Rocker question regarding "longer" shortboards ( 7' )

I have noticed that longer shortboard blanks have more rocker than their shorter cousins. This might be a stupid question, but, is that because on a longer board, more rocker is needed because its over a longer length??. I ask because i am tossing up between a shorter, wider flatter thruster ( 6’5’’ x20 ), and a longer thruster ( 7’ x 21 ), but on the longer blank, the lowest rockers i can get are 6.1" nose rocker, and 2.5’’ tail rocker, and im not sure if thats too much for the average waves we get around here. Hope this post makes sense, i have drawn the 2 on graph paper, and i like the look of the 7’er, and i’ve always liked mig length boards.

Cheers

Think curvature in addition to length and end numbers, and you can see some relationships.

The rocker of a shortboard will ride the same wave as the 7 foot board, so what rocker

will the longer board have? The board could have any rocker (not being a smart arse).

(so this may at first seem like a non-sequitur argument)

(but this is where the ‘art’ comes from)

If the 7 foot board is going to do the same radius turns only, then the rocker curve might need

to be the same as the 6 footer.

If the curve is exactly the same there will be too much water contact with the hull on the

longer board. This would be especially evident when the board is running in the flats or is

being paddled. So less rocker curvature than the 6 footer is needed just to function in the

same waves.

Less rocker in the 7 footer will not allow the same turns as the 6 footer, given the same

force/rider. So more rocker (end numbers) will be needed in the 7 footer.

Thus two otherwise similar boards of different length will have similar properties when the

rocker of the baseline board is used between absolute end rockers and rocker curvature of

the baseline board and are applied to the goal board. (try to wrap your head around that one)

The exact numbers have pretty much been figured, but the algorithm for finding them has

been “a lot of shapers figuring things out by trial-and-error”. Shapers watch what each other

do, right up to the top guys. The best shapers always seem to be aware.

In modern shaping the blank pretty much dictates what is getting made, so you are already

being narrowed in your choices. If you order custom rockers, then good for you, but you may

be turning your back on decades of developement. Full length permanent rocker gauges are

a big help in the learning process.

Get on a board about the right size and shape and ask yourself the critical questions what

that specific board needs, (ie. ‘more rocker, or less rocker, contour, rails, etc.’) then effect

the changes. Then iterate.

HTH,

George

There may be a good reason why many boards (short and long) are right about 14" (+/-) tail width and 2 1/3" - 3" tail rocker. A variety of other factors come in to play but that seems to be a fairly constant range in general purpose boards.

In actual riding conditions, most boards are ridden pretty much off the tail. I’ve seen pics of guys riding long and short boards with the noses snapped clear off. With that in mind, it makes sense that there is that general range of width and rocker to the rear 1/3 of so many boards.

A traditional fish shape is sometimes cut from a longer blank to flatten out the nose rocker and gain some thckness but some find that the standard “fish” blanks serve them well.

Hey Beerfan

Check out Midgets blanks at www.surfblanksaustralia.com

He has a whole range of 7’1" shortboard blanks starting at just over 5" nose rocker

You could even use one of his 7’0" longboard blanks.

They start at just over 4"

Cheers

Mark, MDS is right about Surfblanks Australia. Midget has several blanks that would be appropriate for a low or moderate entry rocker 7’ 0" shortboard. You can choose from “shortboard” and “mini mal” blanks. We’ve been using Midget’s Surfblanks Australia in Santa Cruz for several years (since Clark Foam closed in 2005.) Little did we know at the time that it was a significant step up in quality.

PlusOneShaper makes some really good points about the significance of curves between the nose and tail numbers. Curvature, as he refers to it, is arguably more important to your design than the numbers in nose and tail. If low or moderate entry is important to you, you’ll want a moderate continuous rocker throughout as opposed to flatter or staged rocker with a lot of lift in the nose.

Not to make too much of an assumption, but the “average” waves you’re riding probably have a combination of critical and soft sections. In such conditions a low or moderate entry with a clean continuous curve will offer good paddling and entry into waves, decent maneuverability in both the critical and softer sections, and the ability to glide or trim through the softer sections. Continuous rocker throughout the shape should permit you to surf the board from just about any place on the board - off the tail or further forward.

Here’s a profile for a 7’ 0" shortboard - low entry - continuous curve. It has 5.5" nose rocker x 2.75" tail rocker and is 2.89" thick.

