Rotational Moment Chart

Long tenkara rods are notoriously tip heavy, that's just the way it is. It's very difficult to make a 4+ meter rod without having most of its mass away from you, and further away the center of mass, the more tip heavy the rod will feel. Physics can't be cheated. But some rods are less tip heavy than others. Why is this? Materials, design, and taper all play their roll. Is there a way to estimate how tip heavy a long rod will feel? Yes, it's called the rotational moment.

Brent Auger of DRAGONtail Tenkara winter fishing with a long tenkara rod. 


Just as a reminder, rotational moment is a mathematical tool used to estimate the tip heaviness of a rod. This measurement has been validated and is used by Gamakatsu, a high quality Japanese rod maker. I've written about Moment of Inertia and Swing Weight in the past, but these are harder to calculate, and since Gamakatsu has already accepted rotational moment as a measurement for their rods, I decided just to stick with it. The rotational moment of a rod is calculated by measuring its weight in kilograms and multiplying that by its center of gravity distance in centimeters from the butt of the rod, when the rod is fully extended. Any number over 6 and the rod begins to feel tip heavy, over 7 and you'll definitely notice. Simply put, the larger the number, the more tip heavy the rod will feel. Likewise, the larger the number the more stress on your forearm and more chance of micro-tears being induced in the extensor tendon with repeated use (think tennis elbow, ouch!). Moment of inertia is likely a better mathematical model, but it's also more complicated, so rotational moment (RM) makes sense to be the mathematical tool of choice. I published a detailed blog post about rotational moment. You can read it HERE

I have put together a chart of the rotational moment of tenkara rods (and one keiryu rod) so that these long rods can be compared. I will update the chart as needed. 

For the updated version of the chart, click HERE








No comments:

Post a Comment