fishordie79 Posted November 4, 2020 Report Share Posted November 4, 2020 Hi All, Just poured some beautiful resin casts and now it's time to weight them. Maybe Vodkaman Dave can answer this or maybe others can as well, but, does anyone know the math that I can use to determine how much weight to add to my casts to make them suspending at various depths? These will be jerk baits from 7cm up to 15cm. I'm sure I could do a lot of trial and error but I am equally sure that someone here can save me the time and lost material. Thanks to you all! Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted November 4, 2020 Report Share Posted November 4, 2020 The spreadsheet that you requested (sent) will get you very close, but as for controlling the actual depth, although technically possible, the differences in water temperature from day to day will mess up that data. Also the actual make-up of the water and its minerals will make slight changes to water density. As a jerk bait, there is nothing to keep the lure down at a depth. The line resistance is always going to pull the lure up to the surface. Having never fished a jerk bait, I could be wrong on this, but all the videos I see of jerk baits, they are all on the surface or just below. Dave Quote Link to comment Share on other sites More sharing options...
fishordie79 Posted November 5, 2020 Author Report Share Posted November 5, 2020 Dave, Thanks for the response man! I do understand that changes in water temperature, mineral content, etc. will affect water density and therefore sink rate and other things. What I am thinking with these baits is an idea I got from some big gliders I bought from Westin. Those gliders sink to between 1.5 and 2 meters and then suspend depending on the factors you stated above. I designed the master for these casts to be somewhat thinner and more tapered toward the tail than the Westin gliders with the intention of them having a more erratic action when fished like a jerk bait. I fish lakes and rivers that vary greatly in depth and weed cover and my intention is to make a variety of these jerks to fit whatever situation I may find myself in. For example, when pike move into the more shallow bay areas before the spawn begins I can often find them in shallower, weedy areas where I would like to get a bait to suspend a couple of meters down but not far enough that it is constantly in the weeds. Another example would be when the perch are feeding close to the surface on summer mornings it would be great to have a small jerk that would suspend about .5 meter below the surface. I will use your spreadsheet to attempt to make something close to what I am envisioning and will let you know how it goes. Once again thank you! 1 Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted November 5, 2020 Report Share Posted November 5, 2020 I am sure that I have worked on this idea before, I seem to remember doing calculations. The problem is testing at home. I thought about clear tubing, but it was ridiculously expensive. I think at the time that I worked on this idea, my gram scale was only 1DP (decimal point) which is simply not accurate enough for the job. I will look into it and see if I can find anything. Dave Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted November 5, 2020 Report Share Posted November 5, 2020 (edited) OK, I have done a few minutes research. The conclusion is that a lure set to sink slowly, will continue to sink at the same rate regardless of depth. Something has to change either with the lure body or the water. The lure body could compress under pressure which would reduce the volume. BUT if the volume decreases then the lure will sink faster. Deep divers experience this. Near the surface the human body is buoyant, there is a net upward force. As the water pressure compresses the body, the volume is reduced eventually to the point were the body has a downward force - so we can discount compression of the lure body. The other thing that changes is temperature. The temperature is always warmest at the top and cools the deeper you go. As temperature of water increases then the density decreases. The numbers are extremely small changes from the 4th decimal place. But still, this change will set a depth for a lure, but it is way beyond our weight and volume measuring capability. The best that you can do is build a slow sinker and time it's decent. Even if you did build a lure that hovered at say 10m depth due to a temperature variation, the time that it would likely take to reach that depth would make the exercise nonsense. Sorry that I cannot bring you a more positive answer. Good question though Dave Edited November 5, 2020 by Vodkaman Quote Link to comment Share on other sites More sharing options...
Travis Posted November 5, 2020 Report Share Posted November 5, 2020 Easy, 100% accurate, on the water....suspend strips or dots. Golf head lead tape the cheaper option. Quote Link to comment Share on other sites More sharing options...
fishordie79 Posted November 5, 2020 Author Report Share Posted November 5, 2020 @Vodkaman No problem man that for me is a positive answer. Puts me in the direction of building the jerks for specific sink rates as opposed to trying to make them suspend:) @Travis Thanks man I'd never heard of suspend strips! Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted November 5, 2020 Report Share Posted November 5, 2020 What I should look into is sink rates. My design tools (posted yesterday) enable the builder to control the percentage of float of a lure, or even measure an existing lure's float qualities, to a high degree of accuracy. What I should do; is equate those float/sink percentages to a m/s or feet/s rate of fall. That would be impressive! Dave Quote Link to comment Share on other sites More sharing options...
fishordie79 Posted November 5, 2020 Author Report Share Posted November 5, 2020 And extremely helpful:) In the meantime I guess I can fix a measuring tape to the side of my testing tank and do some timed drops to work out the sink rate that way. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted November 5, 2020 Report Share Posted November 5, 2020 1 hour ago, fishordie79 said: And extremely helpful:) In the meantime I guess I can fix a measuring tape to the side of my testing tank and do some timed drops to work out the sink rate that way. I am working on it, but I just cannot get the math to work. It would only be a guestimate in any case, as the falling shape of the lure (area) is a part of the equation, and the cross sectional shape. It is all about the coefficient of drag. I will work on it a while longer, but will probably have to let it go, like I did last time. Dave 1 Quote Link to comment Share on other sites More sharing options...
mark poulson Posted November 5, 2020 Report Share Posted November 5, 2020 I can get close by test floating a jerkbait in 60 degree water in my shop. My water gets colder than that, but I use is as a starting point. On the water, I can adjust the float/sink by using either monofilament, which floats, or fluorocarbon, which sinks. Close counts. As long as the bait moves very slowly, either up or down, at rest it will work. Having the patience to test in the shop is the key, because I start with a known quantity that I can adjust on the water. 2 Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted November 5, 2020 Report Share Posted November 5, 2020 OK, I think that I have cracked the sink rate calculation. Because the plan view shape and cross sectional shape cannot be tabulated, I have used the lure volume and the lure length to calculate the dimensions of a cylindrical body and applied the sink rate formula to this compromise body. I have to say that the numbers look very good. All you have to do is enter the lure length, the lure weight and use ‘Archimedes Dunk Test’ to enter the lure volume. The green boxes show the percentage float (less than 100% = sinker) and the sink rate in inches. The tool is another spreadsheet. PM me your email address if you want to have a play. Dave 1 1 Quote Link to comment Share on other sites More sharing options...
fishordie79 Posted November 6, 2020 Author Report Share Posted November 6, 2020 PM sent and awesome man! I’ll share the data with you once I’ve gotten to the testing phase. 1 Quote Link to comment Share on other sites More sharing options...
UKandy Posted November 12, 2020 Report Share Posted November 12, 2020 On 11/5/2020 at 5:00 PM, Vodkaman said: OK, I think that I have cracked the sink rate calculation. Because the plan view shape and cross sectional shape cannot be tabulated, I have used the lure volume and the lure length to calculate the dimensions of a cylindrical body and applied the sink rate formula to this compromise body. I have to say that the numbers look very good. All you have to do is enter the lure length, the lure weight and use ‘Archimedes Dunk Test’ to enter the lure volume. The green boxes show the percentage float (less than 100% = sinker) and the sink rate in inches. The tool is another spreadsheet. PM me your email address if you want to have a play. Dave Now that's a handy little spreadsheet! Good work Andy. Quote Link to comment Share on other sites More sharing options...
