Factors affecting lure depth
1. Bib design
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 by replacing hooks
with larger (heavier) ones. But if you overdo it, you make kill the action.
4. SpeedWithin limits, a faster retrieve speed will send a lure deeper. Go too fast, though, and it will surface and blow out.
5. Line length
Within limits, the more line you have out, the deeper your lure can dive. However, water resistance against the line will limit the ultimate depth attainable. With a very long length of line out, while trolling, for example, water resistance will place upward pressure on the fishing line and defeat the lure's attempts to dive deeper.
You don't believe it? :-) That's understandable. Most everyone's logical, initial assumption is that the more line we have out, the deeper the 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 lure on your line. You lower the lure to the bottom. It stays there, 100 metres down. Like a stone!
Now, put the boat into gear and start trolling. Instead of going straight down, your line will start to stream out at a low angle behind the boat. What is making it rise? Water resistance to the forward movement of the line itself.
When the line stops rising, you may find, for example, that the lure is running 3 metres under the surface, 100 metres back from the boat.
You may also find, for example, that the same lure runs 3 metres below the surface when trolled only 20 metres behind the boat. At 15 metres behind in may be running 2.5 metres under.
There is a point where letting extra line out gives you no extra advantage,
other than distancing the lure from the noise of the boat. Which is fine,
if that's your objective.
6. Line class (diameter)
Lures can dive deeper on smaller diameter line that have 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 have been a boon to anglers seekin greater depth with their crankbaits.