Achieving neutral buoyancy

62 posts in this topic

Clemmy/Vodkaman,

I call foul! No fair talking in engineer talk. My computer doesn't have an automatic translate feature, and neither does my brain.

Are you saying you can take the volume of the lure, calculate weight of the water it would displace, figure out the weight of the lure minus the ballast holes, calculate how much lead (along with an allowance for the finish) is needed to reach the weight of the displaced water, to achieve neutral buoyancy, and go from there?

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Vodkaman, I read and re-read that explanation. I still don't know what I read. But, I have come to a conclusion. Your water in Liverpool is different from my water in Kentucky. I think your test tank has some Vodka mixed in the water. :lolhuh:jk

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I will try really hard to come up with a simple explanation. You should know by now that explaining is not my strong point.

Mark, correct.

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VodkaMan, nothing immmersed in water will displace the same WEIGHT of water. It will displace the same VOLUME of water (Archimedes' principle: Eureka!!), so your calculations are a bit off, when you say that 22.4 g of lure displaces 22.4 g of water. Incorrect. You have to measure the volume of water displaced (using change in depth of water in the jug), to find the volume of the lure and external weight. Also, because the lure has a volume of X cubic cm, it will not weigh X g unless it it composed of water. Come on!! And volume is determined by dimensions: the lure has the same volume after you put the lead into it, it just now weighs more due to different density. It is a composite of two materials, in the same physical space. Volume of lure is unchanged.

A very buoyant lure (ie. floating) displaces less water because of its buoyancy. A sinking lure displaces more because it enters the water, and immerses its full body volume. So the principle does not apply perfectly to all lures. A suspender that floats very slowly is still a buoyant object, so your volumetric calculations have to be take with regard to the amount of body IMMERSED in the water. This is the only part of the lure that can displace water. Buoyancy counteracts weight, so only physical displacement can change water level.

The second part of reasoning with regards to internal vs external, removal of material, and changes in buoyancy due to this and paint and topcoating holds water (pardon the pun).

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Grrr... Just what we need, another guy who actually knows what he's talking about!

Welcome into the pool Shortlite.

Maybe you can explain how obnoxious people, like exwives, keep coming back up no matter how much you weight them under. There must be a formula for that.

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Hahaha, thx for the welcome. Now, not advocatingviolence or anything illegal, but the best thing to do is to beat all the air out of 'em (reduces buoyancy) and add lots of external concrete ballast (preferably encased). No formula, just overkill!

Didn't mean to ruffle feathers going into buoyancy and stuff. Maybe them 1/8 oz balsa lures weighted with 1/2 oz of lead really do float/suspend in vodka? Seriously, doing an accurate calculation is tricky. Getting very close is tricky. So just stick the damn thing in water, add the external ballast, and try and get it to suspend. When it comes to actually drilling out and putting the lead in, take away a little of the lead. Also, test with all the hardware fitted to the lure.

I through wire my carved wooden plugs, and drill out the hole to accept the lead, then seal and test. After that, I reckon the epoxy to seal in the lead, paint and topcoat will add more weight too, so I go for enough lead to make the lure float slowly. That's for a suspender. If I still want it to float, then I reduce the lead I put in some more.

Edited by Shortlite

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Works for me. Both topics.

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Shortlite. Welcome to TU. No feathers ruffled here. I agree with all that you say, it's all about the volume. I just didn't manage to get it down on paper very well.

I have written another explanation, but the pictures and/or the PDF's are too big and I don't have the tools to fix this problem, as I am in work at the moment. I will re-post this evening.

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just stick the damn thing in water
Welcome Shortlite, that's word of wisdom sorely needed in this discussion Sometimes the best course of action is to just do it!! We are lure makers and not engineers so we do not need to over analyze things. After all, the end result from all means is to get the damn lure to suspend:yeah:.

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Whats that saying.... Be careful what you ask for, you just might get it.

My brain hurts,maybe I should just stick to floating baits.

