Correctly calculating ballast for desired bouyancy?

[exx1976]

Scientifically, I understand the entire process.  Archimedes, the works.

 

(every time I hear the name Archimedes, I think of this scene:)

 

https://youtu.be/B8h5Owjxomg

 

Anyhow...  What I'm wondering is less the *science* of it, since that's easy enough (for me) to understand, and more about the practicality of the application.  For example, I don't believe my baits to be watertight until after the topcoat of epoxy has been added - at which point it's FAR too late to be adjusting ballast.

So, at what step are you guys making this determination?  Or are you determining it once per type of wood you're using, and then just adding that much ballast to every bait of that type made from that same type of wood?

Interested to hear how this process is being done by others.

[Vodkaman]

Well, the basic answer is that you 'wing it', but obviously there will be more scientific ways to determine neutral buoyancy with a top coat. Personally, I do not apply topcoats to my lures as I only build prototypes. I am not a regular fisherman so I do not concern myself with hook rash and other topcoat issues like aesthetics.

If I were to apply a top coat then this is how I would do it:

First job is to consider 'knowns' and 'unknowns'. What information can we easily access about the top-coat. The density of the top-coat material is fairly easy to determine. We can pour a sample, weigh it and use Archimedes to measure the volume, divide the two numbers to calculate the density (g/cm³), or read the top-coat specifications.

We can weigh the lure body before and after top-coat application, assuming that you consistently apply the topcoat the same every time. So, now we know the weight added to the lure, the volume added to the lure. We could even determine the surface area of the lure but this would not be necessary.

If I were using top-coats, I would add this information to the spreadsheets. The reason that I did not is because I wanted to keep things as simple as possible.

I have sent you the spreadsheets as requested. Have a play with them, adjust the numbers and get a feel for how they work. THEN, if you want a top-coat section to be added in then let me know and I will produce a special. It is something I will eventually do for my own use as I do have a lure under development that I may take to the next stage.

Love the movie clip from 'Pi (1998)'. I did not rate the movie high enough to keep.

Dave

Edited November 26, 2020 by Vodkaman

[exx1976]

3 minutes ago, Vodkaman said:

Well, the basic answer is that you 'wing it', but obviously there will be more scientific ways to determine neutral buoyancy with a top coat. Personally, I do not apply topcoats to my lures as I only build prototypes. I am not a regular fisherman so I do not concern myself with hook rash and other topcoat issues like aesthetics.

If I were to apply a top coat then this is how I would do it:

First job is to consider 'knowns' and 'unknowns'. What information can we easily access about the top-coat. The density of the top-coat material is fairly easy to determine. We can pour a sample, weigh it and use Archimedes to measure the volume, divide the two numbers to calculate the density (g/cm³), or read the top-coat specifications.

We can weigh the lure body before and after top-coat application, assuming that you consistently apply the topcoat the same every time. So, now we know the weight added to the lure, the volume added to the lure. We could even determine the surface area of the lure but this would not be necessary.

If I were using top-coats, I would add this information to the spreadsheets. The reason that I did not is because I wanted to keep things as simple as possible.

I have sent you the spreadsheets as requested. Have a play with them, adjust the numbers and get a feel for how they work. THEN, if you want a top-coat section to be added in then let me know and I will produce a special. It is something I will eventually do for my own use as I do have a lure under development that I may take to the next stage.

Dave

 

Thank you for the reply!  Unfortunately, perhaps I was a bit unclear in my initial question.  What I am wondering is more *when* in the process one performs the Archimedes test, and if it is sufficient to perform it on only a single example of a bait that is made the same shape and from the same wood each time?  If this is the case, then it's relatively easy to create a "sacrificial example" for the purposes of gathering this data.

However, if guys are doing this every time, how are you accomplishing it without compromising the bait?  It just seems to me that, logistically speaking, it is difficult to work into the process because you don't want to get the bait wet until it's sealed, but once it's sealed, adjustment of the ballast becomes MUCH more of a challenge.

Hopefully that clarifies my request.

[Vodkaman]

All will fall into place when you see the spreadsheet, but let me outline the process for everyone.

If the lure was a cast body then the density and volume would only have to be determined once. BUT, with wood, the density can change from different areas on the same block. Also no one can carve accurately enough to make the volume repeatable to even one decimal place, so body volume is measured for every build.

Fortunately, this step is done BEFORE drilling holes. Simply carve the body, add a temporary seal coat, I use thin Superglue (CA glue), then do the Archimedes test. Input the information in the spreadsheet.

You then enter the hardware information in the hardware section, play about with the ballast weight number until you get the float percentage that you require.

Then you can drill the holes for the hardware and ballast and finish the lure. Nothing is sacrificed.

Dave

Edited November 26, 2020 by Vodkaman

[exx1976]

19 minutes ago, Vodkaman said:

All will fall into place when you see the spreadsheet, but let me outline the process for everyone.

If the lure was a cast body then the density and volume would only have to be determined once. BUT, with wood, the density can change from different areas on the same block. Also no one can carve accurately enough to make the volume repeatable to even one decimal place, so body volume is measured for every build.

Fortunately, this step is done BEFORE drilling holes. Simply carve the body, add a temporary seal coat, I use thin Superglue (CA glue), then do the Archimedes test. Input the information in the spreadsheet.

You then enter the hardware information in the hardware section, play about with the ballast weight number until you get the float percentage that you require.

Then you can drill the holes for the hardware and ballast and finish the lure. Nothing is sacrificed.

Dave

Ahh.  The temporary CA seal coat is what I was missing.  That's the step that prevents water intrusion.

I use minwax sanding sealer on my baits.  Would you recommend I do that, and THEN the CA, or can I simply do the CA and omit the sanding sealer altogether?

[Vodkaman]

I would say Minwax the body if that is your chosen sealing plan. Then start up the spreadsheet once the seal is dry. The CA is only to keep the water out for the few seconds it takes to determine the volume.

BUT, actually, the spreadsheet does not require you to use Archimedes on the body (I forgot how to use my own spreadsheet). People who make large bodies will find it impossible to measure the volume because the container of water will be too heavy for the gram scale.

All you have to do is enter the weight of the carved body. The density of the wood is determined from just a sample (1st section of the spreadsheet) so it is all a little simpler than I described.

I guess that it is possible that the minwax could affect the numbers. Let me know if you have any problems.

Dave

[exx1976]

1 hour ago, Vodkaman said:

I would say Minwax the body if that is your chosen sealing plan. Then start up the spreadsheet once the seal is dry. The CA is only to keep the water out for the few seconds it takes to determine the volume.

BUT, actually, the spreadsheet does not require you to use Archimedes on the body (I forgot how to use my own spreadsheet). People who make large bodies will find it impossible to measure the volume because the container of water will be too heavy for the gram scale.

All you have to do is enter the weight of the carved body. The density of the wood is determined from just a sample (1st section of the spreadsheet) so it is all a little simpler than I described.

I guess that it is possible that the minwax could affect the numbers. Let me know if you have any problems.

Dave

Well, wait...   Didn't you say that wood density can vary? I haven't looked at the spreadsheet very closely..   I'm guessing the lure volume is entered in a separate cell, thus by weighing subsequent bodies (assuming they are all pretty close to identical) the weight (along with the example determined volume) will provide the density, yes? 

[Vodkaman]

Yes, the body volume is automatically extracted from the density and the weight.

You can choose to use the carved body for the Archimedes test or choose a separate piece, it is up to you. Because the spreadsheet could be used by someone making a 12" body, I had to make the tool usable by all.

Dave