Body Roll

[Ishitaro]

I am building a 7" Cigar minnow and just tested it and noticed it had too much body roll. The swimbait is a 4 section "V" notched swimbait including the tail. I have the ballast in the 1st ,2nd, and 3rd sections. I predrilled the ballast holes while it was still a block so there shouldn't be an issue with having them lined up. The front section is weighed more to sink head first which it does, but I'm thinking the weight in the 3rd section is throwing it off, If I take it out then it won't sink. I noticed that when I burn it through the water the body roll goes away. The only thing I can think of is the height of the swimbait is relativly short in comparison to the COG. Also, I did not test it with any hooks and I know this could effect the body roll. I will try that next.

Any comments or suggestions are welcome and thanks in advance.

 

The test was also to see how the tail effected the way it swam. It swam much better without the tail needless to say. I'm thinking the tail section is too long. I would like to have a tail on it obviously but hate that it acts like a rudder. Again, any comments or suggestions are welcome.

 

 

Mel

[mark poulson]

Ishi,

I find that rounder bodies tend to roll more.

I make my swimbaits with flat, tapered sides.  They are tall and thin.  I make them from 1"+- PVC decking.

They generally start out 7/8" thick at the back, and then about a third of the way down, I start my taper, so the belly is 5/8".  This still leaves plenty of room for ballast and hardware, but I find the flatter sides reduces roll, and the V cross section lets me burn them without roll at high speeds.

You bait looks almost round, so it has a lot of buoyancy to overcome to get it to sink.  If you flatten and taper the sides, you will remove some of it's buoyancy, and should be able to remove the ballast in the rear section, or at least reduce the amount of ballast you need to get it to sink.

I hope this helps.

[Ishitaro]

Thanks for the feedback Mark. It's a slight tear drop shape. But your right, my last 2 swimbaits had flatter sides and swam great with little to no body roll. There's so many things to remember when designing a new swimbait. I'll flatten the sides, reduce the 3rd section ballast and test it with some hooks this time. I'll let you guys know how the test goes. Thanks again!

 

Mel

[atlasstone]

I had the same issue with a crankbait design I had and through my research I found that a good understanding of stability really helps.  The center of gravity is where I started looking but found that the relationship between the center of gravity, the center of buoyancy, the metacenter and the impact they have on the overall stability helped me understand how to tighten, loosen or remove the roll of a bait.

 

Here are a couple links if you are interested:

 

This is where I started - http://www.planetseed.com/node/41133

This one has several pages and it goes through buoyancy, stability, COG, COB, metacenter etc. - http://www.cruisingonstrider.us/Buoyancy.htm

[Vodkaman]

Atlasstone - great links, especially the second. The guy has a talent for explaining, something that I struggle with.

 

I too have done a lot of work with CoB and CoG, using CAD models. This work was particularly useful for predicting the rest or static angle of the crank bait. The drawing shows how the CoG moves as each element of the lure is added.

 

As far as swimbaits are concerned, the aim is to have the CoG directly below the CoB, so that the lure sits in the water and swims horizontally. You would think that maximizing the distance between the CoG and CoB would give the maximum stability against roll, but I discovered that there was a lot more to preventing roll than this.

 

After building and video of about ten variations of hinge types and ballast locations, I never really cracked the problem. I was more interested in reducing nose side movement, but this is inherently connected to roll.

 

Personally, I think that the biggest contributor to swimbait roll, is not having ballast in all the sections, especially the rear sections.

 

Explanation - As the tail swings out to the side, the un-ballasted section is applying an upwards force, causing a rotation. The wider the tail section swings, the more rotation force is applied. It is a force x distance thing.

 

Take a look at

, especially from 52s to the end, the under water sequence. It is a difficult question - is the roll coming from the water forces at the front end or from the buoyancy of the rear segments - probably a combination of both.

 

Still a lot of work to be done before we fully understand swimbaits.

 

Dave

[kajay920]

Very interesting. Would a dorsal fin help prevent the roll or would it just inhibit the S action?

[Ishitaro]

Thanks for posting the links Atlasstone that put the COG in perspective very clearly.

 

Ok, so I tapered the sides to where they are flatter and added hooks for this test and it tamped the body roll a little, but it's still there. Now that I think about it that makes a lot of sense with what Vodkaman is saying about the tail section not having a ballast. I was also thinking about backing out the screw eyes a little to give the joints a little more play, but I don't think it will make a huge difference. I'll make the changes and keep you guys posted. Again, thanks for the suggestions and feedback.

 

Mel

[Ishitaro]

I drilled all of the ballast holes vertically vs horizontally making the ballast closer to the COG. Like Vodkaman said the goal is to maximize the distance between the CoG and the CoB, so I will also make this change and let you guys know how she swims. Before you know it this swimbait is going to look like swiss cheese.

