Factors affecting fishing lure depth
1. Bib design
Similar to 'action', the diving ability of a Predatek fishing lure is mainly determined by the shape, size and angle of attack of the plastic bib and the relative position of the tow-point (the eyelet or steel plate to which the fishing line is attached).
Other factors do, however, come into play.
Naturally, sinking lures go as deep as you allow them to sink. If you have two floating lures with identical bib configuration and body size, the heavier one will go deeper.
You can increase the diving ability of a crankbait fishing lure by replacing hooks with larger (heavier) ones and using heavier terminal tackle (wire snaps or swivels). But if you overdo it, you may kill the action. It's a matter of balance.
Within limits, a faster retrieve speed will send a fishing lure deeper. Go too fast, though, and it will surface and blow out.
5. Line diameter
Lures can dive deeper on smaller diameter line that has less resistance when drawn through the water. Using an excessively heavy line class for the chosen lure will reduce its performance.
The fine diameter gel spun lines of recent years has been a boon to anglers seeking greater depth with their crankbait fishing lures. Another benefit of no-stretch gel-spun lines is that they transmit the vibrations of the fishing lure's action back to the rod tip more effectively than monofilament lines.
6. Line length
Within limits, the more line you have out, the deeper your fishing lure can dive. However, water resistance against the line will limit the ultimate depth attainable. With a lot of line out, while trolling, for example, water resistance will place upward pressure on the fishing line and defeat the fishing lure's attempts to dive deeper.
You don't believe it? :-) That's understandable. Most people's logical, initial assumption is that the more line we have out, the deeper the fishing lure can go. But think of it this way...
You're in a stationary boat, in 100 metres of water. You have a small, slow-sinking fishing lure on your line. You lower the lure to the bottom. It stays there, 100 metres down—hanging like a stone on the end of the line.
Now, put the boat into gear and start trolling. Instead of going straight down, your line will start to stream out at an angle behind the boat. What is making it rise? Water resistance to the forward movement of the line itself forces the line toward the surface. The same thing will happen even if you have nothing on the end of the line but a lead sinker.
When the line stops rising, it's because the diving force of the fishing lure matches the opposing water resistance forcing the line toward the surface. You may find, for example, that the lure is running 3 metres under the surface, 100 metres back from the boat. Increasing the length of line to 200m will not necessarily allow the lure to dive deeper.
You may also find, for example, that the same fishing lure runs 3 metres below the surface when trolled only 20 metres behind the boat. At 15 metres behind it may be running 2.5 metres under.
It's a case of diminishing returns. There is a point where letting extra line out gives you no further advantage, other than distancing the lure from the noise of the boat—which is fine, if that's your objective. :-)