alan tani @ alantani.com fishing reel repair rebuild tutorial The physics of fishing the rail
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October 22, 2019, 01:14:24 AM *
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Author Topic: The physics of fishing the rail  (Read 1384 times)
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boon
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« on: August 05, 2019, 02:10:05 PM »

I was doing some thinking (dangerous, I know) about the physics of fishing the other night, and I somehow got onto the topic of fishing the rail.

Using the rail completely switches up the physics of using a fishing rod. The traditional "stand-up" pivot point, being the gimbal, disappears, with the new fulcrum being the rail. This makes some interesting things happen around the lifting force or pull that is actually transmitted to the line.

Note this is all a massive over-simplification of things, and doesn't account for things like rod-bend - I suspect what actually happens stand-up is that a new dynamic point of pivoting is in effect, but it's hard to model.

So fishing the rail will always have one inherent limitation. You cannot push down on something, unless you brace against something above you. All you can do is exert a percentage of your body weight upon it, and then let gravity do the work. You can vary how much weight you put on it, but you physically cannot sustain a downward force greater than your own weight.

This said, the shift of the fulcrum in the system does some interesting things.

Let's work on the model of a 7ft rod, 20lb of drag over the rod tip.
Fishing this stand-up, let's say you're gripping (lifting) the rod 2ft from the gimbal. 20lb of drag at 7ft from the pivot (again, ignoring rod bend) is giving you 140ft/lb of twisting force at the gimbal. In order to oppose this, you need to exert 70lb of lift @ 2ft from the fulcrum. That's a lot of weight to lift in a sustained manner.

Take the same setup and drop it on the rail at the same point. Now the length of the lever the fish has is reduced from 7ft to 5ft, reducing the twisting force at the rail to 100ft/lb. Because you still have a 2ft lever on your side to work with, you only need to exert 50lb worth of force, however you've reversed the direction, so all you have to do is lean on the rod with 50lb of body weight.

So let's take an average-ish fisherman, which we'll say weighs 180lb.

As an absolute maximum, using the dimensions above, they can generate 360ft/lb at 2ft from the rail. However, this would mean they were literally off the ground, supported only by the rod. This gives you an absolute maximum of 72lb of pull at the rod-tip (again ignoring rod bend).

To achieve the same stand-up, you would have to lift 252lb - not inconceivable for a 180lb person, but difficult, and certainly not sustainable.

The long and short of this is that fishing the rail allows you to generate, and sustain, pressure on the fish that hugely exceeds what can be done stand-up. The only way to get equivalent pressure stand-up is by shortening the lever that the fish has to use against you, and this is why serious stand-up rods rarely exceed 6ft in length. This is probably also why the IGFA says that you're ineligible for a record if the rod touches the boat at any point; it allows you to pull REALLY hard on a fish without actually exerting much strength at all.

One thing to keep in mind is that this all goes to bits when you "take a knee" as I see quite a lot of fishermen do with the rail. At this point, you're using your back and abdominal muscles to transfer the force of gravity to the rod, and all the advantages go out the window.
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Newell Nut
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« Reply #1 on: August 05, 2019, 03:34:53 PM »

Well put and fishing the rail for reef fish is the way to go when the big one gets on. I hit the rail and crank with all I have to get the fish away from the sharp stuff before cutting me off. A lot of companies design rods and blanks just for rail fishing. I like the performance of my Seeker Hercules rods on the rail. Killed a lot of big fish and have not damaged a rod yet.

Dwight
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MarkT
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« Reply #2 on: August 05, 2019, 03:42:27 PM »

My 7.6" UC Viper and Invictus rail rods are great for fishing for cows like the one in my avatar.  It was the 1st fish I ever caught over 100# and it went 298.8#.  The rails on the long range fleet out of San Diego are fairly tall but I'm even taller and rail challenged without taking a knee. If you have to move down the rail to follow the fish it's a whole lot easier when you're not strapped into a harness.
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boon
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« Reply #3 on: August 05, 2019, 09:02:44 PM »

Well put and fishing the rail for reef fish is the way to go when the big one gets on. I hit the rail and crank with all I have to get the fish away from the sharp stuff before cutting me off. A lot of companies design rods and blanks just for rail fishing. I like the performance of my Seeker Hercules rods on the rail. Killed a lot of big fish and have not damaged a rod yet.

Dwight

If you can lift more than about half your body weight, you may in fact be better just leaning on the fish stand-up for at least the initial run. Chances are you can probably put more force on the fish in a hurry like that. Harder to crank on the fish that way though; depends if you're using the rod or the reel to try to turn the fish.

