Density Vs Sink Rate

[BrierBob]

2 minutes ago, walkercope said:

Oh man I'm not even thinking about paint or clear coats yet.  If you have any suggestions I'd love to hear.

Epoxy is heavy.

[walkercope]

45 minutes ago, danthefisherman said:

Nice! It shouldn’t matter the center of gravity vs the center of volume. If they are offset laterally shouldn’t it just cause the bait to rotate until they are aligned? A well-balanced bait should have a center of mass bellow the center of volume. My senior project was to design, fabricate, and test kayak outriggers so I’ve put a fair amount of thought into this haha.

Yeah my plan is to have the COM below the COV, I think we're in agreement there.  I guess there's two questions I have though:

a) the first question I asked - overall body density vs sink rate?

b) the distance needed between the COM and COV to keep the bait oriented vertically at all times, when burning it and twitches etc?  Like for example looking at a hypershad, it's really impressive how stable it is even when they burn it real fast, and that's what I'd like to achieve ideally.  I'm considering trying to mold in foam cylinders to the top of the bait to move the COM down further.  But I think for now I'm going to try it without the foam and see if it's good enough without to keep it simple.

Theoretically though it seems like if your COM is below your center of the drag force then the bait would tend to nose up.  I'm thinking by spreading the weight out along the length of the bottom of the body I could limit that by giving the bait a high moment of inertia in that axis?

Edited November 23, 2022 by walkercope

[walkercope]

9 minutes ago, BrierBob said:

Epoxy is heavy.

I've read that it's possible to model that too by creating a shell around your model with the expected clear coat thickness and density but I felt like trying to factor that in for now was a bit more than I'm ready to try to handle.  So I think I'm just going to pour some blanks and see how it goes.  Maybe I'll decide that I need a tuning chamber in the future...

[danthefisherman]

53 minutes ago, walkercope said:

Yeah my plan is to have the COM below the COV, I think we're in agreement there.  I guess there's two questions I have though:

a) the first question I asked - overall body density vs sink rate?

b) the distance needed between the COM and COV to keep the bait oriented vertically at all times, when burning it and twitches etc?  Like for example looking at a hypershad, it's really impressive how stable it is even when they burn it real fast, and that's what I'd like to achieve ideally.  I'm considering trying to mold in foam cylinders to the top of the bait to move the COM down further.  But I think for now I'm going to try it without the foam and see if it's good enough without to keep it simple.

Theoretically though it seems like if your COM is below your center of the drag force then the bait would tend to nose up.  I'm thinking by spreading the weight out along the length of the bottom of the body I could limit that by giving the bait a high moment of inertia in that axis?

Now that we are considering bait stability and action, it’s a whole different ballgame. Line tie, joint orientation, cushion of your line, fishing technique… theoretically one could work it all out on paper, but you can’t account for all the variables and all the assumptions made could easily lead to a very different end result. This is why I tend to focus on bait functionality over sink rate, and I find on the water testing much more reliable than playing the guessing game in this area.

If I had the answer I would use it with my own builds, but I’m afraid it isn’t as straightforward as one might think. Keep us updated if you figure it out though. I’m sure you can find some material sink rate experiment online to give you a ballpark feel. Otherwise you can join the rest of us “cavemen” and learn by doing 

[walkercope]

16 hours ago, danthefisherman said:

Now that we are considering bait stability and action, it’s a whole different ballgame. Line tie, joint orientation, cushion of your line, fishing technique… theoretically one could work it all out on paper, but you can’t account for all the variables and all the assumptions made could easily lead to a very different end result. This is why I tend to focus on bait functionality over sink rate, and I find on the water testing much more reliable than playing the guessing game in this area.

If I had the answer I would use it with my own builds, but I’m afraid it isn’t as straightforward as one might think. Keep us updated if you figure it out though. I’m sure you can find some material sink rate experiment online to give you a ballpark feel. Otherwise you can join the rest of us “cavemen” and learn by doing 

Yeah makes sense.  Fluid analysis is way above my intelligence level lol so I'm good with trial and error for that.

Also your advice about simplifying it to center of volume vs center of mass is really helpful.  I don't know why I was thinking I'd need to consider all the individual forces independently...so that gives me an easily obtainable goal so thanks!!!

[Brendan2468]

There are so many variables that you just have to accept you can not control during testing. So trial and error really is the best way of doing it, for me anyways, I have a good grasp on where weights needs to go and how much of it vs how much microballoons is needed to get the desired action and ROF. As Mike Bucca told me "There is no book or class you can take to learn all this, just trail and error." I think that is the best way too. If you just do what everyone else does when it comes to making baits there will not be much innovation and different ideas flowing. Finding your own path is pretty important in baitmaking, that is what will make you stand out from everyone else out there! Kinda off topic, kinda late just messin around lol cheers