Science and fiction.

[gstours]

I've got a good question for some of you about lead weight dynamics in the presents of water flow.
   As a fisherman always trying and testing theory it seems to me that the shape of the weight can/could be altered to stay on the bottom hence a person might fish with less lead if this is possible.
The flat bottom is born at my house 🏠.  I've played with this theory for quite a while,  now I need experts to fill in the science part of my theory.   I've been wrong before,  and it's kinda hard to prove while you're fishing.   
Below are the two shapes in question.   Whenever possible if you anchoring and using bait the lead is just sitting on the sea floor.   Let's disregard the rocks and square edge argument as is very rare to stick it stuck.
  Thanks for your ideas and mathematics.🐙

[thorhammer]

Gary, I don't have one up here in the woods but long ago we started using flattened triangular weights with a hole through the middle flounder fishing, vs. egg sinker- low profile stayed on the bottom better Carolina rigging in modest current, and all types of surf fishing weights have flat sides similarly. Wheels roll, wheel chocks do not- go for it and I bet you reduce weight needed 20%. Always look forward to your R&D posts!

[gstours]

Thanks,  it seems like a flat bottom will have square edges and resist rolling or tipping more than the round cannonball that is most popular here.   We fish sandy, pebbles, mud mostly with bottom foliage.
  Some folks have shown me some rectangular lead sinkers usually 2-3 pounds they like more than cannonball weights.   
  Line diameter, depth, and bait size also comes here into the constant equation.

[JasonGotaProblem]

Ok so my experience using heavy weights of different shapes is limited, I'm more of a free liner or split shot kind of guy. However my experience considering the effect of different shapes on drag is a bit more extensive. So with that said I'll throw my hat in this ring.

Let's start with some basics. Fluid dynamics in water is very similar to fluid dynamics in air. The difference of course is that water is denser than air so smaller changes produce larger effects.
Also we can agree on the basic principle that if an object in a flowing fluid (air, water, sausage gravy, etc) is moving, it's because the force exerted on that object by the moving fluid is greater than the frictional force between the object and the ground (let's not get into free hanging weights i am not gonna calculate the catenary of a fishing line I'm just not in the mood for hyperbolic trig today and this would be a much longer post) so to simplify, assuming weight is held constant the ideal shape is one that minimizes the surface area being affected by flow (drag) and increase the surface area in contact with the ground (coefficient of static friction).
A round weight is good because it minimizes the flat surface facing the fluid flow. But it also minimizes the surface in contact with the ground (for simplicity we're treating this as a hard smooth surface even though we know that's not true for a seafloor, so let's assume it isn't si king in. work with me here).
A square weight is good because it maximizes ground contact, but it also functions as a nice sail (ok hydrofoil) in the current with a lot of surface area for the force imparted by the moving water to act upon.

So if I was gonna make a "perfect" weight, I would go for a rounded pyramid shape with a flat bottom and rounded edges on top, or a smoothed out trapezoid. With the vote being for the rounded pyramid when you consider a sandy bottom because if it falls over with the base pointed away from the current that's just great: the water can roll around it much in the way a bullet passes through the air. If it falls over facing away, the force from the current would push it into the sand, which is even better.

I am not an expert at anything. Do not mistake me for one.

I could get into other shapes that see action in modern fluid dynamics, but I choose to focus on shapes that can be cast with a simple mold. We don't machine fishing weights.

Also we missed a golden opportunity to name this thread science and fRiction

[jurelometer]

If you are anchored, there are three areas of concern: getting the weight to the bottom,sticking to the bottom , and winding back up.

If you are in a reasonable amount of amount of depth and current, the larger force keeping the weight off the bottom will be the frictional force of the water against the cross section of line, not the current against a typical weight.  There is less friction along the length of the line than across it, so the line orients horizontally which causes lifting force countering the gravitational force that makes the weight sink.  

Any reasonably shaped weight will drop quickly if no line is attached.  So achieving a shape that will drop quickly enough is relatively easy. Faster drop is still important though, and this would be achieved exposing the least amount of surface area on the bottom of the dropping weight, with a nice bullet nose to sweeten the deal. and a nice thin cross section that dod not have to orient is a given direction.  I.e. a long cylinder.

