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Marlin Tutorial


EAL Autopsy


It started innocently enough several years ago, with a cryptic message in the Home Office email inbox.

"You remember Deep Throat? Call me Blind Strike," the email began. "I can't tell you where I got it, and if you challenge me publicly, I'll deny I provided it. But once you see it, you'll know what it is."

With some trepidation, I opened the image file attached to the message:

At first, I had no idea what I was looking at. The grainy black-and-white photograph - could it be an X-ray? I looked closer ... the ghostly outlines began to arrange themselves into something familiar in my brain. "Oh my God," I thought. "It's an X-ray of an EAL!"

Stan's Tip

Before we begin, a disclaimer. Nothing in this article is an attempt to circumvent any proprietary material. SCMO has nothing but admiration for those who innovate our industry, and this is a clear example of innovation. None of the details herein are more than anyone with curiosity, tools and a $200 lure to sacrifice could discover for themselves. We're just saving you the grief ... :-)


The Beeper ... Ol' Chirpy ... Battery Pig ... Fish Magnet. Many names for the same marlin lure - the Electronic Acoustic Lure, or EAL. For the past half-dozen years, it's been the hottest thing going in the SoCal marlin scene. As a marlin fisherman, you buy (or rent) the lures, and feed them batteries - but how much do you really know about the EAL?

Our subject, blissfully unaware of its fate.

Over the years, many people have looked for new ways to fool a marlin into biting a piece of plastic. The Sonic EAL, introduced by Sevenstrand (now Pure Fishing) in 2001, wasn't the first to incorporate a noisemaker into the process, but it's the most sophisticated - and the most successful. Combining proven lure shapes with an electronic noisemaker, the EAL was immediately successful, in spite of a $200 price tag that caused many an angler to blanche. But the catch rate of the lure could not be denied, and soon no local marlin pattern was considered complete without at least one EAL in the mix.

Curious to hear what all the fuss is about? Just click here.

There are several stories on just how the EAL concept was developed. For a long time, Sevenstrand was understandably tightlipped about the technical details of the lure, and I can attest first hand to just how hard it was to get a straight answer out of President Bill Buchanan and Sales Manager Bill Goodman. Here's the official story from Sevenstrand:

"Many years ago we came upon a government study produced for the commercial fishing industry. It involved finding the sound frequencies made by distressed bait fish. The purpose of the study was to find out if a sound could be put in the water to attract game fish to a specific area. Based on this research we have put together various sound devices over the years, but the electronics have always been too large to fit into a lure. This is no longer true. With the help of an Aerospace Scientist with 20 years experience in the design of microwave and millimeter wave electronics we can now fit everything into a trolling lure."

It took over a decade to go from concept to prototype, but by 2001 the first EALs were given to elite marlin crews to test in Hawaii, California and Mexico. The results were immediate, and a legend was born. It was hard for many anglers, myself included, to believe the lure could be as successful as it appeared. After talking with several of the early testers, including Greg Stotesbury and Kenny Knight, it was clear that the EAL was real.

The EAL family portrait. Note all three share the same electronics subassembly.

The first mention of the EAL here at SCMO was a posting over at the Marlin Club back in August 2001. People were starting to hear the buzz (no pun) about the EAL and the success the prototypes were having. The lure hadn't been released to the general public, and the running gag was that you had to be an "FOB" or friend of Bob Hoose to get your hands on one. It was like watching a modern day Pied Piper whenever someone with EALs was in the fleet, as everyone tried to say the magic words that would lead to one being delivered via a plastic bag dropped into the wake.

The EAL comes in three sizes, but only the two smaller sizes are commonly used locally. The #3 is very similar in size to the old Sevenstrand Pro Series (or the new Pro Pusher #3), while #1 is smaller. I rig the EAL the same way I do my other lures, although there are those who advocate using wire leader, primarly as a way to protect the investment from the sharks that find the beeping irresistable. I don't personally advocate the wire leader method, fearing the wire will degrade the lures performace. As one EAL-trolling angler put it, "If you can't afford to lose the lure, don't run the lure".

