Constructive Science... Otherwise Known As Winter Boredom 2025
OkobojiEagle reply :
Known... as water warms it becomes less dense, causing baits that suspended at the cooler temp to sink at the warmer temp. Also known... water pressure increases with depth. Can it be calculated at what increased depth a bait will suspend as the water density is increased with depth?
Another variable...at deeper water depths in lakes, the water temp is most often colder. Can the suspending depth of a bait be reliably calculated based upon the water temp at given depth intervals?
oe
SPEEDBEAD. reply :
I think the difficulty in keeping that bait in the "prime" zone for suspension would be huge, especially if we are talking cast and retrieve lures. The curved ends of a cast with the bait getting to maximum depth and then you reeling back to the boat keep it "deep" for a relatively short time.
Long line trolling a lure may yield more effective results.
Just thinking out loud with you.
lmoore reply :
Water pressure at depth would be irrelevant since it would be acting uniformly over the entire surface of the lure.
For calculating depth of suspension, you would need to know the density of the lure and compare to the density of the water at a given depth, which is almost entirely affected by temperature (assuming pure H20). Plotting the comparison of density and temperature gives you the approximate formula D=-00.14T^2+.0897T+998.65 D+Density(kg/m^3) and T=Temperature (F)
Jmrichardson2011 reply :
Essentially, you are correct this is a function of density. To achieve neutral buoyance (i.e.the condition which causing a suspending bait to suspend), the density of the surrounding water (in a volume equal to that of the bait) must be equal to the density of the bait.
Recall (from physics) that:
Density = m/V (mass divided by volume)
Figuring the mass of of the bait should be easy (just weigh it in grams and convert to kilograms, SI units work much better for these calculations so get water temps in Celsius).
Not sure how to accurately measure volume of the bait except to submerge in a graduated cylinder in a fluid of known density, The volume of fluid it displaces (read on the cylinder) is equivalent to the volume of the bait.
Not just divide your mass in kg by the volume in Liters and you have the density of the bait.
Online, you should be able to find a table of water density versus temperature (most thermodynamics textbooks have them too).
Measure the temperature at the depth you would like to fish, find the density of water using the table, then select the exact density bait.
A long answer to a short question, but you got my engineer's brain thinking and thought experiments like this are always fun to do.
....I am a little bit weird, comes with territory of engineer.... 
BasskingKeith reply :
What's winter?
SPEEDBEAD. reply :
On 2/20/2013 at 1:49 AM, Bank said:What's winter?
It's when your bass spawn. LOL
BasskingKeith reply :
lol I'm kidding. That's an interesting topic, though. The only thing I can think of is how deep do you plan on getting a suspending lure on one cast in order for it to start sinking or floating?. Will it start floating more due to the pressure? Or sink better?
Teal reply :
Dang, i think thats the episode of Mr.Wizard that I missed.
Jmrichardson2011 reply :
Pressure on the bait doesn't play into as much as density. Since pressure is a function of density the exact water pressure on the bait will not affect buoancy. The pressure at a given depth acts equally on the bait in all directions (in a static sense, after the bait has sunk and before retrieve).
roadwarrior reply :
You guys are giving me a headache!
Jmrichardson2011 reply :
Roadwarrior,
After engineering school this is how I think about everything...it's what they drill into our heads.
Sometimes I think the inside of my head would be a very scary place to reside... 
lmoore reply :
It's unfortunate you went to such a terrible school of engineering. 
roadwarrior reply :
My son-in-law is a Civil Engineer, currently working on an interstate project.
Much of his work involves water issues, but some of it is railroad bed composition.
I am not always sure what language he speaks.
Did your school compete in the Concrete Boat Program? That was a lot of work,
but it must have been fun, too. A few years ago the National Finals were in
Knoxville, TN. The team from Seatlle spent a lot of time and money just to get to
the event. An important aspect of the competition is that the canoe must float.
