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Trolling depth estimator

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  • Precision trolling crankbaits by mark romanack

    All crankbait trollers have one thing in common. They need to know how deep their favorite lures dive.

    Depth control is everything when trolling crankbaits. It doesn't take a rocket scientist to figure out that crankbaits won't catch walleyes, pike, trout, salmon and other species unless the lures are presented close to waiting fish. Little information on lure diving depth was available until recent years. Even most crankbait manufacturers didn't know how deep their lures would run.

    It wasn't until 1989 that noted walleye pro Mike McClelland stunned the tackle world when he introduced his book Crankbaits. A guide to trolling and casting depths of over 200 crankbaits, McClelland's trolling data soon proved to be a bench mark for anyone who fishes crankbaits.

    All of McClelland's trolling data was based on lures fished at or near their maximum diving depth. A trolling lead of 120 feet was chosen by McClelland. Reportedly this lead length delivered 90% of the maximum diving depth with lipped crankbaits.

    McClelland's data is backed up with reams of graph paper that show conclusively how deep various lures will run when trolled on 120 feet of line. Although McClelland's data was well received, the 98 cent question became, how deep will these lures run on shorter or longer leads?

    That question remained unanswered until a second book, Precision Trolling, researched and written by Michigan's Dr. Steve Holt, Tom Irwin and Mark Romanack took McClelland's data and crankbait trolling another step forward. The trio of anglers based their data on actual observation of lures pulled past a scuba diver.

    Each lure tested for the book Precision Trolling was pulled past a diver with 15, 30, 60, 90, 120, 150, 180, 200, 220 and 250 feet of line out. The depth ranges achieved using these leads were recorded and later plotted onto a graph the trio refer to as a dive curve. The dive curve clearly shows the downward diving angle for each crankbait, making it possible to quickly and accurately determine the exact lure diving depth for any lead length from 15 to 250-feet.

    Next Holt, Irwin and Romanack superimposed a life-sized picture of the lure onto a dive curve printed with easy to read "feet down" and "feet back" measurements. The life-size picture of the crankbait makes positive lure identification easy. Even if you don't know what brand or model of lure you're using, the bait can be quickly identified by comparing the lure photos on various dive curves.

    The dive curves are printed on heavy card stock. Connected together with a ring binder, the booklet is neatly bound and handy to use. Precision Trolling contains dive curves for 120 crankbaits including the most popular brands and models.

    All the testing and dive curve data in Precision Trolling is based on 10 pound test monofilament. Those anglers who troll using lighter or heavier monofilament line can still determine lure diving depth accurately by adding or subtracting diving depth depending on line diameter.

    "Those who troll with eight pound test line should add 10% to the depths listed in the dive curves," suggests Dr. Holt. "Those who fish 12 pound test should subtract 5%. Subtract 15% for lures trolled on 14 pound test and 25% for 17 pound test."

    For example, a lure that's running 20 feet on 10 pound test will run at 22 feet (20 ft plus 2 ft) on eight pound test, but only 15 feet (20 ft minus 5 ft) on 17 pound test line.

    Holt, Irwin and Romanack used Daiwa 27LC (line counter) reels to measure their lead lengths. "Each reel must be filled to capacity to get the most accurate readings," says Romanack. "A popular line counter reel, the 27LC reel holds up to 360 yards of 14 pound test monofilament. The 27LC holds enough line for most trolling applications. The exception to this rule occurs when fishing Dipsy Divers that require the larger 47LC model. The 47LC holds 280 yards of 20 pound test."


    Cranking Eyes Regardless of which line you select, monitoring trolling lead is a critical element of precision crankbait trolling. However, lead length is only one of several factors that determine how deep a crankbait will dive. Line diameter, the amount of line out and the shape, lip size and buoyancy of the lure all combine to determine maximum diving depths.

    The line diameter or pound test best for general trolling conditions is an often debated topic. Ideally a line suitable for trolling must be small enough in diameter to allow lures to dive deeply, while being strong enough to handle fish safely. According to Holt, Irwin and Romanack, 10 pound test is the ideal line when trolling for small to medium sized fish such as walleye, bass, brown trout and northern pike. "Lines smaller in diameter than 10 pound test have too much stretch making it tough to get solid hooksets," comments Irwin. "Small diameter lines also abrade more easily and may fail at the worst possible moment."

    "Lines larger than 10 pound test significantly reduce lure diving depth," claims Holt. "A 1/4 ounce Storm Hot 'N Tot maxes out it's dive curve at 15 feet on 10 pound test line. The same lure and lead combination fished on 17 pound test line will only dive to about 11 feet."

    When fishing for large fish like salmon, lake trout, steelhead or stripers, heavier pound test line is essential. "While heavier line reduces the diving depth of crankbaits, the loss in diving depth can be off set to a degree by letting out longer trolling leads," explains Romanack. "A compromise in line diameter is the logical solution to this dilemma. Try 14 to 17 pound test when fishing for salmon or other powerful fish.

    The amount of line let out is a strong influence on how deep a crankbait will dive. McClelland's book states that crankbaits will reach 90% or more of their maximum diving depth when 120 feet of lead is used. McClelland also claims that if too much line is let out the lure will actually lose depth because of excessive line drag in the water. The authors of Precision Trolling came to a different conclusion.

    "Every crankbait is an individual that has its own distinctive diving curve," says Holt. "Some lures reach their maximum diving depth with 120 foot leads, but many lures, especially deep divers are just getting warmed up at 120 feet." Holt, Irwin and Romanack experimented with lead lengths much longer than tested by McClelland. "In some cases we saw lures continuing to dive even after letting out 260 feet of line," claims Irwin. "The Luhr Jensen Powerdive Minnow is an excellent example. A lure with an extra large diving lip, the Powerdive achieved a depth of 25 feet with a 120 foot lead and 35 feet when trolled on a 260 foot lead."

