# Bouyancy Help

## 8 posts in this topic

I am in the process of considering molding my jointed swimbaits. I came across a product that looks like it might fit the bill and it is local to me. My baits are made to sink so that is the intention. The product has a specific gravity of 1.05-1.09 the manufacturer did not have the info on hand to give a specific number. I am not competent enough in the mathematics of bouyancy to know how fast this product might sink. Can someone give me an idead of how fast a rate of sink would be with this number? Again I want the bait to sink, but when I add all of the components I cannot have it sink like a rock. BTW most of my baits are fished in salt water so the rate of sink compared to fresh water is noticably slower.

Thanks for the help.

DaveB.

KelpKritter

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K/K what's the product, maybe someone has already gone down this track? - To get your buoyancy back do the opposite to ballasting, drill some largish holes in the TOP and cap them, has exactly the opposite result to adding lead. In fact if you are moulding them you could maybe add some styrene balls to the top of the mould cavity. pete

Edited by hazmail

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Weigh your current bait with just the current blank without hardware/lip/etc. From that you can compare the specific gravity. Alternately, you could simply look up the specific gravity of the wood you are using. Remember that even if weight of finished bait is equal, weight distribution will change the center of ballast and moment arms, so action may well change. This could be good or bad of course.

Dave probally could help ya more..

Clemmy

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I found a web site with some simple calculations, which I played with. Not sure how realistic the answers will be, because body shape is not considered in these calcs.

density 1.05 : fresh water = 1.6ft/sec : sea water = 0.8ft/sec

density 1.09 : fresh water = 2.9ft/sec : sea water = 2.0ft/sec

These sink rate numbers will increase when the hardware and epoxy are added. I did calcs for this too, but the sink rates seemed unrealistically high (6ft/sec), so I suspect an error in my work.

The above figures seem realistic, comparing with a lump of polyester resin (density 1.2) dropped in water, which sinks very fast, too fast to get an estimate unless you have a 6 foot bucket.

Dave

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The product is by AeroMarine and can be found at www.jgreer.com.

Thanks for the replys thus far.

Dave if the 1.05 number is accurate then I would simply need to cut down my weight which is easy enough to do and I would probably be right about where I would want to be. Thanks for the calculations.

I am sure with some trial and error I could also figure a ratio of microballoons to add to the mix to get what I need, but I was hoping I could avoid that since I am desiring a sinking lure anyways.

DaveB.

KelpKritter

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The product is by AeroMarine and can be found at www.jgreer.com.

Thanks for the replys thus far.

Dave if the 1.05 number is accurate then I would simply need to cut down my weight which is easy enough to do and I would probably be right about where I would want to be. Thanks for the calculations.

I am sure with some trial and error I could also figure a ratio of microballoons to add to the mix to get what I need, but I was hoping I could avoid that since I am desiring a sinking lure anyways.

DaveB.

KelpKritter

Dave,

I would be careful about removing lower ballast weight to achieve buoyancy. You'll sacrifice stability, and get rolling.

I'd try to get a floater with no ballast, so I could add belly weight to make sure the lure swims right.

Pete's idea is a good one. Some through holes up high, capped with beer can cutouts, to form air pockets, if your rate of fall is too fast.

But I think you can play around with the microballoons and get a blank that's almost neutral, or even floating, like the PVC blanks, so you can fine tune them with added ballast. Once you get one right, you can modify your mould to add the ballast holes in the casting, and make it easier to add the weight.

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Mark,

The bait swims virtually the same whether I use the weight that is currently in the bait or if I cut it in half, which I could conceivably do based on the information I have now. Now that could all change with a change in the material, but I wanted to narrow the options for materials I have been looking at.

BTW you have a PM concerning the AZEK.

DaveB.

KelpKritter

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Ive been using that kind of product for a while now and it is very differant from wood. Mark is right it is best to make it float then sink with ballast. Or like me you might get a surfing action(on the largest surface area). I changed from wood to resin about 3 mo ago and am still working out the bugs in my casting skills. But the action is definatly not the same as wood. By the way the stuff you are looking at is real close to what I got from tap plastics. The molds seem to be the most important thing though.