Well, water density in Washington's colder environment is much different than
here in Tennessee. The boat did not sink, but it didn't float either! I guess it turned
into a Smithwick Rogue, suspending a few inches under water.
Jmrichardson2011 reply :
On 2/20/2013 at 2:49 AM, lmoore said:It's unfortunate you went to such a terrible school of engineering
...Must be a Hawkeye...
Go ISU Cyclones
Jmrichardson2011 reply :
On 2/20/2013 at 2:50 AM, roadwarrior said:My son-in-law is a Civil Engineer, currently working on an interstate project.
Much of his work involves water issues, but some of it is railroad bed composition.
I am not always sure what language he speaks.
Did your school compete in the Concrete Boat Program? That was a lot of work,
but it must have been fun, too. A few years ago the National Finals were in
Knoxville, TN. The team from Seatlle spent a lot of time and money just to get to
the event. An important aspect of the competition is that the canoe must float.
Well, water density in Washington's colder environment is much different than
here in Tennessee. The boat did not sink, but it didn't float either! I guess it turned
into a Smithwick Rogue, suspending a few inches under water.
We didn't have a concrete boat program that I was aware of. I spent my nights in the Aerospace building, but the concrete canoe competitions are cool. I spent my free time building rockets.
lmoore reply :
I was a Civil Engineer also and we had the Concrete Boat team, but I was more worried about the ISU Fishing Club. That last one should help Mr. Richardson out.
lmoore reply :
On 2/20/2013 at 2:54 AM, Jmrichardson2011 said:We didn't have a concrete boat program that I was aware of. I spent my nights in the Aerospace building, but the concrete canoe competitions are cool. I spent my free time building rockets.
We had one, but it was entirely Civil and Construction Engineers as far as I know.
Jmrichardson2011 reply :
Now I got it.
At least you are a cyclone and an alright guy to fish with. Now if only it wasn't civil engineering...
On 2/20/2013 at 2:55 AM, lmoore said:I was a Civil Engineer also and we had the Concrete Boat team, but I was more worried about the ISU Fishing Club. That last one should help Mr. Richardson out.
lmoore reply :
On 2/20/2013 at 3:00 AM, Jmrichardson2011 said:Now I got it.
At least you are a cyclone and an alright guy to fish with. Now if only it wasn't civil engineering...
We all have our issues. lol
Jmrichardson2011 reply :
On 2/20/2013 at 3:02 AM, lmoore said:
We all have our issues. lol
That's true
OkobojiEagle reply :
LOL... now that all of you brainiacs have burned off your lunch carbohydrates... what I'm interested in knowing is... when I'm fishing a perfectly suspending Pointer 75 at 5' of depth over 30' of water and the sun warms the surface temp 2 degrees allowing that bait to sink... how much deeper will it sink before suspending again?
oe (my son-in-law is an ISU grad... but he doesn't drive trains)
Jmrichardson2011 reply :
On 2/20/2013 at 6:26 AM, OkobojiEagle said:LOL... now that all of you brainiacs have burned off your lunch carbohydrates... what I'm interested in knowing is... when I'm fishing a perfectly suspending Pointer 75 at 5' of depth over 30' of water and the sun warms the surface temp 2 degrees allowing that bait to sink... how much deeper will it sink before suspending again?
oe (my son-in-law is an ISU grad... but he doesn't drive trains)
That depends on a number of factors - How fast is the water heating up? how much has the 2 degree surface temp increased increased the temperature at 5' in the immediate vicinity surrounding your bait. It beomes a bit of a mess when dealing with transient heating (as the sun does not necessarily heat at an even rate all day). It involves partial differential equations and some magic to get the answer...if you are willing to compensate I am sure I could figure it out for you 
...just kidding.
It may be more fun just to set up an experiment to see how much the bait sinks as the water warms, I think some good electronics or a sonar flasher would be able to do the trick.
RODNEY reply :
Hmmmmm, and I thought I was doing an intellectual thing deciding what colors to tie in my hair jigs.
