# On rocker, rail, template and fin... and stance

The comments of M_Woo and obproud needed to be liberated from one of my threads that is rapidly becoming a tome, or is that tomb.  Anyway here they are. I’ve trimmed obprouds post down a bit, hopefully he’ll won’t be too pissed. kc

obproud’s post (trimmed) … originally posted in “Trade-offs: Modern Toed/Canted…”

This brings me to another idea that I have been pondering, but have
not read much about. That is, that rail curve and rocker curve really
represent ONE curve, in 3D space, (even though we generally think and
talk about it as two separate curves) and it is this curve and it’s
relationship to the positions of the fins that determines how the board
is turned, and how speed is produced. With the same fin orientation
(cant and toe), but a different rail or rocker curve, the rider will
have differing ability to change the AOA.

What I mean is that it
is more about the angles between the rail/rocker curve and the fins,
than it is about the angle between the fins and the centerline, because
the rail/rocker curve is what determines the orientation at which the
fins can be situated.

M_Woo’s post in reply to obproud’s… originally posted in “Trade-offs: Modern Toed/Canted…”

Aloha,

While this seems off the subject it’s directly related.

obproud: This brings me to another idea that I have been pondering, but have not
read much about. That is, that rail curve and rocker curve really
represent ONE curve, in 3D space, (even though we generally think and
talk about it as two separate curves) and it is this curve and it’s
relationship to the positions of the fins that determines how the board
is turned, and how speed is produced. With the same fin orientation
(cant and toe), but a different rail or rocker curve, the rider will
have differing ability to change the AOA.

I
COMPLETELY agree with this. The 3D curve that the rocker and template
make up is one. Thinking of it as 2 seperate things just makes it a
little simpler to measure and reproduce. How much water the rail
directs past the fins is a huge factor on chosing fin placement and fin
size.

Let’s use a 5’10 as an example. You could make one for
use in 2 foot surf or 25 foot surf. The rocker and template for the
5’10 made for 25 foot surf would be flatter and have much narrower and
straighter template because you would be traveling in such a long arc.
The curve on the face of a 25 foot wave is much larger. Also the fin
placement would change as well as the fin size.

The 5’10 for 2 foot surf would have more curve in the template and rocker. As well as a fin set up for turning tighter arcs.

Another
thing that will influence the fin set up is the shape of the rail and
how far up the board the edge runs. Imagine if you sanded off ALL the
edge of the board all the way back to the tail. The board would have no
drive at all. You would need the fin/fins to make up the drive. Run the
edge all the way up the rail to the nose and the board becomes tracky.
Where the edge fades in relationship to the surfers stance is key to
producing user friendly boards.

So back to the point I was trying
to make in my first post. Rocker, template, bottom design, foam flow
will dictate or should dictate where you chose to place your fins.

At least it does for me. =)

Mahalo,

MW

So, I just checked the surf and no
waves. One thing that crossed my mind while driving to the beach. I’ve
always thought of the template as the effective edge in the water.
Snowboarders use that term " effective edge" for how much actual edge
is engaged in a turn. The medium that they board on ranges from ice to
powder. They use no fins. Have you ever seen how far on rail a
snowboarder can get in powder without fins. There has to be something
there. Prob. the template and flex of the board and the sharp edge. (My
apologies for using snowboards for this example) I always try to keep
an open mind and take information from every source I can.

There
have been attempts to make surfboards finless and although you may be
able to ride a finless board. It would be far from out performing a
normal “thruster” fin configuration. I have been actually trying to
reduce the amount of fin area on the boards I make. Rocker and template
changes were the first things I did. Moving the trailing edge of the
side fins closer to the rail was just one of the things to combat drift
or cavitation on a bottom turn. Concave through the tail also helps
redirect the flow of water through the fins more effecient. (Using my
normal shortboard as an example: 60 X 18 1/4 X 2 1/4.)

Also
just to touch lightly on this. I believe the foil on the side fins help
keep the rail engaged in a turn. And just for the record I’m not a fan
of concave fins. Flat/single foil seems to be the right “balance” for
the amount of lift needed to keep the rail engaged. More lift is not
always better and it does not always equate to speed. Balance has
always been the key for me.