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Vodkaman,

Any chance you would want to "share" the spreadsheet your are talking about? Or maybe give us a taste of a similar spreadsheet that we could plug in the variables and it could tell what the weight of the ballast should be? I would be more than happy with a lure that would rise or fall just slightly, no need for it to "hover", most fish do move some, even at rest something is moving.

FERG

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Ferg, no problem, PM me your e-mail.

This vid is based on my earlier post. It's just a demo, not a teach-in. It may answer a few critics.

There again, it may not.

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Hahaha. I was just pointing out that the calculation was flawed. Background in Engineering and Science; instinct.

Just stick the damn thing in the water!!! Add a little lead. Always going to be trial and error, because (especially with wood) no two pieces will ever be exactly the same. Too many variables. Bottom line in what I was saying is that no lure has the same density as water, because it is a different material. Only water has the density of water. What you get in suspension is an equilibrium of forces. Buoyancy negates weight (which is a force, not a mass: nothing weighs 3 g, it has 3 g of mass).

A composite of wood and lead (lead inside a wood body) has a different density than plain wood or plain lead. The calculations for external ballasting is easier than internal ballasting, for this reason. Complex dimensional shape, placement of the lead, etc. Let's just say that simplifiying the density thing, a 8 cm long cylinder of 1 cm diameter has a volume of 6.284 cubic cm. Internal lead weighting doesn't change its volume, just its mass. So 3g of lure + say 5 g of lead has a total mass of 8 g. Density is mass/volume = 8/6.284 = 1.27 g. Greater than density of water. Full stop. If this lure suspends, it is because it's buoyancy is equal to its weight. 8 g of mass weighs 80 Newtons (force). Mass is scalar, Force is vector quantity. Mass just "is", force "acts" on an object or in a direction.

Just stick the damn thing in the water!!!!! Hahahahahahaha. Spending too much time trying to work that crap out = waste of time = less productivity = less lures made = loss of fishing time = less fish caught!

Git 'er done, git 'er wet, catch some fish!!!

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Nice video. Spot on. Care to share the spreadsheet program? I assume it takes into account lure material, density, etc? Sounds and looks like avery useful tool to get you in the ball park, where you then just adjust a little to get what you want. However, I still stand by my statement that you need to put the fittings, spit rings and hooks on before doing the ballast testing: those extra grams will definitely change the attitude of the lure.

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Shortlite, thanks for the PM and for the comments above. PM your e-mail and I'll send a copy.

The spreadsheet is not finished completely yet and is not of any real use. When finished, it will take into account the lip, all the hardware, paint and epoxy. I believe even paint will make a difference.

The epoxy is the tough one, as it will be down to the builder to be consistent in the application.

The aim is to be able to determine the ballast and fit it with confidence early in the build, with no further testing required. Well, you have to give yourself a challenge.

Appologies to Carpoleo for all the tech talk, but you just might end up with something that helps.

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Awesome mate! Paint and epoxy up to the builder though. Lip and hardware assume total uniformity, or very little variance. Great if you have laser cut bibs, etc. Split rings and hooks shouldn't have enough variability to greatly affect that. I suppose you'd have to build up a components database in addition to that, wouldn't you?

Definitely a great idea. Will PM you, cheers.

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Vman,

Just an idea for calculating the paint/topcoat in the spreadsheet. I know you are doing it for you, but you also may change (develop?) your paint/clearcoating process... Why not have a function built in to allow for paint/clearcoat. My thinking is that if you weighed a few baits before and after painting/clearcoating, it should give you a ratio of before and after. This ratio could then be used as a function to apply to the spreadsheet calculation adjusting to your way of painting/clearcoating, i.e. brand, application thickness, # of coats, etc.

Of course you may also need a seperate one for foiled baits, or for "toothy" fish neccessitating more epoxy coats, but hopefully you see the idea....

Also given that densities are normally published at, I believe 20 degrees celcius, you should be able to input a desired fishing temperature constant.....

One further complication (lol) is that monofilament line will act as a buoyant force, fluorocarbon a ballast....

Hope this helps???

