I just read somewhere that rocker was voted the most important design factor in a surfboard somewhere. Why?
Can someone please calculate the radius a 6’ thruster with 2 1/2" of tail rocker describe(similar to the sidecut radius of a snowboard. I’m way too lazy right now)… Now compare that to the turning radius of said 6’ thruster. I would (wild guess) that they don’t quite match.
So why is rocker supposedly so important?
regards,
Håvard
It dictates flow,stabilities and turning abilities.++++Herb
It was once explained to me as this…guy likes getting Eatons shaped…he had a magic board, wanted Eaton to duplicate it. Eaton was in SoCal, surfer in SF, several hundred miles apart.
First, he took a masonite template and sent it to Eaton. Eaton made a board with that template. Board did not have magic.
Then, he took copious thickness foil measurements, and sent those to Eaton, next board still sucked.
Next, SF surfer built a jig to measure the rocker carefully. Sent the entire jig to Eaton to make sure the rocker could be duplicated.
Magic board…
That surfer went on to write Essential Surfing.
Boards with bad rocker are just unworkable…I had a gun made that was 8 ft long with 2 inches of tail rocker, and it totally sucked. 2.75 to 3 inches, and it works.
Bill Hickey and I discussed one of his 8 ft 1974 singlefin guns…he said I should not even ride it, rockers of the day were WAY too flat, and the board couldn’t come close to a modern rocker in performance.
As to WHY board performance is so sensitive to rocker, your guess is as good as mine. But miss the tail rocker by 0.25 inches, and the whole board is thrown off. Miss by 0.5 inch either way and it is a sure dud.
You can screw up boards with bad foil or planshape too, but it takes a bigger error.
Many shapers today do not grasp the full importance of rocker because pre-shaped blanks take all the guesswork out…
But go grab 100 different 6 ft thruster shortboards, and their tail rockers will all be ± 0.25 inches of each other. The tail widths will range over 4 inches, thickness over an inch. A good design STARTS with appropriate rocker.
As to WHY board performance is so sensitive to rocker, your guess is as good as mine.
I’ll take a guess…
‘Majic’ happens when the bottom curve best matches the wave’s curves and/or the rider’s style (you wouldnt want to drop in on a steep fast curvy face with a long flat board…or surf a slow phat musher with a banana rocker)
On a more technical note…yes rocker affects ‘flow’, which in large part relates to pressure/drag affects. I think entry rocker is way under-rated.
I also think rocker has a lot to do with fitting into the pocket, especially on smaller, hollower waves. I’ve got a small, flat, curvy “modern fish” that just won’t ride in the tube like a normal thruster because it lacks that ability to “fit” into the steep curve of the barrel. It has a tendency to catch a nose rail in the tube…
Since noseriders are what I know, that’s what I can comment on.
Most people have a preferred length, favorite size, typical go-to board in mind. It comes from a combination of your size, your experience, and the waves you’ll surf with it. Mine happens to be around 10’0". Most any 10’0", give or take a couple inches, will work just fine for me. Thickness, widths, weight, fins…they all work. The size is just a good fit.
But rocker…if that 10’0" has bad rocker, its a deal-breaker. Won’t paddle, won’t noseride, won’t cutback, won’t plane while knee-paddling…I always know right away. Shapers whose rocker needs work make that 10’0" into a 10’4" or a 10’6", using extra foam to make up for the flow inadequacies. It kind of works, but creates other problems (cumbersome) as well.
And good rocker, even ‘perfect’ rocker? Goes the other way. I’ve had a couple, and used a few more, boards that felt just right in every way and were only 9’6" to 9’8". Sitting on it in the water, they sink more than I’m used to; they feel too small standing there with them under my arm. But give it a couple strokes or get up & into a wave, and all the questions evaporate. Magic, as they say.
So I guess good rocker lets you be comfortable with a smaller board than ‘normal’, while bad rocker requires a larger board than normal to make up for it.
Here’s a calculation (picture attached):
L = length of board
R = radius of curvature of bottom
r = rocker (here defined as the distance from a line drawn from tip to tip to a parallel line tangent to the curve of the bottom)
Here’s a corny picture:
A little geometry (A^2 +B^2 = C^2) says:
(L/2)^2 + (R-r)^2 = R^2
Expanded and simplified we get the general expression:
R = L^2/4/r
-More rocker or shorter length reduces the radius
-Less rocker or greater length increases teh radius
Working in inches with the board you described :
R= 72^2/4/2.5 = 518.4" = 43ft
Of course this doesn’t account at all for flex during turning and will reduce R even further as curve bends into the turning board: a much harder problem.
Matt
Try riding it higher in the pocket,justa suggestion.
Width will kill it quicker in a tight steep pocket.
i was thinking about rocker today at work.
funny this thread should be here when i got home.
so, i have a question for all of you with more shaping
experience than me (pretty much everybody on Sways).
instead of just measuring nose and tail rocker, wouldn’t it be better
to lay a surfboard bottom up on a table that is level, lay a
really long level on the bottom of the board and just measure
where the apex is? your nose and tail measurements would
be the same and you would give the apex location. for instance
instead of saying 5 inches nose rocker and 2 inches of tail rocker
you would say 3.5 inches of rocker, apex 3 inches behind center.
it seems like this would give more info on the actual character of
the rocker of a given board.