Mahalo,

MW

Very interesting ideas that have been put out there. Def. a lot of food for thought and I know I will be mulling this over for quite some time to come.

MW - How close are you putting the side fins to the rail to keep the balance and what results have you had so far? (if you are willing to share. If not no worries)

Thank you for the putting your thoughts out there and also thanks for seperating them out so that they could been seen as stand alone ideas.

Aloha CHarvey,

Hmmmm… For a normal thruster set up with my templates, rocker and bottom design on a 6’0 X 18 1/4 X 2 1/4. The side fins are at 1 inch off the rail 10 3/4 up from the tail. The tail fin is at 3 3/8. Side fins point 1 1/2 inches off the nose on the side that fin is on and tilted about 7 - 7 1/2 deg off the concave. This setup is very user friendly and has the right amount of bite for a solid bottom turn with the right amount of release in the lip.The fin placement changes with the length of the board.

On the other end of the spectrum I have a 7’6 that the side fins are 3/4 inch off the rail. This is just what I’ve found to work for myself and people who ride my boards. I sure don’t want any cavitation/slipping on a bottom turn when I’m riding a 7’6. I’m also not doing snaps and trying to throw the tail on a 7’6.

I always tow the forward fins off the nose with a flexible straight edge. Much more accurate then towing them in off the stringer where the front of the fins are because stringers are almost never straight. I mark the back fin, run the straight edge to the nose and draw a line to make sure the rear fin is straight. I never trust the stringer to be straight. =) Hope this helps! =)

MW

I'm curious, when you write that you moved the trailing edge closer to the rail, I guessing you're not talking about toe alone, but that you've widened the configuration or relative separation of the laterals. So how are you setting toe? In fact when you do this kind of adjustment, are you inclined to make any other adjustments, e.g. move them [laterals] slightly forward or back?

By the way, as for finless boards, the point I seem to obsess on is that virtually everything else after you've got a minimum amount of planing area, is geared towards user-friendliness. I believe the same intent is embodied in your use of the word 'perform.' I'm simply not always sure that this is understood, or maybe not seen in these terms.

kc

(in edit 07/17/09 - apologies... this was typed up off-line earlier this week and mindless posted this morning.. at least it was short)

“rail curve and rocker curve represent one curve…”

While I commend your heady musings here, I think your need to conceptualize leads to a gross oversimplification. What part of compound curves aren’t you getting? The effect of the combination of curves may net ONE result or action, but the curves are not one curve. Simultaneous curves existing in “3D space” are what they inherently are…a combination of curves.

ALL the curves in a surfboard cannot be dismissed for any one single supposition, to do this would dismiss all the variables that contribute to the isolated concern you address and have yet to be quantified; perhaps never will. This is how and why the great debate on surfboard design rages on between artists and scientists. The latter group attempts to explain it all away therefore making it fundamental, while the previous group contends with the individual combining of those curves for each individual with its subsequent successes and failures…likening it to artristy.

The artist making the board takes imput (not unlike an impression) then paints the board based upon those impressions. Because the impressions are as individualistic as there are people, the artist producing the board combines those curves in different compositions. Yes there are many that are similar, or even reproduced with machines, but the combination of those curves make up the totality of the piece.

To isolate one aspect of a surfboard like rail/rocker curve and the fins and state that it is more about this orientation versus the positioning from centerline is simply that…a statement, supposition, guess that may even be an educated guess but is one you wil be hell bent to quantify.

How will you go about that?

Dissect all you want, but give all the curves inherent to a surfboard their just due: foil, volume, rocker, rail, deckline, bottom contours, fin outline chord etc…compounding curves…infinite possiblities…that’s what makes it fun!

P.S.

Some things are better left magical & mysterious, at least to some of us. Elimination of surprises in life would be boring…

yeah very clear

what i do is calculate the toe in in degrees based on the info i have [a lot of times the toe in seems to be 1/4 inch, or 2,5 inch perpendicular of stringer at the nose… a lot really…

then, i define how much toe in is needed in width over a length [along stringer] of 3 foot. then i lay down that width and mark a line that passes

just my 2 cts

that way i always get a decent fin marking for one fin. same goes for the other fin of course.

yeah very clear

what i do is calculate the toe in in degrees based on the info i have [a lot of times the toe in seems to be 1/4 inch, or 2,5 inch perpendicular of stringer at the nose… a lot really…

then, i define how much toe in is needed in width over a length [along stringer] of 3 foot. then i lay down that width and mark a line that passes

just my 2 cts

that way i always get a decent fin marking for one fin. same goes for the other fin of course.