The maths is confusing me but I'm fairly sure that fishing the rail puts enormous forces on the rod as well; significantly more than stand-up for the equivalent amount of lift at the rod tip. Certainly the torque at the fulcrum is tremendous on a rail rod, whereas if you're stalemated stand-up there is no torque at the fulcrum.
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oc1
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« Reply #4 on: August 05, 2019, 10:23:00 PM »

Standing up and strapped in, the fulcrum is at the reel harness lugs.  When you pull on the fore grip at the same time the fulcrum moves up and will be somewhere between the harness lugs and your hand.  On the rail the fulcrum will be at the rail.  It is no coincidence at the stand-up fulcrum and the rail fulcrum are very close to each other.

Either stand-up or rail, you are pushing down with your weight at the gimbal.  The fish is pulling down at the rod tip (still ignoring the bend).

Foot-pounds at the rod tip is the distance (in feet) from the fulcrum to the tip multiplied by the pounds of pull.  The pounds of pull will be very close to the drag number pounds.  

Foot-pounds at the gimbal is the distance from the fulcrum to the gimbal multiplied by the amount of weight being used to hold the gimbal down.  

If the rod is on the rail and you are standing on a bathroom sale, your weight reading on the scale will be less than your actual weight.  The difference is the amount of weight being devoted to holding the gimbal down.

The foot-pounds above the fulcrum (at the rod tip) and the foot-pounds below the fulcrum (at the gimble) must be equal.  If they are not equal, you will either be catapulted or pulled over the rail, or you will fall over backward and snatch the fish out of the water.

So, if you know where the fulcrum is, you know the distance from the tip to the fulcrum, you know the distance from gimbal to the fulcrum, and you know the pounds of pull at the tip (about the drag number), then you can calculate the pounds needed to hold the gimbal down.  The pounds needed to hold the gimbal down cannot be more than you weigh.  In practice, it will be quite a bit less than you weigh because being suspended in the air by the rod butt would feel very freaky and scary.

If you go through the calculations with your current rod, then you will have all the information needed to predict the effect of a longer or shorter rod.

-steve
« Last Edit: August 05, 2019, 10:27:41 PM by oc1 » Logged
Cor
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« Reply #5 on: August 06, 2019, 12:14:30 AM »

Down here we only fish stand up tackle or sometimes using a harness for large Yellowfin tuna.   Because we cast lures at Tuna I very seldom fish anything shorter than 10ft6 in which is not ideal and not suitable for a harness!

The only time I've ever used a rail was when my arms were finished from pulling on a fish that was too strong for me, and I believe that the rod will break if it incurs any significant pressure against the rail so do my best to keep it away from there.   In fact I know it will probably break as I've seen it happen.   

I would suppose that Rail Rods are strengthened at the point where they come into contact with the rail?

As to the scientific stuff Huh? Huh?
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Cornelis
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« Reply #6 on: August 06, 2019, 12:36:15 AM »

Sorry for derailing the thread  Smiley, just a sideline question Cor, do you use high end spinners when throwing lures for tuna and what rods?
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Cor
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« Reply #7 on: August 06, 2019, 12:38:38 AM »

See PM
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Cornelis
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« Reply #8 on: August 06, 2019, 01:25:55 AM »

This is why I like my Seeker Hercules for the rail work when bottom fishing. The rod in the picture is a Hercules 40-80 just like I build for myself and many others over the years.


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RowdyW
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« Reply #9 on: August 06, 2019, 03:37:42 AM »

Dwight, in the photo the first guide is on the bottom. Doesn't that let the line rub on the rail? Either the reel is on the wrong side of the rod or the guides are started on the wrong side of the rod. Very confusing.Huh? I see that the rod is spiral wrapped.      Rudy
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« Reply #10 on: August 06, 2019, 05:01:15 AM »

Wow, that pic shows a surprisingly sharp bend at the fulcrum point.  Looks like it should break.   
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« Reply #11 on: August 06, 2019, 05:16:50 AM »

This is why I like my Seeker Hercules for the rail work when bottom fishing. The rod in the picture is a Hercules 40-80 just like I build for myself and many others over the years.





Impressive! If something snaps there though you may well be minus a few teeth!
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« Reply #12 on: August 06, 2019, 05:59:51 AM »

That is Billy Vivona a builder from New York. I normally fish about 22 lb of drag on my Newell 540 so mine has never bent that much when on the rail. The photo merely shows the power of the rod blank.

Dwight
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Cor
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« Reply #13 on: August 06, 2019, 06:46:02 AM »

Wow, never seen a rod like that!
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Cornelis
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« Reply #14 on: August 06, 2019, 03:15:18 PM »



Impressive! If something snaps there though you may well be minus a few teeth!
I just saw this, you make a good point Leon, his face is lined up just right Roll Eyes
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