What’s the generally accepted method for finding its position ( I put mine on the stands right way up so it looks as though it’s in trim and just sight the lowest point)
JC in 101 says “bigger waves, rocker further forward; smaller waves rocker further back” but G loehr says “hollow waves further back, mushy waves further forward” - who’s right?
How far behind (or ahead of) centre do you put yours and why?
What are the disadvantages of apex further back (drag?)?
Okay…I’m confused…happens more often than I care to admit!
When we measure rocker, we lay the board down on a flat surface, bottom down, so the the mid-point of the board is touching…then measure the distance between surface and nose or tail. Correct? This is how it has been explainded to me anyway.
How do we measure where the apex is? Is the apex not at the mid-point given how we measure rocker?
My understanding of how to measure rocker is this:
Put your board on the stands, deck facing the ground. Take a long straight object (must be as long as the board anyway) and set it at the center point on the board. Now measure the distance from the nose of your board, vertically, up to your “long straight object”…This would give you your nose rocker. Do the same for the tail.
Yes i know how to measure rocker, but where is the apex - and how is it measured. Lots of whimsical stuff but does anyone have anything concrete to offer?
I assume the apex would be that point on the bottom of the board from which tail and nose rocker are equal. Roughly, lay the board on the floor deck down and the place where the bottom of the board is highest is the apex…???
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How do we measure where the apex is? Is the apex not at the mid-point given how we measure rocker?
The ‘apex’ is just that. It is where the curve of the rocker changes direction - a ‘peak’. Usually it is very subtle (more of a transition curve than a real peak to the naked eye)but to find it, put your board fins up on a level stand with a light on it and put a black sheet behind it - you should be able to see the transition curve by eye with that sort of contrast. Or you can make level racks and set your board on them so that the ‘flat spot’ near the middle of the board (usually) is level, put a rocker stick with a bubble on the rocker stick’s center of gravity and the bubble will tell you where the apex is, but it will just confirm what you can see with your eyes… If the board has V or concaves, the stringer rocker apex can be at a different place than the rail rocker apex. If you are designing in CAD or drawing out a rocker template, you can place the curve how ever you want. If you are mowing foam, you can shift your template up or down on the blank and make marks to start planning from to put you rocker curve in.
SB, I have an 8’ piece of aluminum angle that is 2" x 2" that I use to measure rocker with. I have a mark at the 4’ (center). When shaping, I place the board on the racks deck down and the 4’ mark at the centerline then measure at the usual waypoints. I ususally put the rocker apex at the widepoint on my outline for baseline shapes. The 6’4" I just shaped had the widepoint and rocker apex @ 5T or 5" tailward of center. Since most rocker is a nice smooth curve it is hard to say where the apex is. I create the apex as a reference point and log the dimensions from there. Finding the apex on someone elses shape might be difficult. Rusty puts the rocker code on the stringer. you can get the apex there by moving the angle aluminum back and forth until it sits level at those refernce points. the variable will be what is level to an upside down board! Might be bad design to put the “theoretical” apex at the wide point but I have had good results so far. Good question! I would be curious to know some of the more experienced shapers theories on it! Bert??? I might actually get to try my new board tomorrow!
The shaping 101 video tells you to place the apex about 10" back from center.
Thats for a standard shortboard that will be ridden off the tail. Thus, this represents an apex that is roughly the mid-point between your feet. Makes sense when you think about controlling speed and board pitch. The apex or transition is a pivot point of board pitch. If you ride a board exactly in the center then your transition should be near or at center.
“Apex” is a very strong description…the transition between the entry rocker and the exit rocker is very very subtle on many if not most boards. You can identify the location by holding the board low in front of you laterally, both hands on one rail, arms stretched out, bottom side up. Keep looking and you’ll find it. Go to a shop with lots of respectable boards and look at them carefully. Most shortboards are pretty much the same…about 10 inches back.
When measuring rocker at the center, it is recommended that the stick you use is straight, balanced, level and tangent to that center point. I usually have to tilt the blank a little to achieve that (the center should be very close to horizontal level). By balanced I mean take your stick and mark the center of mass by balancing it on a pencil or finger. Then use that balance mark on your board center every time you measure rocker. You can check your accuracy of meas by repeating measurements often.