Hi Haavard,
Wasn’t there a thread a while ago about a guy that had two boards that were very similar except for rocker? He noticed that the one with a greater nose rocker paddled better and it confused him. So he did some experiments including how many strokes it took him to cover a distance comparing both boards and sure enough the one with more rocker paddled better. Strange indeed. Its somewhere in the archives.
Anyhoo, I agree that rocker is essential though, because hotwiring my own blanks now just shows how much of a hack I am. This made me realize that whatever board you’re riding whether it be poly, epoxy, xtr, or compsand if your rockers suck might as well be riding a concrete slab.
Cheers,
Rio
I do kinda the same thing when I measure rocker. I put the board bottom up, find the apex with a level, and measure the distance from midpoint. then I take a rocker measurement every foot until the rocker starts to accelerate, where I begin to measure ever 6 inches, then every 3. It gets me close enough.
I do the same thing for planshape, then I connect the dots with a long, flexible stick.
IMO rocker, like any design component, is over rated as a single entity.
Unless it “fits” the outline curve, bottom contours, rail contours, thickness foil and fin design/placement, any individual rocker design considered on it’s own is practically meaningless.
On the other hand, many different rockers will work just fine if they are combined with all the other parameters in a well designed board ridden by the rider and in the waves for which it was designed.
i was thinking about rocker today at work.
funny this thread should be here when i got home.
so, i have a question for all of you with more shaping
experience than me (pretty much everybody on Sways).
instead of just measuring nose and tail rocker, wouldn’t it be better
to lay a surfboard bottom up on a table that is level, lay a
really long level on the bottom of the board and just measure
where the apex is? your nose and tail measurements would
be the same and you would give the apex location. for instance
instead of saying 5 inches nose rocker and 2 inches of tail rocker
you would say 3.5 inches of rocker, apex 3 inches behind center.
it seems like this would give more info on the actual character of
the rocker of a given board.
That’s exactly what I always do . .
Hey ChrisP, if you have a few hours to kill, look up “Rocker Apex” in the archives. enjoy.
Yup.
Rocker is important. However it is the comnbination of the other physical aspects of a particular board (rails, foil, fins. etc, ect, ect,) that all combine to deliver a boards turning radius.
I think we all collectively agreed on that a long time ago.
But here’s a new wrinkle.
You also need to throw in riding style into the mix. A power surfer will generate more flex thus altering rocker as compared to the same board ridden by a surfer who flows more. More flex = tighter radius.
The snowboard analogy doesn’t really work to well becasue there are so many other factors invilved in the turning radius of a surfboard as campared to the sidecut radius of a snowboard. It’s the sidecut radius on a snowboard that is the largest determing factoir in turning radius. But for the reasons above there are too many variables to really determine a true representation of a surboards turning radius.
Drew
thanks Ted. will do
Well…
The way rocker is measured in a static inches figure seems way off, since the overall angle of it from the rocker apex or the curve(s) and semi-flats, and the length of the rocker anyway is/are more important. If you had 1.5 inches of tail rocker on a 8’ board with the WP 4" forward, or 1.5" of tail rocker over a length of 4’4", that’s a much different story than a 5’10" fish with a WP 3" forward of center. And with major tail width differentials, huge variation in handling.
Vee or concave makes for several different rockers.
It’s all interconnected, like the water flow itself. That’s what makes the magic.
You also need to throw in riding style into the mix. A power surfer will generate more flex thus altering rocker as compared to the same board ridden by a surfer who flows more. More flex = tighter radius.
The snowboard analogy doesn’t really work to well becasue there are so many other factors invilved in the turning radius of a surfboard as campared to the sidecut radius of a snowboard. It’s the sidecut radius on a snowboard that is the largest determing factoir in turning radius. But for the reasons above there are too many variables to really determine a true representation of a surboards turning radius.
Drew
I like the snowboard anology because it flexes more than a surfboard and are pretty consistant in shapes, yet they are still not limited to the turning radius of the sidecut nor flex. And in deep powder the sidecut and flex both become irrelevant, there is nothing for the sidecut to grab onto and they are way too stiff to flex any relevant amount. They still turn.
I agree with the rest you pointed out though, except you need to throw in wave size, type and form into the equation too.
regards,
Håvard
"Try riding it higher in the pocket,justa suggestion.
Width will kill it quicker in a tight steep pocket"
Hi herb. Would you mind expanding on this thought. Sorry if I’m being dense. Width will kill what in a tight steep pocket and why? Thankyou for your knowledge.
hunta
In a tight, steep pocket,especially smaller waves ,speeds tend to be a bit zippy.A board that has more width with cause you more problems,and will require more effort than a narrower board of that similiar shape… in that same wave.
Flatter rockered boards can be sucsessfully ridden in steeper, sucked out waves,as long as you don’t go to the bottom.That’s where the board will pearl,or bog down.If you keep it up,higher in the wave, not traveling to the bottom,you can get away with alot more.