On his excellent blog, Tom Davis posted a picture of an X-ray of the handle of an Oni rod. The X-ray appears to show some kind of insert near the butt. This sparked much speculation that the Oni rods are only so light in the hand because there is weight added to the butt of the handle to counterbalance the tip. I asked Tenkara no Oni directly if this was the case and he said no weight is added. I tried to share this on social media several times, yet people insisted there was added weight.
So, to finally put this question to rest, I decided to offer some better evidence. Here is a translation of what Tenkara no Oni has to say on the matter:
Hi Jason. I will answer the question . I have seen in the X-ray and added weigh?, are you saying , ( Part of the female screw) nut part of the end plug Desuyo . In mechanical terminology , it is not only this. All , it is made of aluminum . It ‘ll come with any Tenkara rod , at the tail plug As long as there is . Also pole of TenkaraUSA, Also Zerosum. In Tenkara nurses in Japan, anyone who has been found to the structure of the rod You know everyone . And to sell to fishing goods store . It is not anything in secret . You can see other pole also if you take X-ray . But , I think the person who was using the discovery of the disease is the good X-ray . In the photo , I went through parts of the nut part of the ass plug that is attached to the inside . It is a component different from that of during . Anymore , since causes a difficult understanding , I want you to stop , this kind of Ridiculous question .
To sum up, there is no added weight in an Oni rod. There is an insert to screw the end cap into but it’s made of aluminum (not the material of choice if you want to add weight to something). And, this type of design is common among other tenkara brands so there is no “cheating” by counterbalancing the rod.
Here are some pictures showing the insert in more detail.
Thanks for posting this article, Jason. I have since learned that adding weight to the rod handle does not change the Moment of the rod. Moment is a mathematical estimation of how tip heavy a rod feels. Adding weight may shift the balance point but it also ads weight to the rod. Moment (torque) is defined as the rods weight (in kg) times the balance point from the butt (in centimeters)m thus M=(kg)(cm). So again, adding weight to a rod handle does not change the Moment. I love my Oni rods and I’m happy that the myth has been busted!!
Thanks Tom. I have no idea what you just said but those sound like school words to me so it must be right. 😉
That would actually be an awesome compartment for an extra kebari or two.
Why is it that the only thing I remember is
‘Ass plug’?
Dave, perhaps an unfortunate combination of mistranslation and/or wishful thinking? LOL. (J/K).
I agree with Tenkara no Oni. The aluminum “butt cap insert” is a common piece of hardware on most of the tenkara rods I have come across. Hopefully our online instructions and photos will help shed some light on this mysterious piece of hardware.
LINK:http://nebula.wsimg.com/5be6ecb7dced04e3e51cc9e1dc649cea?AccessKeyId=E3010A400834EE328898&disposition=0&alloworigin=1
There are rods that do not use a butt cap insert, examples of these include the TUSA Iwana and TUSA Yamame (at least my 2-year old ones are like this.) The removable aluminum “butt cap” on these two rods screws directly into the graphite blank where threads have been machined into the blank.
Build your own tenkara rod and find out and see for yourself 🙂
First of all, I agree with you Jason that Tom’s answer must be correct since it sounds so scholarly. But I don’t get the original controversy. The rod handles like it handles; it weighs what it weighs. Would it really matter if he stuffed two chickens in there to make it handle so well? What’s the big deal?! JMHO.
…sounds like a lotta yada yada about nada… may i suggest we go fishing?… and don’t forget to bring an Oni…
I agree with Jim and Bob. What’s the deal? All this mathematical and philosophical discussion about the butt/weight whatever. Go to the river, enjoy it even if you don’t catch. Then spend time with family and/or friends. Please, I started Tenkara fishing because its simplicity and some of you are making all this noise. Do you have a life?
I think we are all forgetting why we fish with a tenkara rod….aloha
If I remember my statics – the moment of inertia at each point along the rod will be different. Based on the parallel axis theorem –> Moment of Inertia at any point = (Moment of Inertia at Center of Mass) + (distance from center of mass)^2 X (Mass). So your initial thoughts are correct. Added weight at the butt will change the center of mass and thus change the moment of inertia at all other points along the rod. The other thing you have to think about is not just the moment but the equilibrium forces at each point. Those forces will obviously change with added weight as well as holding position. The “tip-heaviness” when not moving the rod is really the result of the equilibrium force required to keep the rod balanced. When rotating the rod then there are going to be issues of angular momentum related to distribution of mass along the rod. It seems to me with the Oni rod that angular momentum is greater once I get it moving compared to other rods – once the cast is initiated the rod seems to want to want to keep moving.
As I revisited Tenkara Talk and happened onto this article, it reminded me of the counter-balance weights being added into the butts of longer rods, typically “flipping sticks” by competitive bass anglers. This practice started in the late 90s and early 2000s for a larger segment of the angling population. It may have been toyed with earlier but it really started to see its way into the world of competitive angling around those years in the U.S.A.
I’m not as well versed in the properties of physics which several of you have mentioned. However, I did use the weight systems in rods from 6′ to 7’6″ and I noticed an appreciable difference in the overall balance and way the rod rested in my hand. Varying the balance point closer to the rod hand, instead of the tip end, lead to less fatigue over several hours of angling, especially with the longest of rods, and the real bonus for me as an angler, came in the form of the rods overall sensitivity to fishing pickup up artificial baits, like assorted plastic worms and jigs. In some ways, its like the sensitivity differences between a stretchy nylon or copolymer line compared to a non-stretchy braided superlines.
Hi Jeffrey, thanks for revisiting! I remember those counterweights. Bass Pro used to sell them. While some tenkara rods are a little tip heavy, the ones I fish with aren’t (Oni, Tanuki, etc.) so I haven’t felt the need to balance them out yet. But I bet if you wanted to, you could probably find the right-sized washer at the hardware store.