Kind regards,

Steve Coletta

Beerfan - I remembered a similar discussion afew years back - G Loehr wrote this answer -

" Easy to do. Take any of your measurments on you 6 footer and scale them, lets do the nose rocker for instance. Let’s say the 6’er has 5 inches of nose rocker. You take the length of the 6 footer in inches, which is 72. Now you divide 5 inches of nose rocker by 72 and you get .06944444. Now multiply by the new length (7 foot) which is 84 inches and you come out to 5.83333. That’s your correctly scaled 7 foot nose rocker. All the other measurments can be done using the same method. " Greg says that rocker is thus directly proportional to your increased length. Now to decipher Plus One’s answer…

Thanks for all replies people. George, im a little stumped re your post, im not sure i get it ( i aint the sharpest tool in the shed ). Mick, i have the surfblanks catalogue, and the first one has 5.12’’ nose, but then has just under 3’’ tail rocker. Im just not sure if thats too low for our waves from knee to a bit OH. RE longboard blanks, I want to use a blank that’s as close as possible to the shape i want, as my last 2 boards have been made using knee board blanks. That was a huge pain in the arse, as they are so wide, that when you cut out your template, you take off so much width, the rails are crazy boxy. I dont want to do that agian!!. Nice shape cornelius, do you think the 3’’ of tail rocker would help in knee to head high beachies??

Just saw your post mate. So, generally speaking, a longer shortboard would have/could handle a little more rocker??

Thanks for that - been looking for some way of estimating how to stretch/shrink my rockers

In going through the example I found came out to:

new rocker at tip = new length" x old rocker at tip" / old length"

I think that the middle 1/3 rocker should not be changed much. It seems from looking at computer files that most shapers and lengths are running similar rocker through the middle 1/3 (in continuously curved rockers) - just the way it draws to the tip and tail differ. I like a bit of “bulb” in the curve from tail to middle 1/3, while other shapers prefer a flatter curve between the fins.

Hi Mark,

Yeah, I kinda figured I botched that one up pretty regular…

Basically, (exhale…)

(inhale, really big)

The 6 foot rocker has one curve, the 7 foot rocker will share some of this curve but will

be flatter. BUT the 7 foot board will not have the rocker so flat as to have the same

nose and tail numbers* of the 6 foot board.

*can’t just look at the nose equalling 5.2" and the tail = 2.6"

The proportion will be someplace close to what Greg Loehr said, but really the formula is

just a guide to get you in the right ball park. The actual curve will be the same “DNA” for

both boards. (Intuitive use of rocker templates for both boards will bear this out.)

For example, if you tail ride, you can have the same rocker in the last 24" for both boards.

Then the rest of the curve will be relaxed slightly in the longer board but still end up with

a higher nose rocker number, like 6.1" instead of 5.5"

Staged bottoms like this are a good approach, as are computer-generated proportionality.

(exhale, cough.)

That’s it. I’m spent. It is really difficult trying to explain a thing I do all the time, yet

there are so many idiosyncracies in the process. You got to just think a little and mostly

take a stab at it- you will learn something.

Just get a good looking blank and shape it…

Thanks george, that makes a lot of sense mate!, it’s great that people as experienced as yourself will take the time to help out noob’s like me. I think i’ll go with the longer board.

Beerfan, Greg’s formula for scaling rocker proportionately is a really solid idea. It certainly will provide a framework for nose and tail rocker and maintain the features of the curves throughout a longer board, which is arguably the most important part of scaling rocker. (The same can be said for scaling down.) Applied literally, when scaling up, I believe the formula results in too much rocker, particularly in the nose. Take a look at these numbers by example. The “coefficient” for scaling the rocker in a 6’ 2" to 7’ 0" (scaled length 84" divided by original length 72" equals coefficient 1.167) would be 1.167 multiplied by the nose and or tail rocker of the 6’ 2". A 6’ 2" with 5.13" nose rocker and 2.38" tail rocker would yield a 7’ 0" with 5.99" nose rocker and 2.79" tail rocker. That is a lot of nose rocker for a shortboard extended to 7’ 0". The tail rocker - 2.79" - is a little more reasonable over 7’ 0". Let’s take the formula a step further and scale the board from 6’ 2" to 8’ 0". The “coefficient” for scaling the rocker in a 6’ 2" to 8’ 0" (72" to 96") would be 1.33 multiplied by the nose and or tail rocker. That would yield an 8’ 0" board with 6.84" of nose rocker and 3.17" of tail rocker. Again that is a lot of nose rocker for for a shortboard extended to 8’ 0". And again, the tail rocker - 3.17" - is a little more reasonable.

It would be logical to say there’s a pattern developing using this coefficient to scale boards. It appears to yield moderately excessive nose rocker but reasonably accurate tail rocker. This is where our intuition needs to work with our observations and the “science of scaling.” I think it would be logical to add another “intuitive coefficient” to the process of scaling boards. Start with Greg’s formula to get an idea of how much rocker to add nose and tail, particularly because it will scale the rocker in the very important mid sections and entry (entry referring not to the nose but to the area of the board just aft of the nose where the bottom and rails generally initiate contact with water and wave) of the design. Then consider maintaining the scaled rocker in the tail, mid sections, and entry and drop the nose just enough so it won’t push water or air.

Fundamentally good surfboard design combines logic, deduction and intuition.

It shouldn’t be too hard to wrap our heads around those thoughts. Time for another deep breath - inhale - exhale ! Ahhhhh !!!

(This is using a slightly different mathematical equation / formula than Greg and Silverback’s formula, but it yields the same result.)

Kind regards,

Steve Coletta