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-   -   Swing weight question ? (http://www.theflyfishingforum.com/forums/fly-rods/318161-swing-weight-question.html)

fly_guy12955 05-01-2013 01:36 PM

Swing weight question ?
 
On swing weight...just to satisfy the cat here,,would over-sizing a reel...say a 4,5,6 instead of a 2,3,4,,,thus adding slightly more weight,,add or subtract from swing weight of the rod ?

Physics elude me to no end. I know this is just simple stuff to someone else.

Michael

silver creek 05-01-2013 03:10 PM

Re: Swing weight question ?
 
There is the elusive property of rod/reel balance and then there is swing weight. They are not the same.

Swing weight is both the difficulty in getting the rod to move/swing and the difficulty in getting the rod to stop moving/swinging. It is NOT decreased by getting a heavier reel. Actually swing weight is increased with a heavier reel because now you have the heavier reel that you need to both start and stop moving.

Swing weight is a combination of the total mass of the rod and the distribution of the mass. Greater mass toward the tip end of the fly rod increases swing weight because the end of the fly rod has to move faster, and the increased velocity increases the energy to both get the object moving to that velocity and to stop the object from from that velocity.

In practical terms, swing weight is how tip light or heavy the fly rod is. The ultimate fly rod/reel combo would have no mass. We would only be dealing with the mass of the moving fly line when we cast. We could stop the rod and start the rod much more easily and we could hold the tip of the rod up for nymphing more easily.

We now have 10 and 11 ft single handed fly rods because of the lighter and stronger modern graphites and resins that allow the production of low mass rods that keep the swing weight down to a level where we can comfortably fish them.

Think of swing weight this way. Think of a 4 lb bag of sugar. Think of hanging it off of your belt and spinning in a circle and having then to come to a complete stop. Now think of holding that 4 lb bag of sugar at the end of your arm with your arm extended and spin and stop at the same rate. You could not do it because with the bag of sugar extended, the angular momentum or torque required to start and stop it is much greater with the mass further from the center of rotation.

A fly rod that is casting also has a center of rotation and the further the mass along that fly rod is away from the center of rotation, the greater the "swing weight" or angular momentum.

fredaevans 05-01-2013 04:59 PM

Re: Swing weight question ?
 
Read Silver's explanation and my eyes glazed over for a second. But he's dead on right. Only personal observation I could add is I like to slightly 'over reel' fly rods so they move slighly 'tip high' on the swing. Much easier on the wrist/arm/should over a long days fishing.

aggieoutlaw 05-02-2013 09:10 AM

Re: Swing weight question ?
 
Fly Guy,
Silver Creek has offered some sound advice here. He is describing the mechanics of rotating masses. When you think about the motion of casting, it is largely a rotation about some pivot point (your hand).

You can think of the rod as a beam with a tapered mass distribution and the reel as a counterweight. Every rod/reel combo has a balance point, the center of mass. Ideally, you want that point to be somewhere near the grip so that the rod comfortably rotates about your hand (it depends on your casting stroke, but I prefer a balance about my 1st and 2nd finger). If the rod has too heavy a reel, the balance point will be too "low", a light reel vice versa.

Balance and swing weight are different. However, both are important to comfortably casting all day. If the rod is not balanced, your hand/wrist/arm muscles must compensate by torquing the rod to rotate. Swing weight has more to do with how much mass is located away from the balance point (center of mass). This property is called the "moment of inertia" in physics/mechanics.

Think of a barbell. It has a center of mass in the middle of the handle (where you grab it). A barbell is very difficult to "twist" because of there is a lot of mass away from the center of mass. The further the mass distribution away from the center of mass, the worse (much worse actually) this problem becomes. The whole time you are trying to rotate ('twist') the barbell, it is balanced about your hand.

Now think of your rod. You want it to be balanced so that it comfortably rotates about your hand. You also want it acceptably light so that the swing weight (moment of inertia) is not too tiring after hours of casting. You'll here the terms tip heavy or tip light. Sometimes these are used to describe the mass distribution, sometimes these are used in an inconsistent manner and can lead to confusion.

Perfect example: I have two 2wt rods. Both are exactly the same weight and length. However, one rod is lighter in the tip and heavier in the butt. This rod requires a lighter reel to balance. The rod/reel is therefore lighter in general. Because of this, the rod has a lower moment of inertia and a much lower swing weight. It is vastly easier and more comfortable to cast.

The heavier tip rod needs a (slightly) more massive reel to balance properly. However, if I simply added an even heavier reel to make the tip feel lighter, all I've really done is shifted the balance of the rod lower (toward the reel). But inherently, I've worsened the situation. Now the tip mass is even further from the balance point which is now uncomfortably low. And the more massive reel is acting as a more massive counterbalance and is also causing me to apply more torque to the system, and that torque is not being applied about the center of mass because I'm not gripping the balance point. I'm turning the system into a barbell...a barbell that I'm not gripping in the middle.

In short, a more massive reel doesn't help. The mass distribution (think taper) of the rod will ultimately determine it's swing weight. You should balance the rod with the lightest reel that will put the center of mass in the comfort of your casting hand. Longer rods will inherently have higher moments of inertia and require more massive reels to balance. That's why it's important to get a light tipped long rod for comfortable casting.

Hope my thoughts help.

silver creek 05-02-2013 03:07 PM

Re: Swing weight question ?
 
Swing weight is the reason that two handed rods exists. When a fly rod gets longer and has more mass than we can handle with one hand, we need two hands to rotate and move the fly rod through the casting stroke. Said another way, two hands are required when the swing weight of the rod is greater than we can cast with a one handed technique.

mrfzx 05-03-2013 01:38 PM

Re: Swing weight question ?
 
You guys are making my heart flutter! My two passions come together as one: Fly Fishing and Physics!:thumbsup:


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