This is an honest question in hopes of defining a “parabolic blank”. I am uncertain if the term refers to the “action” or the “power” of a blank or possibly both (and possibly other aspects as well). Through my eyes, the bending characteristics of ALL blanks are parabolic as different loads are applied to the tip.
A parabola can be viewed as an oval cut into quarters where the drawn line of the oval approaches "0" of the X-axis (say) quicker than it does on (say) the Y-axis. As more and more load is applied to the tip of a blank, the initial part of the bend occurs further into the butt section, but on a geometric scale rather than a linear scale. That equates to a parabola in my eyes.
Has the rod building / manufacturing industry borrowed (hijacked) the term “parabolic” from the world of math for use in a different manner as they did with borrowing (hijacking) the term “composite” from the composite industry? In the composite industry, the term “composite” simply refers to ANY and ALL Fiber Reinforced Plastic (FRP) structures (“laminates” to be more precise) whether containing a single fabric or numerous ones. In the rod building / manufacturing world, the term “composite” refers to a blank utilizing two or more fabrics, usually CF and FG.
In the end, I suppose a definite definition of “parabolic” as used in the rod building world needs to be established, recognized, and accepted. Once verified, then we can answer my original question “aren’t all blanks parabolic?” I am here to learn!!!

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

It refers to Action, and to very slow action blanks in particular. Even with a slight load on the blank tip, the initial flex is over the entire blank rather than just a shorter portion of it.

And yes, all blanks will flex into the butt if you apply enough load to them.

............

Tom,
Thank you for the reply. I certainly agree that “ Even with a slight load on the blank tip, the initial flex is over the entire blank rather than just a shorter portion of it.” To my way of thinking, that equates to all blanks being load-progressive or “parabolic”. I am hoping to learn if a proclaimed “parabolic blank” is any different from other “regular” blanks.

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

Mark, you're asking about the term "parabolic" as it's used in the context of traditional fishing rods and then trying to apply your understanding of the term "parabolic" to it. They are two separate and different definitions. You are coming close to the formal math definition of a parabola while in the fishing rod context it is a subjective description of action. I wouldn't call it "hi-jacking," I would call it a subjective fishing rod action description. Yes, less disciplined than the mathematical definition.

In the traditional fishing rod context it is as Tom said, a very slow action. They are different from most modern ( "regular?" ) rods since the trend for quite a while has been towards faster actions. And in my opinion, using the CCS Action Angle to describe the differences in action is valuable and accurate in describing the actions. Remember that old (from the 50's) glass Heddon spin rod of mine that we discussed? I think it can be called "parabolic" and its AA is 57.5 (Power ERN 5).

The closest thing to it that I have in graphite "regular" rods is AA=65. It is called "moderate fast" and "Inshore Popping." Most of my rods (except fly rods) are over 70, with some as high as 82. In the traditional use of "parabolic" to describe fishing rods, I think only the AA = 65 could be called "parabolic," and maybe not even that one.

If you watch fishing shows on TV notice that some of the rods used by the pros look "parabolic." Part of this is, I think, due to the fact that often they use slower actions that come close to "parabolic." Also, the use of "Go Pros" to record video distorts the appearance of the rods making them look more "parabolic."

Mark,
The perfect example of a parabolic rod is the shape that a pole vaulter shapes their vaulting pole as they fly over the high bars.

Note:
Observe the pole as it bends and then projects the jumper over the bar:

[www.youtube.com]

This is one of the reasons why fiberglass makes such great parabolic action or very slow action fishing poles.

If you want the design equations for the parabolic shape of your dreams, here are the equations:

[www.varsitytutors.com]

Best wishes



Edited 1 time(s). Last edit at 10/03/2021 11:53AM by roger wilson.

Thank you Michael and Roger for the information and definition. The fishing rod world uses the word “parabolic” in a different context than in math. Roger, I have always been intrigued if not dumbfounded how a pole-vaulter induces flex into the pole to propel them to such great heights; 20ft is truly remarkable!!! That is certainly a different definition of “high-sticking” lol.

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

Mark,
Of course I know the way that the fishing world refers to parabolic.

However, when one looks at a slow action rod that is loaded to its extreme - by and larger the shape described by the shape of the rod - is indeed a parabola.

The parabolas I am familiar with look like the letter "V" rounded off at the bottom - not at all like a fishing pole under tension?

Parabolas can be deep, or shallow. Old radar antennas are parabolic in shape. Examples of parabolic antennas, Old satellite dishes, radar dishes, parabolic reflators in solar heating applications. No fishing rod I've ever seen bends into a true parabola. Rather it starts flexing most deeply near the tip, and progressively less as it moves toward the butt. In fishing blank vernacular, a parabolic rod is simply a slow action rod.

Tight Lies and frisky fish

RJF