Over the years, the EAL has established itself as an effective marlin catching lure. They continue to outperform other lures, and have demonstrated the ability to survive multiple marlin strikes without damaging the electronics. Clearly, the EAL isn't just a trend or a flash-in-the-pan.

The continued success of the EAL caused the Home Office staff to revisit the mysterious X-ray. I've picked up an EAL before and wondered what was inside - I know you have, too. So, in the name of scientific curiosity, a specimen from my colleciton was selected for sacrifice. I put on my goggles, lab coat and latex gloves and, doing my best Gil Grissom impression, began an autopsy of the EAL.

External Review

Our subject is a Sevenstrand Sonic EAL Electronic Acoustic Lure, size #3 in the black and purple color. The visible portion of the lure head is 1.5" in diameter and 2.25" in length, and the lure is at its full untrimmed skirt length of 11". There is visible damage to the head caused by marlin strikes; specifically, rasp striations in the hard resin head and a significant chip out of the leading edge of the head. It is this latter damage that ultimately led this particular lure to be selected for this project.

The head itself is made of hard clear resin and contains an cylindrical insert that fills all but the first third of the head. The insert appears to almost completly fill the circumference of the head; this could, however, be an optical illusion. The insert is pearly white with a prismatic effect; a seam is visible that would indicate it is a taped application. Two eyes are present on the sides of the insert in the form of Sevenstrand logos. The eyes are flat, unlike the three-dimensional ones present on other Sevenstrand lures. This leads me to believe the size of the insert leaves no room for anything but a sticker.

Feeling a wee bit nekkid?

We start by removing the skirts. There are two, each made of flexible plastic. The outer skirt is purple with blue flecks, while the inner is black with silver flecks. Both skirts are glued to the trailing portion of the head, but peel off easily.

With the skirts removed, we can begin our examination of the lure head. The head is much longer than that of a traditional marlin lure, with 2/3 of the overall length of 6.25" hidden within the skirts. The resin portion of the head ends at the attachment point for the skirts; after that, the size narrows down to a cylindrical shape with a consistent diameter of slightly over 1 inch. The cylinder appears to be coated with the same pearl white reflective tape as used in the head. However, the seam locations between the head and cylinder do not match, possibly indicating separate tape installations.

The posterior end of the lure head is potted with a clear resin, possibly the same material as used to form the head itself. There is a stainless steel threaded cylinder protruding from the resin, which is capped with a threaded plastic cap. Beneath the cap is a stainless steel plug that slips into the cylinder and is sealed with two o-rings. Removing this plug reveals the chamber for the 3v battery used to energize the electronics.

Directly above the battery cap is a clear plastic tube that runs the length of the head and exits the front of the head slightly above the centerline. This tube allows the lure's leader to pass through the head freely. Looking into the resin potting, what appears to be a hex-head setscrew is located to the left of the leader tube. There is also a blue compound present nearby, perhaps some kind of sealant used prior to the installation of the potting. The potting itself appears to be about a quarter-inch deep, although much like looking into water it is difficult to gauge the depth.

I next remove the reflective tape from posterior section of lure head. As we surmised earlier, the tape does not extend under resin forming the forward part of the head, indicating installation after resin hardening. The portion of the tube exposed by removing the tape is white in color, and feels like Teflon or a similar material.

Digging Deeper

Electronics subassembly.

A Dremel tool is used to remove the hard resin portion of the head. This is an incredibly messy operation, and that alone should make you happy it's me doing the autopsy and not you. Flaked polyester resin has the same reaction on bare skin as fiberglass - who knew?

With the resin removed, it is clear that the structure that makes up the cylinder of the rear of the head extends into the resin portion - the initial observation that it filled the resin head was simply an optical illusion. I remove the tape over the front section of the head (with eyes attached) to expose the remaining portion of the cylinder.

Once all of the decorative elements have been removed, we are down to the basic elements of the electronics unit. Looking at each of the other two sizes (the smaller #1 and larger #7), it appears that the same electronics unit is used in all three lures. This is probably the level at which Sevenstrand receives the subassembly from an outside vendor. It's also the reason the #1 EAL is so difficult to get to swim right - the diameter of the electronics unit forces the head to have a truncated conical shape that makes it want to plane across waves rather than dig into it.

