How to

How Deep is Deep?

The quest for lures that get down deep is one that all anglers are familiar with. Bushy explains a few tips to help you get down to where those really big fish live …


“I WANT a barra lure that has a nice action, casts straight and goes down to about 100 feet on a good cast.” Of course, this would be a pretty stupid request from any tackle shop customer, but having been behind the counter of a few shops I know how unrealistic the expectations of some customers can be. Maybe as fishos we have all been spoon fed for too long and we just expect things to be black and white. After all, it’s easy to know exactly how deep any hard-bodied deep diving lure goes because it is generally written as plain as day on the packet. And if it is written on the packet, it must be right. Right? Well, sort of.

Question: How deep does a deep diving hard-bodied lure actually go? Answer: How long is a piece of string?

Sorry for speaking in riddles like some sort of Shaolin monk instructing a “grasshopper” in the finer points of some obscure martial art, but the depth a floating lure with a bib can achieve in an actual fishing situation can only be determined by a very complicated mathematical formula. Some of the parameters that have to be included in the equation are quite tricky. Is the lure being trolled or cast? If it is being trolled you have to take into consideration the length of line that is between the rod tip and
the lure. As the length of line increases the lure will travel deeper and deeper until there is a point where the water drag on the line balances the pull of the bib and then the lure just won’t go any deeper no matter how much line you let out. The diameter of the line is also very important – as the diameter of the line decreases, any lure trolled will go deeper. This is also true for leader diameter – thinner leaders will allow greater lure depth and fatter ones will restrict the lure’s ability to dive. Speed is also a factor to consider as any lure will have an optimum speed that gives it maximum depth. This speed may, or may not, be the speed that causes a fish to bite it!

If the lure is cast rather than trolled, the same laws of physics apply, but casting distance becomes important. Generally it is fairly difficult, or if we are going to be fair dinkum, just about impossible, to cast a diving lure far enough for it to go as deep as a trolled lure.

So what does the depth marked on a lure box actually mean and how has the manufacturer arrived at that particular rating? The answer to that question probably varies with each manufacturer. If you want to make your lure appear to
be a world beater you could troll it on very fine line at its absolute optimum speed and depth, and then stamp the truthful depth on the packet. This is probably what some makers do and that’s fair enough. The only drawback I can see to that method is that some customers might be a bit disappointed if they can’t match the stamped depth when they rig their lures with fishing leaders and the diameter of line they want to use for actually catching fish.

On the lures I design I’ve opted to go the other way and nominate a depth that can be achieved when the lure is rigged with lines and leaders that will be used in an actual fishing situation. You just have to bear in mind when buying any lure that the depth rating printed on the packet can only ever be a guide, and the actual depth you will personally achieve with the lure will depend on how it is rigged, cast, trolled or retrieved.

Floating deep divers are great fun to fish and you can certainly enhance their depth range by keeping your lines and leaders as fine as possible and by casting them as far as you can. In a practical sense, however, I have found that keeping most of these lures below a genuine 10 feet and targeting the fish that live below that depth with them is just not worth persevering with.

Below 10 feet, sinking lures just work too well to keep on with the floaters. Soft plastics have now invaded many of our fisheries and one of the reasons they have is that it is just too easy to fish them in water between 10 feet and the bottom. It’s dead easy to fish the plastics in the deep because we just have to play around with the weight of the jig heads we’re using to control the sink rates. It’s possible to vary a jig head weight to rig a lure to plummet straight to the bottom or to go a bit lighter and to fish the same lure slowly through the water column. No more struggling for depth.

If you want to fish the bottom it doesn’t matter how deep or shallow the water is, a vibrating blade lure will probably do the job effectively. These lures will fish within a metre of the bottom and do it all day every day with minimum effort.

The Bushy depth theory seems to work well enough on some of our more popular fisheries – bass, barra and bream all feed from top to bottom and when the going gets tough for floating diving lures at about 10 feet, the plastics and vibes come into their own.

Even if you get a few fish with the 10 foot rule it would be a shame to let the guys who work in tackle stores off the hook entirely – I think some of us should take it on our shoulders to make sure the question still gets asked. “Got any barra lures that float and then dive to about a hundred feet?”

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