Underwater Sound vs. Hydraulic Pressure Wave

[MRoberts]

Ok I have been trying to think of a way to address this topic and not sound like I was an applied physics major for two year, before switching to engineering.

We all know that if you throw a pebble into a glass calm pond it forms a serious of ripples that spread out in all directions. These ripples move until they strike something or the resistance of the water slows them down to a point where they a undetectable. This type of phenomenon is what I am referring to when I talk about Hydraulic Pressure Wave. (HPW)

A HPW is created every time a bait strikes the water and then as a bait moves through the water. When an object is underwater it is sending the HPW in all directions. My question for someone who completed there degree in physics is, at what speed and how far will these pressure waves travel.

From what I understand, the HPW’s are what the Muskies pick up with there lateral line. Supposedly the lateral line only has a limited range, but what is the range. By watching ripples move across the water my guess is that the HPW’s don’t move very fast, and would leave a cone of influence behind a bait. If this cone of influence contacts a musky you may get a response. But can the fish tell how far it is from the source or does it just move until it contacts the source?

Or am I totally wrong, does a Hydraulic Pressure Wave act more like sound in water, does it move at the same speed as sound in water, though that is obviously undetectable to us.

I know this has been talked about before, but what exactly is picked up by the lateral line? Is it the pressure wave or some other vibration related to the pressure wave?

Well that should be a good place to start.

Thanks

Nail A Pig!

Mike

Let 'em go, Let 'em Grow

[Bob Babcock]

Mike,
I e-mailed your question to a high school physics teacher friend of mine. He's not much of a fisherman, but when he responds I'll let you know.

[jlong]

Mike,
I wasn't a physics major either... but have my share of credits in that field as well. I can't tell you how quickly a pressure wave dissipates in water... but I do have some idea how the lateral line works.

Basically it is like a giant ear. There is a canal containing neuromasts (tiny little hairs). When a pressure wave... or displaced water hits the lateral line there is acceleration of water through the canal. The increased velocity moves the neuromasts which then transmit and translate that stimuli. It provides EXTREMELY accurate input to the location of the pressure wave source. Even more accurate than the ear can determine the location of audible sound sources.

The lateral line is sensitive to LOW frequency waves that the ear cannot detect. The ear, however, is sensitive to higher frequencies the lateral line cannot detect. Thus, fish have a need for both and are sensitive to a much WIDER range of vibrations than other animals.

My personal beliefs are that fish use the inner ear for balance and protection... and the lateral line has been refined for feeding. That's why I favor water displacement rather than sound as a strike trigger.

I like your thinking, however, in regard to figuring out how far away from you LURE does it's pressure wave travel. Can one lure displace more water and therefore produce viable lateral line stimuli to greater distances? That certainly would make a lure more effective since you wouldn't need to get it as close to the fish in order to elicit a response.

Hopefully there are more physics and biology buffs out there that can humble us some more with this topic.

jlong

[MRoberts]

I think that the pressure wave is why the slower retrieve seems to work better in dark water. My favorite bucktail in my dark water flowage is a Boo Tail. Could it be that the big Colorado blade and the slower speed have something to do with it. The bait isn’t out running it’s cone of influence as fast. Burning a bucktial in this water has never done well for me, unless it was a vibrex, with it little ringing bell. There’s that sound thing working again.

So after working through this, coming up with a few terms I never thought I would use relating to muskie fishing (Cone of influence) here are my conclusions.

If you are fishing dark water it really pays to use a slow bait, or give a fast bait long pauses to give a fish hunting the pressure wave a chance to catch up to it.

If you really feel the need to fish fast, rattles or a loud surface commotion would probably help the situation. That way, you aren’t totally relying on bring the bait across an ambush point. A fish may still hunt the sound.

Jason may be right the sound might not trigger a strike, but it still could bring the fish close enough so the visual or lateral line could. Options! Options! Options!

Nail A Pig!

Mike

Let 'em go, Let 'em Grow

[jlong]

Mike, I really like the new term you coined. "Cone of Influence" really describes it well. My simple point is that I feel that audible sound is not a part of that "cone of influence". Perhaps sound may help attract a fish towards your lure and increase your chances of it encountering your lure's "cone of influence"... but it doesn't help trigger a strike.

