I have been fishing for bass most of my 64 years, but while "adding some lead weight" to some jerkbaits in an ice chest full of water in preparation for some wintertime bass fishing I decided to check some of my co-poly line (McCoy and P-Line CXX) to see if they would sink or float.  I just cut a few 6" lengths of line and dropped them in the water.  I was pleased to find they sunk at about the same rate as some fluoro line I tried as well.  Now here is the kicker - I did the same with a couple of well known monofilament lines that I had handy.  They also sunk!  The only line that did not sink was braided.  I have always avoided mono line for deeper crankbait and weighted plastics because "mono does not sink."  This was a very simple experiment and there is probably a very basic explanation for the mono line sinking.  I look forward to hearing from one or more of our line guru's at this great site for an explanation.  Thanks.

Most lines will sink with the exception to braid once the surface tension has been broken.    Did you lightly set the line in the water or just let it splash down from a distance? 

 

Also most mono and copoly in most cases sink at a slower rate than fluorocarbon and leaves a bow in the line which impacts the lines sensitivity and ability of crankbaits to pull the line down to help it dive. (Water temp, amount of line out, line density, ect will depict how fast a line will sink)  A crankbait will actually dive deeper with 10lb braid than 10lb fluoro or 10lb mono because its diameter is smaller allowing the bait to pull the line down easier. 

 

Too many variables for me to give an accurate answer but this is my opinion on this.  I say if you like the line for a particular technique stick to it and don't switch because someone says this or that because their style of fishing may be different than yours.  A good example of this is Rick Clunn.  The guy fishes crankbaits with mono exclusively where everyone one else fishes with fluoro.  Y?  Because of how he works the bait and his particular setups.

Next KVD, I accounted for the surface tension issue by holding the line slightly under water before allowing the line to float to the surface or sink to the bottom.  Your comment that "most lines will sink" is the explanation (fact) I was looking for.  I was expecting the mono to behave more like braid relative to floatation.  It appears that line diameter is a greater factor than line composition when it comes to various applications.  Thanks for the explanation.