The hydrodynamic forces against the weight on the bottom should be much less. There is a lot less surface area involved overall as there is no water passing under what is buried in the sand, and the current flow is lessened closer to the bottom.  Folks that have scuba dived will tell you that one of the best ways to swim against the current is to hug the bottom. So once we hit the bottom, frictional forces on the weight will be a minimal part of the problem.

So this leads to three observations:

1.  The thinner the line, the more you will hold bottom for a give amount of weight.  The smaller the cross section, the less friction from current, the less lifting force on the weight. I think we sometimes under-utilize the strength of gelspun braid for deep water fishing. Thin is your friend.

2.  What Gary is really trying to construct is a mini anchor with a bit of a curveball:   at the other end of the anchor line is not a drifting boat, but a semi-fixed (anchored object).   The goal would be to create a weight with a top section that will plow under the sand under tension, but the problem will be that the line will be lifting upward and probably a bit in the direction of the current, away from the boat. If you tighten the line enough to pull  the top of weight toward you, the current will be working to lift and dislodge it, unless the weight can plow in so well that you  have effectively set a second anchor for you boat, and might have to come off the original anchor to check you bait  maybe the commercial long line guys have figured something out here. Or mebbe the worlds smallest Danforth anchor with a trip release

The pyramid style sinkers used for beach casting work because the water is moving in the same direction that the line is being tightened   and the water is shallow giving you a flatter angle to hold the line.  So I don't think this will apply to the situation at hand.

3.  I presume that the goal of the lighter weight is less winding effort.  If so, whatever shape you come up with better not increase the resistance too much when winding up, or you are back where you started from, or worse.

If we are talking about a lot of weight (16 oz or more), I would consider something long and thin (like a cylinder).  It would bury itself in the mud efficiently, and could be would up more easily, meaning that you could actually wind more weight with less effort.  It should be the most hydrodynamic shape for the drop that would not need to orientated in specific direction horizontally to achieve the least resistance.  With the short moment arm it would roll less than Gary's disk for the same amount of lead.  Flat sided versions would drift further on the drop, icreasing the amount of line in the water, so I would stick to round.

[snip]
Also we can agree on the basic principle that if an object in a flowing fluid (air, water, sausage gravy, etc) is moving, it's because the force exerted on that object by the moving fluid is greater than the frictional force between the object and the ground (let's not get into free hanging weights i am not gonna calculate the catenary of a fishing line I'm just not in the mood for hyperbolic trig today and this would be a much longer post) so to simplify, assuming weight is held constant the ideal shape is one that minimizes the surface area being affected by flow (drag) and increase the surface area in contact with the ground (coefficient of static friction).
[snip]

A couple issues to consider:

The soft bottom is not a hard surface, so it is not a straightforward static friction problem, The object can displace or to pull under the surface of the bottom, which provides greater resistance.  I would presume that soft  mud or sand underwater behaves like some sort of quasi-fluid.   So you have some sort of complex stacked fluids problem, not a straightforward friction problem,  But I slept through most of physics  I did happen to be awake when the prof noted that surface area does not affect friction.  Just the total force and coefficient of friction.

Current and friction on the line makes this quite a complex problem. I   guess it could be tackled with a fluid dynamics simulator, but once the results squirted out, I wouldn't be much more confident than when we started.

"catenary" is a new one for me.  Just learned a new word   It looks to me like it is the equation that defines the shape of a curve in a chain/rope between to fixed points.  Interesting reading.  Found out that an inverted catenary is the strongest shape for an architectural arch.   Galileo, Bernoulli. Good stuff.  

Curious if it could be applied at all to the situation at hand, as we are dealing with frictional forces that change based on orientation which would be different than the more uniform gravitational force from the classic cateneray example.