I don’t understand how it is a “gross oversimplification” if it is the reality. We live in a 3-D world, but our brains process what we see, and what we think in 2-D. We use special visual cues, like size, clarity, speed of movement, to reconstruct the 2-D image into a 3-D representation. It is easy to think in 2-D, but it is much harder to think in 3-D, that is why IQ tests always have a portion devoted to matching up the same 2-D representation of a 3-D object from different points of view.

It is very intuitive to think of simple curves in 2-D space, but it takes practice (or a more naturally developed visual cortex) to accurately visualize things in 3-D. It is also easier to take measurments when only considerting one plane at a time. BUT, in reality, things (in our case the wave, the surfboard and the rider) are operating in 3-D space. So, I think, that if you want to approach a “true” understanding of what is happening you have to consider what is happening in 3-D, and you have to think of the curves as 3-D.

I think that it is easy to get locked into thinking in 2-D since all of our measurments are taken one plane at a time. So I would argue that it is not a “gross oversimplification”, but, rather, a simplification (that is not so easy to simplify) that lends insight to what is REALLY happening.

As far as the scientist vs. artist, left brain vs. right brain, I would argue that thinking about one curve at a time (i.e. tail width at 3", 6", 12", 18", or tail rocker at those positions) is a more scientific/left-brain type of activity, whereas thinking of one wholeistic curve is more of an artistic/right-brain activity.

I like to try and think in both manners, and blend the two, hence the “heady musings”.

The physics of what is happening on a wave and under a surfboard don’t change, the physical laws stay the same, wheather we understand them or not. The physics/reality is there, and it is our job (a purely human endeavour) to try and understand them. We do this by deconstructing the parts (left-brain), and then try to put them back together to gain a better understanding and a wholeistic view (right-brain). Synergy: The whole is greater than the sum of the parts.

What I am getting at when I say that “it
is more about the angles between the rail/rocker curve and the fins,
than it is about the angle between the fins and the centerline”, is that the angle between the fins and the center line is the one that shapers use for measurement, and placment, but that angle is mostly irrelevant with regards to what is happening in the dynamic wave/board/surfer system. It is how the surfer manipulates the orinetation of planing surface that determines the orientation of the fins to the flow, and the manipulation is directly effected by the rail/rocker/bottom-contour curve.

P.S.

Discovering new (personal) understanding of a subject does not eliminate surprises. In fact, i would say that the best surprises are the ones you get when you discover the new understanding. It is a surprise because it is different than you originally thought. Furthermore, when you discover a new understanding, you always uncover new mysteries. In my opinion, leaving things to magical and mysterious is boring, the fun part is discovering the new surprises.

im not sure i understand the whole one curve thing...there are many curves that make up the rocker alone let alone the bottom and tail rocker along with the outline template...in my mind a curve or is part of a perfect circle...unless the whole bottom profile of a surboard continues on from the nose and tail to meet somewhere to from a perfect circle then there are different curves that make up the bottom...same with the outline...if you know snowboarding or skiing...a lot of the boards are coming out with dual radius sidecuts...where the curve of the effective edge is made out of one circle for the middle and another size circle closer to the nose and tail allowing better control on your edges...i dont think a surfboard would feel very comfortable or be as fast (dont want to start the speed thing up) if the middle part of the board wasnt a bigger circle than the smaller circles that make up the nose and tail...maybe im looking at this differently...

also about the angles...are you making a triangle between the nose, and either side of the tail?  kind of confused by this...if this is the case would you have more extreme angles on wider boards...again maybe im just seeing things differently

If you are not thinking in 3-D and want to think about each plane, or line separately then there are lots of curves. If you are thinking in 3-D then there is one curve, IMHO.

