Ideal kayak rod for big fish

Although I work in public relations now, at one time I was a jet aircraft mechanic and an engineering major. So I thought I would geek out for a moment to see if this would help. Changing your rod length will allow you to put more pressure on a fish, but to me it doesn't seem like that much more. I'll let you be the judge. 

I'll go into the math later, but by changing from a 7' rod with 10lbs of drag to a 5 1/2' rod you're only going to increase your drag capability to 12.7lbs with the same amount of pull/effort on the angler.

The picture below illustrates the physics of a fishing rod. The rod butt is the fulcrum, effort force (F_e) is where you hold the rod, load force (F_i) is your drag setting.
To calculate the effort required where you are holding the rod you use the following equation: F_e=(F_i*d_i)/d_e

For a 7' rod with a 10 lb drag setting and your hands 20" from the butt the force required is 41.9 lbs. In your intial post you mentioned that 10lbs of drag was about the max you could pull before your yak stability became a little too uncomfortable. So, lets assume that 41.9 lbs is the maximum amount of force you are comfortable with on your yak.
 
When you plug 41.9lbs of force (F_e) into the equation, reduce the rod length to 5.5' (d_i), and calculate the drag setting (F_i) you get 12.7lbs of drag.

I think on a large boat the rod lengths help alot because you can handle more force due to the ability to brace yourself against the gun whale, strap the rod into a fighting belt, use a fighting chair, or even use the rail to help you hold the rod up. In a yak we have none of those options. At some point there is a maximum amount of force we can handle before we lose the ability to keep our boat stable.

Rod action is going to help you deal with force and may allow you to take on extra force but when you translate that into drag setting you might gain only a pound or two of extra drag.
You've really got me thinking about this! I'm looking forward to reading your report on what you went with and what you were able to do on the water! 
But, I'll slightly modify my earlier statement to reflect the math. I don't think the rod is the limiting factor for drag setting, it's just one variable. I think what is going to limit your drag setting is the amount of force you can handle before your kayak becomes too unstable for comfort.

Now we're talking Jay.  If you noticed, my thoughts were changing 3 variables.

1) length of the rod.
2) position of the end of the rod from my hip to under my arm.
3) angle of rod from maybe 45 degrees up to 0-20 degrees down.

The angle of the rod changes the angle of the force load.  How does that affect the calculation of the force?

How does changing the position of the end of the rod change the force load at at the previous fixed position (the kayak and the rotational force needed to tip it stay constant)?

BTW, I'd be happy with gaining ~3 pounds of drag.  That means I step up from a 30# outfit to a 40# outfit.  It really is a big difference.

-Allen

So if you were able to increase the stability limit of the yak you would quickly increase the pressure you could apply to the rod there by allowing you to run higher drag.

The use of a sea anchor will make further calculation very difficult since the pressure the anchor exerts on the kayak will increase as the force moving the kayak horizontally increases. This is why the method would be very effective on a surface fish suck as a marlin and nearly useless on vertical fighting fish such as a halibut.

What about running tests with a diver pulling a line through different length rods at different angles with a sea anchor..... See how stable the boat feels.

The angle of the rod changes the angle of the force load.  How does that affect the calculation of the force?

The math above is slightly over simplified, but not so much as to make a significant difference since as you incorporate reality (the rod bends, the rod is held at an angle) the changes are proportional and the end result on drag is the same. Basically, the actual force numbers might be less, but they are related proportionally so the drag settings remain the same.

Also, as you increase the angle of the rod, you are transfering more force to the fishing line and the rod. That's why when you high stick you end up breaking your fishing rod, when you point the rod at the snag/fish the line peels out easier (you're also reducing pressure on the fish when you do this), and it's also one of the reasons we set our drag so far below the line's actual tensile strength (knot strength and wear & tear are others). I think if you're operating in the normal range of fishing, like keeping you're rod at less than 35 or 40 degrees (in a straigt line from butt to tip), then rod angle won't make much of a difference in the final drag setting. There are more complicated equations that could give us exact numbers, but it wouldn't be worth the work , and is far above my mathematical skills anymore.

How does changing the position of the end of the rod change the force load at at the previous fixed position (the kayak and the rotational force needed to tip it stay constant)?

Changing the position of the butt affects the length of the lever and the location where force is applied to the angler. If you tuck the rod butt under your arm pit instead of jamming the butt against your belly/seat, you reduce the working length of the rod and the distance of your hand from the fulcrum by a few inches.