Nice to be able to talk a bit of science here

-J

[Brewcrafter]

Brilliant thread this is why I love the folks on this forum.  My only other consideration that I would throw into the ring (no, I'm not going to say we all need to use expensive surveyors plumb bobs as weights to shoot straight down and implant in the bottom) would be the consideration of if the weight is spinning on the way down.  Sure, we all use swivels, but most of them are pretty low tech unless you have popped for the pelagic ball-bearing varietie$.  Getting to the bottom and holding the bottom is one thing: having a presentable bait once you get there is a whole 'nother story. - john

[JasonGotaProblem]

Well I made the classic mistake of poorly defining the boundaries of the system. You are correct that the main force acting upon the weight is that of the current upon the line and the bait etc. As opposed to on the weight itself. However one could argue that we would in effect be talking about holding those constant as well as the weight of... The weight. We're talking about varying the shape. But I failed to make that clear. But still you're correct that the force to be opposed is the not the horizontal force on the weight but the upward vertical force on it from the horizontal force placed on the rest of the rig. A catenary is ironically actually sort of close here though is not the most accurate description because the force isn't centered on the distance between the bottom of the line and where it leaves the water, its obviously closer to the bottom because that's where the bait is. And then you get into the force gradient of the current in the water column (again accurately mentioned but not by me) Thankfully we need not calculate it to acknowledge its there, and focus our efforts on the force in that direction. And I'm gonna have to think a bit more to have a meaningful idea. I'll have to come back to this.

However I will say that caution is needed because a shape that grips the bottom might not be ideal. I get hung up on rocks enough as it is.

You are partially correct re: surface area vs friction. A box with 3 different shaped sides would have the same frictional force regardless which side it slides on as long as the weight doesnt change. But friction and surface area absolutely are related. The reason a 5 washer drag system has more braking power than a 2 washer drag is surface area.

The concept of a catenary and hyperbolic trigonometry in general come up a lot in structural engineering when discussing load distribution. Especially tanh(θ) I believe I remember khan academy covering it well if you're interested in learning more.

But back to the topic at hand the issue is uplift. We could consider the cross sectional area of the line and bait etc and the speed of the current to calculate the minimum weight needed to keep a bait from drifting, but that's not the question. And i still say the pyramid shape (with attachment at the peak) is the most effective sinker shape for this application. But that's not a hill I'd die on.

This is lovely though. I enjoy being able to talk science with people. But relating it to fishing (at least in conversations outside my own head) is fairly new.

Still not an expert.

[gstours]

Thanks 🙏 to all comments and the great information. 🤳 Fishing can be more than fishing.
   This post isn't about pitting us against each other.  👨‍💻  It's an odd subject that everyone may have to decide for them selves.  I wish you all could fish with me in some situations and have some fun.  🧜‍♀️
  As this gets interesting I want to add,  I've used the sorta wide flat bottom weight to back down the current away from the boat, and others with good results.   This said I,m good with fact that when tipped the flat top of the cylinder shape does add friction and the weight can be moved down stream more easily than the round ball.   Some folks call this back bouncing.  Typical in river fishing 🎣. 
  This is important if you can use it to your advantage.   There's more hidden here.
The flat cylinder shown earlier is simply a cat food can mold.  Da.   Pretty easy for a start.   Butt it may have something going on here that can help me.
  The can mold can be poured to any height to make weight butt it's always a cylinder.  I started with a 16 oz weight that was about 3/4 inch hi by about 2 inch wide and this opened my eyes 👀 as to something is going on here that I have to refine.  Your cylinder shape idea makes sense when retrieving the lead/bait in stiff current.  It's a sectional density equation that has variables.   Hopefully heaven can wait.🤦‍♀️
  Thanks for sharing your thoughts and information.  Let's keep this going.   It's free fun.🎣

[oc1]

I don't get it.  Are we re-inventing the fishing sinker here?  If you do not want the sinker to be pulled loose from the bottom by current then either increase the weight of the sinker, put tines on the sinker or add a weighted line ahead of the sinker so the lines pulls more horizontally and less vertically.  If you do not want the sinker to hang up on obstructions then give it a rounded shape.  Same as anchoring a boat or anything else.
-steve

[Gfish]

Here's the "tine" thing. This one does well in surf/sand and might work on a muddy bottom. The tines will snap out of this position(pointing backward from what's showen) in case of a snag-up

[jurelometer]

Thanks 🙏 to all comments and the great information. 🤳 Fishing can be more than fishing.
   This post isn't about pitting us against each other.  👨‍💻  It's an odd subject that everyone may have to decide for them selves.  I wish you all could fish with me in some situations and have some fun.  🧜‍♀️

Yep, Always tricky.  The ideas need to compete, not the egos. 


