When lake trolling you get frustrated a lot because you cannot keep your lure in front of the fish. You crank up your speed and pay out line. You watch the rod tip dancing back and forth and know you’re twenty feet or more outside the strike zone. Not bad luck. Physics. And guess what? You control it. If you measure instead of just guess, you control it.
People treat a jet diver like basic sinker, they don’t realize it’s a hydrodynamic wing. They don’t understand it. That’s why they don’t use it right.
How to Control Diving Depth
Planer Similar to a water ski, it plans across the water’s surface. A diving vane and wire lip produce downward thrust on the water. This thrust reacts against the water’s pressure, creating a predictable diving depth as diagrammed in infographic above.
You might assume that paying out more line means you’ll go deeper. That’s true but that’s only one part of equation. The other piece is speed. For example, if you were to increase your trolling speed from two to four miles per hour with three-hundred feet of line out, the diver doesn’t simply maintain its depth. In fact, it rise considerably towards surface.
The chart makes the opposite relationship obvious. Less forward drag (slower speeds) results in deeper dives since the vane’s downward angle have less resistance. Because of this, a GPS speedometer is always necessary. Wind and current will cause most boat speedometer to lie and that 1/2 mile per hour can swing your presentation 10 feet. It is the difference between a full cooler and an empty one.
Diver sizes are less about personal preference then they are about finding the correct size for the thermal layer where your targeted species are located. The chart indicates a Size 20 is ideal for shallow presentations. For example, this would be common during early spring applications for steelhead or walleye hugging the upper two dozen feet of water column.
When targeting Chinook salmon in July, however, those fish are typically buried in cold water close to the bottom. This is where the big boys come into play. The larger Size 40 diver is designed to do the heavy lifting for these uses. At slow speeds with long line payouts, it will dive well past one-hundred-fifty feet. Just as you wouldn’t use a drill bit to dig a hole in deep water, don’t expect a shallow diver to reach down into thermocline.
The logic is further supported by the infographic’s species guide that pairs each fish behavior with appropriate tackle. For instance, Coho salmon are typically mid-water aggressive feeders, making a versatile Size 30 the best option most days.
Another thing that confuses beginners regularly is line type. These charts are based off standard monofilament line with its drag and lots of stretch. Change to something like lead core or braid and you’ll want to tweak your expectations. Because braid is much thinner in diameter, it’s going to create less drag and resistance against the water. It will pull the diver deeper than what the chart indicates. Likewise, the additional weight carried by the line itself is even more noticeable with lead core. Without taking this into consideration, you can suddenly be digging into bottom when you didn’t expect to.
It is not a defect of your equipment. Just physics that demands our respect. Too many people pay out four hundred feet of braid thinking they’ll get the same results they would of using four hundred feet of mono. That doesn’t work either. Slow the boat down, shorten the line or add some drag to make up for how much more efficient the thin line is.
Memorize all those numbers? That’s not the trick. It must be repeatable. Next time your boat catches a fish note the exact line counter readout and your GPS speed. Every time. Soon you’ll have your own personalized table that outperforms any generic guide. We tend to view fishing as more of an art than a science, but depth control isn’t; it’s a science. Get the math right and the rest will take care of itself.
And lastly, stop wondering where your lure is located, know where it’s located. Those fish aren’t hiding; they’re waiting at a certain depth. You simply need to arrive there consistently.