    "The Powerdive minnow picks up an additional 10 feet of diving depth when run on very long leads," adds Holt. "A significant depth improvement, this lure and other super deep divers are capable of reaching greater depths than we ever dreamed possible."

    Ironically, not all big lipped lures turn out to be the deep divers they appear to be. The body size and buoyancy appears to have a major impact on how deep a lure will dive.

    "The Rebel D-30 Spoonbill is a good example of a lure I expected to be a super deep diver," comments Irwin. "After testing the Spoonbill D-30 and learning that it only dives to 18 feet, I was sure the lure tested had to be out of tune. After testing several other D-30 Spoonbills, I finally came to the conclusion that this bait which appears to be a deep diver is actually a medium depth diving lure."

    Large crankbaits with wide buoyant bodies tend to run slightly shallower than you might expect. Other big lipped lures that don't dive as deep as you might think include the Rapala No. 9 Shad Rap and Poe's Deadeye. Although each of these lures are excellent fish producers, they don't dive as deep as other lures with similar lip sizes.


    Precision Trolling It's a common misconception that trolling speed influences a crankbait's diving depth. It does not! Within the ranges of normal use, crankbaits will dive to the same depths regardless of lure speed. The exception of course are lures that are out of tune and not running properly.

    Holt, Irwin and Romanack discovered that lures trolled at .75 to 3 MPH all achieved the same maximum depth, but lures trolled slowly took a little longer for the baits to reach maximum depth.

    Trolling speed does however have a profound effect on lure action. Certain baits have little or no action at slow speeds and must be pulled at a brisk clip to be effective. Other baits simply can't be trolled fast or their subtle action is lost and the bait worthless.

    The best way to determine the ideal trolling speed for individual baits is to observe them running near the boat. Place the crankbait in the water and adjust the trolling speed until the lure responds with the best possible action. Make sure the bait is tuned properly and running straight through the water. If the lure wants to run left or right, the bait needs to be tuned by bending the line tie in the opposite direction.

    Tuning crankbaits is a tricky business. It takes patience and practice to determine the ideal action for each lure. Regardless of advertising claims, most brands and models of crankbaits need a little fine tuning to get the most action from each lure.

    Crankbaits run best when attached to the line using a small fast lock snap. Make sure the snap used doesn't include a swivel and be sure the snap is rounded in shape so the lure has a free range of movement.

    A polamar knot is the best way to attach a snap to monofilament fishing line. The strongest knot available and easy to tie, consult any package of fishing line for instructions on how to tie the polamar knot.

    Line bow while trolling is another factor worth exploring. "I noticed during many dives that most of the monofilament on a long lead floats on the surface," commented Holt. "With diving crankbaits, only the last few feet of line angles down sharply to the lure. When trolling, a large bow of line forms between the rod tip and the lure."

    Bow in the fishing line is a counter productive factor that makes it more difficult to hook fish while trolling. Before a fish that strikes a crankbait trolled on long leads can become hooked, the bow in the monofilament line must be pulled taunt.

    "There's no doubt that walleyes routinely strike at passing crankbaits, but before the line pulls tight enough to set the hook they sense something is wrong and drop the bait," claims Romanack. "No one knows for sure how much this phenomenon occurs, or how many fish willing to bite are not hooked each trolling season."

    There are several ways anglers can increase the odds of hooking the fish that bite. Trolling with the shortest leads possible helps to reduce the elapsed time between when a fish bites and the line pulls tight.

    Anglers can also try trolling a little faster than normal when the fish are biting well, but are not getting hooked up solidly. A faster trolling speed also reduces the amount of elapsed time between the strike and hookup and works to set the hook with more authority.

    Thirdly, using lines with a minimum amount of stretch is an advantage when trolling crankbaits. Wet monofilament line stretches like a rubber band, making it tough to set a hook solidly in the mouth of a walleye or other bony mouth fish.

    Certain types of monofilament are formulated for low stretch. A new line from Stren known as Sensor has the lowest stretch of any monofilament line. This outstanding line for trolling has about 50% less stretch making for better hooksets and a higher ratio of landed fish.

    Trolling with slightly heavier lines may also help reduce line stretch problems. Trolling with 12 pound test line reduces lure diving depth by approximately 5%, while significantly reducing line stretch problems associated with eight pound test line.

    "There's no perfect system that guarantees fish that bite a crankbait are going to get hooked and landed," admits Holt. "I put the odds in my favor by using the sharpest possible hooks. Thin round bend style treble hooks stick, penetrate and hold better than hooks made from larger wire. These hooks are also soft enough that they can be bent out and the lure retrieved if it snags bottom."

    The dive curve data prepared by Holt, Irwin and Romanack along with their fishing tips amount to a deadly system for trolling walleyes, pike, trout or any species that will strike a crankbait. "Crankbaits can be aimed at game fish that mark on a graph like a hunter aims his bullet," says Holt. "The secret to catching more fish is understanding how lead lengths influence lure depth and carefully putting your crankbaits where these trophies live."

    With Precision Trolling as a guide, crankbait trolling isn't such a mystery to the average angler. In fact, there are three easy steps to successful crankbait trolling.

    The first step is to locate fish with the help of your electronics. The second step requires the angler to select and try a variety of lures that will dive to the depths which correspond to fish marking on the graph. Patterning fish on crankbaits is as simple as selecting the proper lead length and seeing which baits the fish prefer.

    The final step is an important one that many anglers lose sight of. Once a productive lead length and lure combination are determined, it's critical to reproduce this combination exactly with other lines. Adding more lines with identical lures and lead lengths completes the pattern. When you've reached this point, it's all down hill. The hard part is over and it's time to reap the benefits of precision trolling.

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