Craig

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Vodkaman, Thanks for super video. Definitely not an engineering mind here, I mostly rely on trial and error. The video is quite inspiring and just watching has helped me a lot.

Thanks again

David

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Great Job! Looks like it worked slick to me.

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Do we need a different spreadsheet and lure for each 3 or 4 degrees difference in water temperature we might be fishing? And will we need a different set of lures for each water column we will be fishing in?

About 6 of each deep, medium, and shallow divers (to cover the temperature variations) in about 5 different colors should cover the days fishing for suspending lures. 6X3X5=90 lures. Might be a few more for extreme conditions.

Or if we know the water temp prior to departure we could just swap out the box with the lures for that temperature of water.

Then I will still need to pack the cranks that rise and the ones that back up on the rise and the Rattle Traps Jerkbaits and the jointed swimbaits.(I have got to be leaving something out)

I just realized that I will need 3 different sizes of the suspending baits so that takes my total to 270 suspending baits + all the others. Will 5 colors be enough?

This is all just in fun.

The cool thing is that most lure builders that read this thread will get something out of it that will help them in some way or another.

Edited by Palmetto Balsa

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Clemmy, you are on the same wavelength. Yes, the epoxy and paint will be a before and after estimation. So the builder will have to finish one first, to extract this infomation. Extra entries will be built in for foil and fins. If not used, just enter zero.

Shortlite, I am thinking of a components database too. But, the builder will weigh a number of hooks, type in the weight and the number that he weighed. The spreadsheet will work out the volume of the hook etc. The same for split rings, quick releases etc. This would take care of variations between hook types. This would only have to be done once for each item. I will add extra lines that can be defined by the builder.

Lips will be dealt with by material type. The builder will enter the weight of the lip against the material used, also the thickness and a rough estimate of percentage glued in the body (10 -20%), this should get us close.

I am planning on including water density, for the salties. It will also allow those that are concerned enough about water density to still play. I'm sure I could do something with temperature too.

The spreadsheet is not just about suspenders, it is designed for all types of lure and will help to achieve repeatability between lures. The builder enters a percentage that represents its buoyancy. The builder enters 100% for a neutral buoyancy, or 95% for a slow rise, 105 for a slow sinker, and so on...

I am accepting any suggestions, but the danger is making the thing too complicated, seeing as it was developed to make the job simpler.

Edited by Vodkaman

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It's already getting there by the sounds of it. Calculating the volume of a hook? Bloody hell..... Well, if you want one set of lures for specific conditions and another set for others, then you will end up with 90 crankbaits in a box.

Water temperature and salinity plays a bit part as well. Varying salinity occurs depending on where you fish, and even conditions. Playing with you lures and adapting is one of the keys to success, but keeping down the amount of gear you are slinging is also important. Sticky putty, SuspenDots and SuspenStrips work for those times when you have to weight the bait down to get it to act right. So I just go for a slow float in fresh water, then tweak it when I fish brackish or fresh. You can swap for a thicker wired treble, go up a size, heavier split ring, drop down a size, etc. No need to get all bent out of shape and overcomplicated with calculations and computer programs. Repeatability is fine if you want to be stuck there forever, but need to guarantee the same performance for each bait you produce, ie. ones for sale.

Don't waste fishing time!!! We all know tuning is a part of the game. Get close, and do the rest on the water with whatever is at your disposal.

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Personally, I don't fish, so hopefully I can save everyone else some fishing time. Everything you have said is true and because of all the inputs and variables, we can only expect to get reasonably close. Every measurement has errors and these will accumulate, so don't be expecting majic, just close. Adjustment on the bank would still be necessary.

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Shortlite, you gotta excuse the guy for trying to help, he thought someone asked for it.

If you want to get into the ballpark, pay attention to the video he so generously provided & there you go, no density factors, salinity factors, temperature factors, pressure factors, or added components.

Take some lead wire with you & adjust on the water, ignorance is bliss.

But don't rib the guy for wanting to comprehend the fundamentals & making an effort to provide a tool to better inform those interested.

To each his own, if the class is too hard, drop out & go fishing

Edited by redg8r