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Depth Finders
By Paul Crawford

There is no piece of gear serious fishermen use which generate more opinions and controversies than depth finders. Some folks couldn't even go to the lake without a depth finder while others have three on their boats and never turn them on. Features and brands are subjects for constant debate while the majority simply turn on their depth finders in Automatic and never access the features they paid for. If you happen to be in the market for a new depth finder, matters get even more confusing because of the claims and counter claims of the manufacturers. I happen to be in the market for a new depth finder and did some research into the new offerings for 97. I thought I'd share with you what the Marketing Departments told me, what the engineers said it meant, and, as always, add a liberal dose of my own opinions of what was really worth it. Even if you're not in the market for a new depth finder right now, maybe you can pick up some new tricks and it's always nice to keep up with what's available.

The two brands I chose to investigate were the Hummingbird lines and the Eagle/Lowrance lines. There are other companies out there which make depth finders of various quality, but we have about an 85% of market share between these two lines. If nothing else, it gives you something with which to compare another manufacturer.


This is the real business end of any depth finder and what ultimately determines what, and how well use see into the underwater world. When comparing transducers, you need to look at cone angle, frequency, and to a lesser degree, power or signal amplitude.

Cone Angle is a standardized measurement indicating the average distance across the bottom the unit considers valid at any depth. Cone angle is normally measured at 50% full power (-3db). The standard cone angle offered for freshwater use is 15 to 20 degrees which means you are seeing the average of a circle on the bottom just a bit less in diameter than the depth of the water, (26.5 degrees would be the same). What you want in cone angle largely depends on what you are looking for. If you are looking for depth changes or other bottom structures, a narrow cone angle will give you the most up to date readings since the area average is less. The penalty is you will miss near cover such as weeds, stumps, or brush because you have limited your search area. For finding cover, or fish, you'd like with widest cone angle to cover the most area, but will, of course, sacrifice those quicker update on depth. The 20 degree compromise is actually a very good one in water under 60 feet deep or so.

Frequency is another trade off. Frequency measures the elapsed time between pulses, and therefore, determines the update rates. The higher the frequency, the more detail you can see. The problem high frequencies is they reflect too good, so you loose penetration and distance. The reason you have to worry about penetration is if you are just bouncing off the first thing there, how will you know the difference between a hump and a clump of weeds? If you have too high of frequency, and happen to be setting on a weed bed 4 feet high in 10 feet of water, for all you'll know it's just 6 feet deep. On the other hand, if the frequency is too low, it may actually go right through the weeds and muck and tell you that you're in 12 feet with no cover at all!

Power is the most overrated of the specifications. Both Lowrance and Hummingbird units use 600 watts peak to peak, (75 watts RMS if you care). This is more than adequate for depths under 100 feet without any real signal loss. I've see ads for other manufacturers that stress how much power they use, and if I was in saltwater in 500 feet, I might care. Personally, I've never caught a bass below 100 feet.

Lowrance and Eagle units come with a standard 20 degree cone angle, 192 Khz transducer. When combined with their Advanced Signal Processing, (filtering, Pulse Width Modulation, with Gain and Level equalization), they claim they will pick up cover and fish at 60 degrees or more. Not an unreasonable claim, but you will need to be under perfect conditions to actually get those kinds of readings. Their transducer is a good compromise between detail and penetration working well to at least 300 feet. For deep water applications, they also offer an 8 degree transducer that puts at a 50 Khz signal at a whopping 3,000 watts. That will easily give you bottom readings in over 1,000 feet. Their top of the line Lowrance X85 unit has a special transducer that is a combination of both their 8 degree and 20 degree transducers in a single package with automatic change over.

Hummingbird has gone to 16 degree cone angle yet are working hard to locate suspended fish. They up their frequency to 200 Khz offering a bit more detail at the cost of bottom penetration. With their version of Digital Signal Processing, they claim an effective 45 degrees of target recognition or about the same 3x as Lowrance claims. But they are also big in area coverage, so they have a cute way to show you suspended targets without loosing bottom accuracy. In their 2 and 3 beam transducers, they put out a 455 Khz signal to either side, using it to locate suspending fish without really get much of a bottom return at all. They claim they now can cover up to an effective 90 degree cone angle, or everything down there. Well, that may be a stretch, but it should work up to a point. The immediate trouble you get into with that much information is how to display it on a moving graph. Their solution is to give you 3 types of fish symbols, a solid black one that represents what you'd see with the normal 16 degree transducer, an outline of the symbol facing right for those fish on the right side of the boat, and an outline of the symbol facing left for fish on the left side of the boat. Neat, Huh? Well.... let's move on.


For most people, the display is single most important feature on a depth finder. For 97, both manufacturers are taking things to a new level in their top of line models. The "moderate" price units have inherited the top of the line displays from last year, and the "low" price units get the moderate displays.

