Rocker apex?

Ok, i’ve read many posts about wide point, but what about rocker apex, where would you want it on a short board? A fun board and a longboard? I know on my modern fishes I have put it 6-8" back of center with good result. Any comments?

Rocker apex is poorly defined. Surfboard rocker curvature is least in the central portion of the board, and max closer to the ends. Rockers are thus defined as perpendicular deviation from a line tangent to the stringer at the mid-point.

I took a whole bunch of measures of rockers and tried to fit them mathematically - it takes a third order polynomial to do it reasonably well, mainly because the increase in curvature at the transitions from center to rear is usually sharp.

“Rockers are thus defined as perpendicular deviation from a line tangent to the stringer at the mid-point”

exactly! a concise definition that describes the entire bottom of the board and is reproducable. I just can’t grasp the “rocker apex” concept.

Hey Daved. If I’m hearing you right, maybe what you mean is the '“peak” of the rocker, which is not necessarily the same as the apex. This subject gives me a headache, because I don’t know how you can consistently compare rockers without always measuring from the same point, like the center. When guys talk about drawing out their nose rocker and having it peak somewhere past the center, to me all that means is that they have a lower entry rocker and an accelerated tail rocker. This is what I would see if I laid my straight edge on the mid-point.

The only other way I can make sense of this is if you’re measuring the bottom rocker in relation to the deck, with the deck sitting level.

Can anyone explain this? I feel like I’m not understanding the most important aspect of board design. For the sake of theory, let’s assume a flat bottomed board.

a lot of rocker discussion occured in the Rich Harbor process video thread recently. But the short of it is you need some common reference point. If you want lower entry rocker (rocker ballance point behind center) you can still measure this from center. You may need to measure at smaller steps to reflect the rate of change.

Bottom line is it is all relative.

The question is what to make it relative too.

Board center is the common place.

I’ve thought alot about this subject and have come to the conclusion that the easiest way to find it is to place your board on your stands as though you’re surfing it in trim position, stand back and sight the lowest point. After all, the apex is really about where the board is wrt to your feet when you’re surfing.

I guess tho, this ain’t the most repeatable method - but I haven’t heard a better one! (that’s a lie actually Blakestah fits a polynomial curve - phew…)

Wow! I think I actually understand blakestah, but I had to read it 3 times for it to sink in. I am not a mathematician but would consider myself more of a right brainer with a really good eye. I can find your wobbles in you outline and the mistakes the unskilled finish sanders make on the perfectly symmetrical computer shaped board. I define apex as the highest point in a curve, but I am definitely not at the apex of my shaping abilities.

That highlights the problem with apex. Changing nose flip just a little can shift the apex quite a lot. But it hardly changes the ride of the surfboard at all.

The board is closest to flat in the middle. Choosing a line tangent to the stringerline, at the middle, gives a reasonably consistent reference.

…I define apex as the highest point in a curve

Yes, but how you orient the curve causes that point to move.

i.e. lay your board upside down on the floor and pick the highest point.

Now lift the tail till the flattest part of the rockers parallels the floor and you apex has moved basically to the center (or where ever your board is flattest).

Great responses to all, you have caused me to really use my mellon and with some of the response that was a task; but that was good thing, I did learn a few things.

I was gonna skip this one…

Its not about apex, its about transition…from entry rocker to transition to exit rocker. Shortboards are easier to see/understand because you stand at the same spot…the entry rocker fades between the rider’s feet in a relatively flat section…this flatter section will extend to just ahead of the front fins…this is a board pitch/trim pivot point and hopefully also a sweet planeing area. A typical shortie’s entry transitions about 10 inches behind center, ie, between the rider’s feet…this would be the “apex” IMO but I dont like that description.

Looking at the side of a board (deck side up) from about 10-20ft away is a very easy way to find it.

I also take a suplementary rocker sight/measurement with my rocker stick one foot back from the center of the board to better see the transition/sweetspot rocker…should be no more than 3/16 on either side of this (one foot away) for what I ride…whatever works. Confused yet?