard this one, and quite frankly with all due respect to Greg Loehr I don’t believe it. As for Nick Carrol being credible, give me a break ( and didn’t Greg Webber start shaping decades after the term was first used…)