Turning back to the electronics subassembly, it is a white tube capped at one end with the battery cap and resin potting described above. The front end is covered with an aluminum plug whose rounded edges blend smoothly into the main tube. I can see no purpose for going with the aluminum at this point other than appearance.

There is a noticeable weight differential that forces the tube to roll upright when placed on a flat surface. While this orientation does leave the battery case down, I don't believe there is enough weight in the case alone to cause this. There may be additional weights installed within the tube.

Heart Of The Matter

Insides exposed. Note the nose weight embedded in the forward potting, and dessicant bag behind circuit card.

Uncertain of the exact internal layout and not wanting to inadvertantly damage the electronics, I carefully carve a hole in the tube with the Dremel tool and remove a portion of the left side of the tube to expose the inside of the assembly. Once it is clear what can be removed without causing collateral damage, I remove approximately 2 inches of the sidewall of the assembly.

The inside of the tube, which is clearly PVC tubing (although probably not Schedule 40, as the walls are too thin), is hollow from the front plug to the rear. The inner wall of the rear cap is exposed to the interior of the assembly, and appears to have been installed using standard PVC cement (presumably this is the blue color we saw in the resin potting earlier). There appears to be additional resing potting material between the front of the internal chamber and the aluminum front cap. The clear plastic leader tube is visible running along the top of the chamber, with the battery holder directly below. The battery holder takes up approximately two-thirds of the length of the chamber, leaving the front third for the electronics.

Using the Dremel tool, I remove the remainder of the PVC tubing to expose the left side of the assembly from cap to cap. Behind the aluminum cap, which sits in a chamfer in the PVC tubing, is approximately 1 inch of resin potting. This potting holds a lead weight in place at the bottom of the assembly, which helps to keep the lure correctly oriented in the water and caused the assembly to rotate earlier. There is no evidence of glue holding the cap in place; presumably the resin provides this function.

Directly behind the resin potting, and in front of the battery chamber, is the heart of the assembly - the circuit card. It is a square, two-sided card measuring 11/16ths of an inch on each side. There are two wires attaching the circuit card assembly to the battery chamber. A blue wire runs from the card to the spring contact at the bottom of the battery chamber, passing through the insulated bottom of the chamber. The second wire, red in color, is soldered to a tab that is attached to the cylinder of the battery case.

Stan's Tip

Because the metal battery plug completes the electrical path for the circuit, it is very important that it be fully inserted and held in place with the plastic cap. The rubber o-rings will prevent the circuit from completing unless the shoulder on the plug makes contact with the outer edge of the battery chamber. If your EAL doesn't chirp, verify the plug is fully inserted and secured.

The smart part ...

... and the loud part.

The circuit card floats free in the space, secured only by the two wires connecting it to the battery. There is a bag of dessicant present in the cavity; this and the hex plug in the aft bulkhead leads me to believe the cavity was initially purged with an inert gas such as nitrogen prior to potting to prevent moisture buildup.

The card itself consists of a single integrated circuit and several discrete surface mount components on one side, and the sound producing element on the other. The IC is a dual timer/oscillator that provides the timing and input for the chirp element and controlled using the external resistors and capacitors that surround it. This is a good design feature, because it means that Sevenstrand can tune the sound frequency by changing the value of the discrete components without having to modify the circuit card design. In fact, several people have noticed different chirping frequencies over the years, which might indicate that the designers are making just such improvements.

Final Thoughts

I was one of those who was suspicious of the EAL when it first was released. I couldn't justify the high price tag, and refused to believe it worked as well as others claimed. However, as the results continued to pile up and I spoke with those who had achieved success using the EAL, I developed a respect for the lure and its designers, and became a believer. Now, having seen the inside of the lure, I have a better understanding of the research that goes into the EAL and the cost inherent in its manufacture. If anything, I have even more respect for those who developed it as a result of this experience. I've caught several marlin on the EAL, and until something better comes along, it'll have a place in my pattern.


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