IMHO I think you're on the right track with the idea that you have to change variables to reduce the force acting on the angler.

Allen,

Don't you have a really short Okuma rod sitting around somewhere?  Right around five feet, I'd guess.

Maybe you were on to something after all.

Happy holidays,

Paul

Allen,

Don't you have a really short Okuma rod sitting around somewhere?  Right around five feet, I'd guess.

Maybe you were on to something after all.

Happy holidays,

Paul

something tells me he's tossed that thing into a wood chipper and flipped it the bird as it went in!

i'm beginning to understand some of this BigFish talk now.....thanks fellas

+1.
Jim is taking his first long range trip in a month and built a nice stand up rod for 80+# line. He got advice from Mudhole and a number of guys who fish tuna each year. There's so much technical stuff like rod action, length, hardware, I was enthralled by it all. I can now see how traditional fiberglass would be a benefit in this application.

I've also been re-thinking roller guides.  Not sure they're needed in this application. 

Yeah, there was an article in WON about how the tuna sticks are all high powered standard guides these days, and rollers are becoming less common. I guess this has something to do with the changes in braided line?

Fascinating thread you guys cooked up, well done!

Oh come on Jay ... you can't get off that easy.  I want the torque equations!!!  I'm not concerned about the force I can put on the rod.  I'm concerned about the torque the kayak can take before rolling.

-Allen

Allen,

Don't you have a really short Okuma rod sitting around somewhere?  Right around five feet, I'd guess.

Maybe you were on to something after all.

Happy holidays,

Paul

something tells me he's tossed that thing into a wood chipper and flipped it the bird as it went in!

Still for sale.  If I don't sell it before April, I'm taking it back to Mex and seeing if I can't break it on another fish.

-Allen

I've also been re-thinking roller guides.  Not sure they're needed in this application. 

Yeah, there was an article in WON about how the tuna sticks are all high powered standard guides these days, and rollers are becoming less common. I guess this has something to do with the changes in braided line?

Rollers really come into play in a couple of areas.  A roller tip is good for when the angle of line coming out of the tip is very different than the angle of the line going into it.  Large angles create lots of friction.  Rollers reduce that.  A roller stripper addresses a similar problem.  It used to be you used these big coffee grinder reels for heavy duty fishing.  A large radius of the spool on these meant the line was some distance away from the rod, and the first guide (the stripper) had a larger angle on it.  With the smaller reels these days being just as powerful, the angle at the stripper is less.

The reason why I'm rethinking it is that I'm trying to reduce the angle at the tip anyway, getting as close to pointing the rod at the fish, but still be utilizing what a rod is good for (shock absorption being high on the list).  The angle of the line coming off the tip should not be too severe.

Roller tips have an issue that you need to hold the rod correctly to get the right action as the line needs to be laying on the roller.  Turn the rod and the line is no longer on the roller.  You don't have as much rod control on a kayak as you do on a bigger boat, so I want a little more flexibility.

-Allen

Handline and a saddlehorn.

I'm concerned about the torque the kayak can take before rolling.

There is no equation for that, it comes down to how bad-ass you are on a yak! 

I'm concerned about the torque the kayak can take before rolling.

There is no equation for that, it comes down to how bad-ass you are on a yak! 

I'm pretty sure it has nothing to do with that.  The torque you get from the rod is way beyond any normal torque you encounter when paddling.

Am I going to have to put on my physics hat now?   

-Allen

I'm concerned about the torque the kayak can take before rolling.

There is no equation for that, it comes down to how bad-ass you are on a yak! 

I'm pretty sure it has nothing to do with that.  The torque you get from the rod is way beyond any normal torque you encounter when paddling.

Am I going to have to put on my physics hat now?   

-Allen

If you can calculate the torque it takes to roll a kayak I would love to see it. Hull shape alone is way to big of a variable for me to try and assign a value to. Then you get to look at the length of the lever, the distance from the side of the boat, the center of gravity for a boat with a paddler. Whew! 

If you can calculate the torque it takes to roll a kayak I would love to see it. Hull shape alone is way to big of a variable for me to try and assign a value to. Then you get to look at the length of the lever, the distance from the side of the boat, the center of gravity for a boat with a paddler. Whew! 

I'm not interested in the absolute number so much as I'm interested in the difference in approaches.

I think one can make reasonable assumptions on most variables and come up with a valid comparison, much like you did with the comparison of 5' to 7'.

I would never have started down this road if you hadn't opened the door.  Gee, thanks!!!   

-Allen