 

Mel

[atlasstone]

My theory is much like Vodkaman's in that the CoG needs to be below the CoB to maximize stability.  It doesn't necessarily remove the roll, but it does help.  This explains why taller baits tend to be more stable and shorter baits roll more.  Much in the same way that flat sided crankbaits tend have a tighter action but rounded ones have a wider wobble.  Here is how I view stability in swimbaits (no making fun of my drawing):

 

 

With that in mind, here is my theory on rolling.  While at rest, all is good, but when it moves, there are several things going on.  The distance between the front and back of the bait will grow and shrink as the side to side movement is created.  This has a slight effect on the side to side stability as the "footprint" moves back and forth across the center line.  Assuming that the ballast is mainly in the middle section, the weight will move away from the center line, which acts as an axel, causing the bait's middle to drop.  As it moves back to center, it stabilizes and then the imbalance shifts to the opposing side.  Here is another poor drawing of what i am talking about:

Assuming this makes sense, to Vodkaman's point, it is more than just stability as far as the roll is concerned, but stability certainly helps as it takes more force to pull it off balance and makes it quicker to stabilize at the center.  If the movement of the weight across the center line causes roll, then to build on Vodkaman's theory, it would stand to reason that the roll might be reduced if the ballast was greater in the front and rear sections with just enough to stabilize the middle to decrease the amount of weight moving off center.  That's just a guess though as I'm sure there could be other impacts to the action.

 

hope this helps!

[mark poulson]

I am no engineer, so what I know about swimbaits comes from building them.  Trial and error.

In hindsight, here's what I've learned.

Way back when, Dave posted some interesting info on votices, the effect of water passing over and around lures.

With that in mind, I came to the conclusion that the flatter sides made more prominent vortices along the sides of the swimbait, which encouraged less roll and more stability.  The more round the sides, the more evenly the water flowed around the bait, and the more easily it would roll side to side.

I tapered my swimbaits because I was trying to remove buoyancy from the belly without altering the shape too much, to encourage stability at higher speeds.  It worked.

Even a blind pig finds an acorn once in a while.

[Vodkaman]

Mark - theorizing is fine, but I have to say that I probably learn more from building and testing. Theory gives me a place to start the search for answers.

 

Dave

[mark poulson]

Mark - theorizing is fine, but I have to say that I probably learn more from building and testing. Theory gives me a place to start the search for answers.

 

Dave

Dave, I agree, theoretically.  Hahaha

[BigRockPlugs]

You didnt mention what kind of wood you used. Try heavy hard wood for the front section and go lighter as you go back. Make sure you "grain" the front section, meaning put the heaviest grain on the bottom of the body. then weight it after you assemble it, at least for the first one. Also don't weight any of the middle sections, just thwe front and the tail if you need it.

Edited March 18, 2013 by BigRockPlugs

[Ishitaro]

I appreciate everyone's help on this build as it has not been easy to eliminate the body roll. I used PVC and the bait measures 7" in length and is 1 3/8" tall.

 

This is what I have done so far and what the results were.

 

Test #2: Tapered sides to be more flat and and removed 3rd ballast weight and tested with hooks this time. Results- Still had body roll, but sank at a faster rate. Body roll subsided when burned through the water.

 

Test #3: Removed old ballast weights and installed horizontally and flattened, maximizing the distance from the CoG. The first ballast weights were inserted vertically and almost touched the CoG. Results- The changes made a signifigant difference to the body roll, but still exist.

 

I belieive with this particular bait there is not enough distance from the CoG to the bottom to fully eliminate the body roll, afterall I'm only dealing with 11/16" from to the CoG. I will continue through trial and error to be body roll free and let you guys know if I have any success.

 

Again, thanks for all the help and support on this build.

 

Mel

[Vodkaman]

Ishitaro - excellent feedback on your tests. I just wish everyone who receives answers and advice would come back and tell us the results, this way everyone learns something, including the people handing out advice.

 

Dave

[Ishitaro]

Ok, so not settling for failure I examined my bait a little further and decided to taper the bait a little more, this time from front to back. Also, I added a small ballast weight in the fourth section as Vodkaman had theorized and Viola! Success at last, it even has little to no head shake. So, at this point I can't pin point if it was the weight in the last section or tapering it from the front to the back. I took a short video I will try to post up. Again, big thanks to all that helped!

 

Mel

[Vodkaman]

Ishitaro - Congratulations on a successful result. Pity you didn't test the ideas one at a time, but at least we have the solution nailed down to only two changes.

 

If the solution does turn out to be the weight distribution, this will be one-up for theorizing

 

Dave

[Ishitaro]

Actually I did perform a video test after each change I made, but can't figure out how to post them on here.

 

Mel

[kajay920]

Actually I did perform a video test after each change I made, but can't figure out how to post them on here.

 

Mel

Mel,

    In the bottom right of where you are posting is the More Reply Options buttons. A new screen pops up and on the bottom left is the Choose Files button. You should be able to click on that and Browse to your video file. 

Good luck

[Nathan]

You might want to post them on UTube then post the link here...Nathan

[Vodkaman]

What Nathan said, a Youtube link is the way to go.

 

Looking forward to seeing the vids.

 

Dave

[Ishitaro]

Thanks for the help guys.

 

I thought I had more video's, but apparently not. Sorry for the shotty video footage I was by myself and only had my phone to record.

 

 

 

This is how it swam originally with a tear drop shape, vertical ballast in the 1st, 2nd, and third sections. You can clearly see the body roll so bad that you can even see the hook hangers.

 

 

 

 

 

In this clip I tapered the swimbait more from the front to the back, as well as, from the top to bottom and included a ballast weight in all sections. I'm happy with the way it turned out with very little body roll and little to no head shake.

 

 

Thanks again!

[Vodkaman]

The first video is set to private. You need to go into edit and change the setting.

 

The second video is terrific, hardly any roll and zero head shake. Great result.

 

Dave

[Ishitaro]

Let's try this again.

 

[Vodkaman]

Yes, that works.

 

The two videos really demonstrate a massive improvement and how finnicky lure design can be.

 

Dave