Rodney
lmoore reply :
On 2/20/2013 at 6:26 AM, OkobojiEagle said:oe (my son-in-law is an ISU grad... but he doesn't drive trains)
Really confused me with this one for a minute since I actually do work for a Railroad. Lol
OkobojiEagle reply :
lmoore... 
Bair reply :
On 2/20/2013 at 1:48 AM, Jmrichardson2011 said:Essentially, you are correct this is a function of density. To achieve neutral buoyance (i.e.the condition which causing a suspending bait to suspend), the density of the surrounding water (in a volume equal to that of the bait) must be equal to the density of the bait.
Recall (from physics) that:
Density = m/V (mass divided by volume)
Figuring the mass of of the bait should be easy (just weigh it in grams and convert to kilograms, SI units work much better for these calculations so get water temps in Celsius).
Not sure how to accurately measure volume of the bait except to submerge in a graduated cylinder in a fluid of known density, The volume of fluid it displaces (read on the cylinder) is equivalent to the volume of the bait.
Not just divide your mass in kg by the volume in Liters and you have the density of the bait.
Online, you should be able to find a table of water density versus temperature (most thermodynamics textbooks have them too).
Measure the temperature at the depth you would like to fish, find the density of water using the table, then select the exact density bait.
A long answer to a short question, but you got my engineer's brain thinking and thought experiments like this are always fun to do.
....I am a little bit weird, comes with territory of engineer....
Lol... then this is exactly what I'll be doing for the next week in physics. FYI they must have done something to you in that engineering school because you are starting to sound just like the physics teacher.
On 2/20/2013 at 6:38 AM, Jmrichardson2011 said:That depends on a number of factors - How fast is the water heating up? how much has the 2 degree surface temp increased increased the temperature at 5' in the immediate vicinity surrounding your bait. It beomes a bit of a mess when dealing with transient heating (as the sun does not necessarily heat at an even rate all day). It involves partial differential equations and some magic to get the answer...if you are willing to compensate I am sure I could figure it out for you
...just kidding.
It may be more fun just to set up an experiment to see how much the bait sinks as the water warms, I think some good electronics or a sonar flasher would be able to do the trick.
And I am still trying to grasp this. Is it only differentiable on a certain interval or time? You lost me.
Jmrichardson2011 reply :
On 2/20/2013 at 11:59 PM, G Bair said:Lol... then this is exactly what I'll be doing for the next week in physics. FYI they must have done something to you in that engineering school because you are starting to sound just like the physics teacher.
And I am still trying to grasp this. Is it only differentiable on a certain interval or time? You lost me.
It is differentiable in both time and direction (mostly just depth, the other directions may be able to be ignored).
To really get an accurate answer is just a long process and a lot of things need to be known (unless you have a lot of extra instrumentation on your boat don't know if these variables could easily be known).
Basically the last paragraph you quoted is the reason bait companies say that the bait will suspend at 3-5 feet as opposed to saying at exactly 4.5 feet (remember, the type of line you use plays into this as well as it also has density and a specific volume). It's just complicated
lmoore reply :
On 2/21/2013 at 12:53 AM, Jmrichardson2011 said:It's just complicated
This pretty much sums it up. If you REAAALY wanted to get an idea, you could make some assumptions to use for estimating, but in order to get an accurate answer, you'd have to give yourself one heck of a headache.
OkobojiEagle reply :
Come Spring I'll follow a very slowly sinking jerk bait under my sonar and see if it stops before the bottom... heck, that's really what I was wanting to know, but there's too much ice on the lake now to push my boat out and check.
oe
(there seems to be more of us Iowegians on this site than I imagined... maybe it's time we dust off the Minniyota jokes!)
lmoore reply :
That, you could figure out if you knew the density of the lure and the bottom temperature. Water density is highest at 39 degrees celsius (1000 kg/m3), so any bait that was less dense than 39 degree water would act as you say under some circumstances.
There sure do seem to be a lot of Iowans around this time of year. Everybody must be almost overcome with cabin fever by this point.
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