Maybe that is the secret behind the rattle traps. The sound travels much FURTHER through the water so it attracts fish from a greater distance. Then once they get close enough... the strong pulsating vibration of the lure and flash trigger a strike. No wonder those little suckers work so well on shallow flats where covering water is the key.

If I had to choose between a more effective "cone of influence" or "sound"..... it would definitely be the "cone of influence"..... which I feel consists of a visual (sight) and touch (lateral line) element. We all want strikes... not follows.

Oh yeah, and I agree slow is good in dark water. I think it translates to opportunity. Get 'em to react... then give them a target. The only problem with slow is you have to know where the fish are.... otherwise it is a long search.

So its location location location.... not options option options.

jlong

[MRoberts]

Not only does sound move much farther through the water, but it also moves much faster.

I was just looking through my Fluid Mechanics book and now my brain hurts.

What we are really talking about with this Hydraulic Pressure Wave stuff is turbulence. As a bait moves through the water it creates drag forces that create turbulence behind the bait.

There are two types of drag forces for immersed bodies, skin-friction drag and pressure drag. I’ll probably loose everybody here except the analy insane. (Jlong)

Skin-friction drag results from shearing stresses in the fluid layer adjacent to the body’s surface (the boundary layer). Pressure drag results from disturbance of the flow stream as it passes around the body and produces pressure differential between lowered pressure at the rear of the body in the turbulent wake and higher pressure at the front of the body at the stagnation point.

This could explain why the Manta has not produced for me like I thought it would. There is pretty much no pressure drag, as it slides through the water effortlessly. The smooth rounded body also greatly reduces skin-friction drag. Therefore it is predominantly a site lure. I will be painting my bright dark water Manta to a more clear water friendly color and give it a better shot in that situation.

The key for triggering that lateral line appears to be finding a balance between creating as much drag as possible, but still have the lure be retrievable without a 3000# winch.

I still can’t find figures on how far and at what speed turbulence moves, from the path of an object moving through water or how long it takes to dissipate.

Well I am going to go search through my tackle box and find the biggest, bluntest, nosed bait I have and try and tickle the lateral line of a big girl at lunch time. I’ll check back in if it works.


Nail A Pig!

Mike

Let 'em go, Let 'em Grow

[jlong]

Mike, I refuse to blow the dust off my Fluid Mechanics textbook (which is right next to me on the bookshelf here at work) but you just reiterated my claims somewhere on the web about the Manta and its laminar flow. That is why it swings like no other bait (and is hard to stop I might add, it just goes and goes and goes)... but it also produces a laminar flow field behind its travel path... which I call lateral line camoflage.

I've theorized about textured surfaces to create turbulence. You know, make the surface of your bait dimpled like a golf ball (Divani hinted at this on MuskieFirst). My hesitation has been that it would hinder hooking percentage, so I haven't actually tried it.

Prey fish have naturally developed their own lateral line camoflage. Things like the shape of their tail fins for example. BUT, when they struggle... that is now a turbulent flow and they are a vulnerable target. Its like suddently becoming visible on a radar screen.

You can effectively INCREASE your pressure wave without increasing resistance. It is a simple thing called ACCELERATION. The classic stop&go action of a suick is a prime example. Every forward surge of the bait sends a STRONG pressure pulse outwards for nearby predators to detect.

Mike, maybe your Squirkko has been so hot for you because you not only have the acceleration through each turn of the bait... the soft rubber tail continues to produce turbulence while the bait coasts to a stop. That extra "signal" may be what triggers strikes when nothing else will. And let me remind you, that squirkko does NOT have rattles and is a very quiet bait... yet it has been your #1 dark water lure this season. So is sound really essential?

It gonna be a long winter now that my boat is put away....

jlong

[ToddM]

Wow, some interesting thoughts here. Would you say then that a flat sided crakbait would push more water than a rounded one? Some crankbaits have a good vibration, like an ukko wobbler. A jake has less vibration but is flat sided and would push alot of water. How about glide baits? Your right about the manta, it glides very effortlessly. How about a flat sided glider like a cobb's crazy shad or a magic maker? Or a glider with some resistance like a phantom?