If you only define a curve as one with a constant radius (and that is not what is being discussed here), then you are breaking it down even further, but I don’t see the value of thinking in terms of curves with constant radius when thinking about board design, unless you are programming a computer. But that is just me.

well to me you would almost have to break it down...at least into 3 different curves...entry rocker...bottom...tail rocker...maybe well say 3 different arcs that make up one curve...ah...its the weekend

Aloha KC,

“KC : So how are you setting toe? In fact when you do this kind of adjustment, are you inclined to make any other adjustments”

I always toe my fins with a flexible straight edge in relation to the nose. Weather it be 1 1/2 off the nose(thrusters) or 4 in(on twins). I find this much more accurate then going off the stringer. With the rocker, template, bottom I use on a 7’6. 12 in. on the forward fins and 4 on the back work great. I can still ride the board from a forward position and not have to step way back to do a turn. I can’t remember exactly when I did the research on the fin settings but I can tell you that it envolved sanding off fins and replacing them many times.=)

Mahalo,

Mike

Run the edge all the way up the rail to the nose and the board becomes tracky.

interested if any of you guys have actually tried that. as it something i have done to see what happened. mostly i just followed the bottom edge line all the way to the nose and had a resin edge. not hard and square past the normal place but definitely an edge. the board picked up to planing speed quicker & felt looser overall having more release, albeit a little too much in committed full rail turns as it broke traction a little easier. the boards generally had more of a sensitive feedback to you. a presence of being feeling im finding hard to describe right now… i did a few for others and most were psyched our b4 riding them. those that did ride them felt no other untowardness than i did. no-one said they tracked. sorry Mike no disrepect intended. as i too like to learn from here, as well as give.

agreed... i wasnt clear on your definition of running an edge all the way up to the nose. when you say run the rail square all the way i agree with you. its a challenge at times to write what we feel so that others understand easily...

Maybe you misunderstood me or maybe I was unclear of what I meant. The example I was making was about the rail shape. Not the chine or little resin bead you make by running the tape up in the hot coat. Try making a board with a 90deg rail shape (like in the tail) past your front foot and see if the board tracks. Have you ever seen Ben Aipa’s bevel rails. They have edge but they don’t track. It’s because the bottom edge is still tucked under the apex of the rail.

Also the reason your boards felt like they got up on plane quicker is because water that breaks clean from the board has less drag. That’s why we have those nice sharp edges in the tail.

If you think that sharp/pinched/hard rails break traction sooner then I suggest you shape a board that has absolutly no edge in it at all. 50/50 all the way through the tail. Maybe you’ll understand what I mean then.

No disrespect taken by the way. Everyone has a diff. theory on what makes boards work.

Mahalo,

MW

G'day Mike, I too originally interpreted your comment on the edge to be a continuous hard edge like Dave Verall thought. In this case I have come across the idea that it can cause rails to catch (accidentally sink and dig) and i've seen a number of professional boards make an effort to make it extra rounded in the nose area, presumably for that reason. However some years ago Dave Verall posted something to the effect of that being a myth so I tested it and reported here on swaylocks. I made an epoxy version of my regular polyester ride and retained same rocker, outline (tailshape excepted) and hull contours so it was a good test.

[quote="\$1"]
i used masking tape to build up phenolic balloon bog on the rails which i sanded into a hard edge that runs the entire lenght of the board. This is Dave Verall rail theory. He posted his description here on swaylocks so i decided to test it
...
Dave Verall is correct! absolutely this board does not catch, the thicker rails throughout in fact mean it is less likely to sink a rail than my original.
...
i'm not entirely sure what the hard edge has gained me though, possibly a bit more skate speed, anyway like the original its hybrid rocker allows me to keep going when the wave turns to mush
[/quote]
http://www2.swaylocks.com/node/1009271

however if you meant "square rails" then i have made a board with squarish looking rails - what I did was no tuck throughout the board length - i was trying to get more hull planing area out of the outline shape. I did however round the underside corner off a little. The deckside of the rail was more rounded but still on the square side. This board did not track - it was a 5' 4" twin fin so I suppose something that short and squirrely is difficult to track. It was however awful and had a bad habit of accidentally sinking rails causing me to fall off (despite them being quite chunky). But maybe sinking a rail instead of turning is a form of tracking? Unfortunately I built that board in a stage of my life where I had to live with my mistakes for quite some time and I rode that board for well over a year. It did hone my surfing skills though!