There is only one apex on a regular curve between two given points. That would be the tangent point your straight edge (rocker stick) forms when it is set, so that nose and tail tip are at equal depth relative to your rocker stick. The true apex can never be 10 in rear of center unless you are running greater tail rocker than nose rocker.
In my opinion you are wasting a lot of energy worying about the “apex”. Just take your rocker measurements relative to your rocker stick held tangent to the center point of your board. If you do this consistently with all your shapes, at least every 6in (3 is better, especially for short bords) you will be defining your curves in a consistent fashion that will enable you to tweak it hear or there, and figure out what works best.
You can still hold a straight line tangent to other areas on the stringer to see what the curve is clearly doing, but always try and correlate what you want to change back to the “tangent at center” method for consistency.
By the way, it doesn’t really matter to level anything when doing this. A tangent is a tangent regardless. I will shift my blank back or forth on the racks, so that I can achieve my tangent, and/or slide the rocker stick back or forth so it will balance tangent to center.
I’ve been biting my tongue wanting to say the same thing…how could the rocker apex possibly be behind center? it seems like such a board would have be paddled with your head hanging out over the nose! I don’t recall the Carper video even mentioning rocker apex…I think he suggests thick point being slightly behind center…besides apex seems like a nebulous concept…the rocker to be concerned about is the entire continuously changing curve flow from tip to tail.
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There is only one apex on a regular curve between two given points. That would be the tangent point your straight edge (rocker stick) forms when it is set, so that nose and tail tip are at equal depth relative to your rocker stick. The true apex can never be 10 in rear of center unless you are running greater tail rocker than nose rocker.
Every board with any rocker at all has an apex. If the rocker is smooth and continuous, then the apex is at midpoint. Having never ridden one, I really don’t know how such a board would ride but i suspect pretty miserably.
Measuring the apex using centre as a reference makes sense to me, but where is the balancing apex of a board when you reach the apex of a turn on any given wave? Can it be measured?
Say that is the rocker of a board laid flat on the racks, I know it looks extreme but it helps show the apex. The apex is the point that is touching the blue line marked 0. I think the best way to find to find the apex is to place the board in the racks and balance a long rod so that the rod is parallel to the ground. Where the rod touches the board is where the apex is. In theory this should be a single point unless you rocker has a flat spot.
I’ve got my own theory on rocker apex. You can’t accurately measure where it is without knowing either the nose or tail rocker dimension. For example, if you know the nose rocker dimension, you would place the straight edge that distance from the nose, and then see where the straight edge touches the board. That’s your apex. You can’t just put the nose and tail rocker the same distance because that doesn’t tell you anything about how the apex will work with where you place you feet on the board, and how the board will ride. For example, lets say you have 5" nose rocker and 1.5" tail rocker. If you place the straight edge the same distance from the board on both ends, you are moving the apex forward of midpoint, and obviousely that’s not right.
Here’s a good link that shows several different types of rocker with different apex positions and where they are in relation to midpoint:
Where the curve touches the baseline is where the apex is. You can see that they have one rocker that has the apex way back behind the midpoint, almost half way between the position of the feet. This would seem to be a loose board.
Lots of opinions here…there are even some doubting Carper’s who has probably shaped 40,000+ boards.
Gentlemen, forget about “apex”. The real quest is the transition between entry and exit rocker and it is all dependent on the pitch of the board when riding in the sweet spot that maximizes speed (forget paddling…too many floatation variables). This transition may be very short (pipe semi-gun) or could be long (classic fish). There are an infinite number of tangent points along a curve (a lot like Calculus). So the question is where is the ideal tangent measurement? The answer may be nebulous to some…Im going with what I know and what I’ve seen and I think JC would agree.
Think board pitch and planning speed as it relates to entry/exit rocker and the standard goal of achieving speed. Beyond the basics it quickly becomes pseudo-science. Read Greg Loehr’s theory of pitch and think.
Measuring rocker in the center is simply a widely accepted standard THAT WORKS. If youre real picky about measuring rocker then find a method that repeatibly gives you accurate results. One could measure 5 nose and 2 tail and another could get 4 nose and 3 tail. Infinite tangent points. If youre making a std shortboard and think the “apex” is at center then go right ahead, put it there and try it. You’ll go back to the standards later.