Getting back to the topic...

While it is a bit of a simplification, I think it is pretty well settled that frictional forces are  independent of surface area.  When the same amount of force is spread  over a larger surface area, the larger set of imperfections on the surfaces are grinding against each other with less individual force.  It ends up being a wash.  Multiple drag washers in a stack is like dragging multiple blocks across a table. These are different pairs of surfaces that are not directly interacting.

Here is the first link that I came across from a university course, but there are plenty of others:
http://zebu.uoregon.edu/1999/ph161/friction.html

"In general frictional forces are independent of the area of contact although this is an empirical observation not a theory."

Designs intended to maximize surface area in order to increase static friction will probably be less successful.

I don't get it.  Are we re-inventing the fishing sinker here?  If you do not want the sinker to be pulled loose from the bottom by current then either increase the weight of the sinker, put tines on the sinker or add a weighted line ahead of the sinker so the lines pulls more horizontally and less vertically.  If you do not want the sinker to hang up on obstructions then give it a rounded shape.  Same as anchoring a boat or anything else.
-steve

Yes. We are re-inventing the sinker    Or more specifically, deciding what sinker works the best on a deep drop in current.    I don't think a new design is required.   Choosing wisely means less effort to wind up.   

I don't think anchor chains or tines will work for the reasons mentioned in my previous post. 

-J

[smnaguwa]

Following on Gfish suggestion, the Ulua(GT) fishermen in Hawaii use lead with copper/bronze wire protruding from the bottom and bent perpendicular to the lead axis, duplicating an anchor. The wire size is chosen so that it would straighten without breaking the line. Easy to do even making your own sinker.

[JasonGotaProblem]

Yep, Always tricky.  The ideas need to compete, not the egos. 

Agreed. We are both trying to head toward discovering/establishing truth not dominance. Disagreement is healthy when well expressed.

Getting back to the topic...

While it is a bit of a simplification, I think it is pretty well settled that frictional forces are  independent of surface area.  When the same amount of force is spread  over a larger surface area, the larger set of imperfections on the surfaces are grinding against each other with less individual force.  It ends up being a wash.  Multiple drag washers in a stack is like dragging multiple blocks across a table. These are different pairs of surfaces that are not directly interacting.

Here is the first link that I came across from a university course, but there are plenty of others:
http://zebu.uoregon.edu/1999/ph161/friction.html

"In general frictional forces are independent of the area of contact although this is an empirical observation not a theory."

Designs intended to maximize surface area in order to increase static friction will probably be less successful.

I mean I don't entirely agree with the way you're presenting your argument, but in general I will agree that i was wrong to consider drag from the weight against the ground as a factor that could be increased by more surface area.
What one needs to consider is that the balancing effects that minimize the differences in frictional force caused by do hit critical points. Coefficients of friction usually have a range of validity. Making the comparison to something loosely related, think of terminal velocity, where an object in free fall's speed will be eventually limited by mass. even though, as Galileo demonstrated, a solid and hollow sphere of the same diameter fall at the same rate when dropped at heights that can be reached by climbing stairs. But with advances in aeronautics we've been able to see how that observation doesn't hold when they are dropped from the upper atmosphere. This is all to say that the effects of friction (and in fact many forces) aren't always linear, and the simplifications one would use solving intermediate level physics homework problems don't always hold in the real world. That doesn't mean they aren't useful for teaching the concepts or for calculating expected values in intermediate ranges.

And I am absolutely not trying to say any of this condescendingly, I'm shooting for a rigorous response because I've fallen short of expressing myself in previous posts. and i worry that text doesn't convey tone so i feel I should state that directly. I'm enjoying this discussion because it's forcing me to think about topics i haven't considered in a decade, and i appreciate you indulging me. However with that there's always a solid chance I'm getting it wrong.

[RowdyW]

Upper atmosphere? Who fishes from an airplane or rocket ship??   

[Dominick]

Rudy, reread the previous post.  The concept of forces is the key, whether it is water or air, it is the forces that push and pull at the weight.  Dominick