On the top end, both manufacturers have turned to the new Film SuperTwist Displays, (FSTDs), and now offer 240 vertical pixels. This is state of the art stuff and finally even exceeds the resolution of the paper graph machines in an electronic display. You're also into 4 gray levels instead of the traditional black and white. The contrast is enhanced, and with improved backlighting, can be seen at night better than anything previously offered. It's not quite Television quality yet, but it's close. The Eagle Optima and Lowrance X75 and X85 have a 240 x 240 display. The Hummingbird Paramount is a 240 x 320 for those fans of long history and wide screens.

In the moderate priced units, Lowrance offers the X65 and Eagle Ultima Classic. These have 160 x 160 displays, the same as last year's Lowrance X70A. This is still pretty good stuff and you'd be hard pressed to tell the difference between the top of the line and these units under most conditions. Hummingbird has finally answered with it's Panorama offering a 136 vertical x 160 display. This unit also has Hummingbird's GRAPHLOOK which is bottom hardness indication to answer Lowrance's GRAYLINE.

About the only entry in the "lower" priced units announced so far is Hummingbird's Portrait. This has most of the features of the higher priced units with a 128 x 128 display. Before we turn up our noses at this display we need to remember it was a top of the line only 3 years ago. The Portrait is positioned to compete with Lowrance's X25 and Eagle Magna III line that debuted last year.

Features in Common

The following list are features that both manufacturers share in their product lines. They make a big deal out of them in their product literature, but they are things you would expect in any high quality unit.

Manual Sensitivity - The one feature every unit has, and probably the most under utilized control on the box. The Automatic setting is just fine for "normal" conditions and changes fast enough to compensate for depth, temperature, or pH changes, but sometimes you don't want to compensate at all. Turning up the sensitivity is the easiest way to find a thermocline I know. In Florida, a lot of sweet spots are around spring heads and sink holes which may or may not have a significant depth change. Turn up the gain and any thermolayer will reflect sonar clear as day. You normally will have to put up with some noise on the screen, but breaklines are easy to see even on a cluttered screen.

Manual Range - Another feature every unit has that is almost never touched. I like to use this one for chasing schooling fish over deep water. If the fish are in the first 10 feet, I really don't care what's on the bottom 40 feet down. I've still got the digital readout to see significant depth changes, but the reduced range lets me look in the area of interest, the upper 10 feet. About the only other time I go to Manual range is when I've turned up the gain and a thermocline or something is giving me a false bottom.

Fish ID - Shows you a picture of a fish if the echo return is arched indicating a suspended point body. This is the mostly used and misleading feature on modern depth finders. The theory is when in doubt show a fish, so you get a lot of false indicators. As mentioned in the section on displays, Hummingbird has taken this a step further in their multi-beam units by having different displays for fish on each side of the boat. Lowrance has the Fish ID feature I really like, you can turn it off without disabling the signal processing.

Fish Track - This one started showing up about 3 years ago and has caught on pretty well. When the Fish ID shows you a fish, this feature will show the depth at which it's suspended. Hummingbird will even draw you line to show you which fish it's talking about.

Menu Interfaces - I work with computers every day so I'm pretty sick of anything having to do with "Windows", but that seems to be the wave of the future in depth finders. Instead of having different buttons for different features, you press a "Menu" button for a series of feature control options. You repeatedly press the Menu button until the find the one you really want. I guess it's nice at night since you only have one button to find. Personally, I think it's just a case of trying to save a few bucks on buttons for the manufacturers. Either way, I guess we need to get use to it. Both manufacturers will allow you to customize the displays and windows, allowing you to define the features you most often use to come up first. One thing new for this year I do like, they don't take up the entire display with the menus. You can still see the graph in part of the screen even with the windows active. It would infuriate me to miss something good down there just because I was fooling around with the settings at the time.

Split Screen Zoom - This feature kicks in at the mid priced units, where the low end units just have full screen zoom. All units actually have more information in them than they can reasonably show in the limited displays. The Split Screen Zoom shows an up close and personal view of a part of the water column on one side, and a normal full return on the other. Oddly enough, I love this feature and use it often. Where I like it the best is when you are looking for short grass cover in deep water. The zoom lets you see even 2" or 3" grass in deep water where on a normal display is just appears as bottom clutter. With the split screen, you won't miss suspended fish or shad balls when you're looking.

Bottom Hardness - Lowrance has had their Grayline feature for a number of years and this year Hummingbird answers back with Graphlook, which does the same thing. Instead of limiting the return to the bottom point, you get the sub-bottom return echoes as well. If you have a lot of muck on the bottom, it will absorb most of the signal so you get just a thin line showing the bottom, and even that may be broken up an occasionally disappear. Over a hard bottom, you get lots of returns and they show up as wide thick black line on the bottom. If you're over a firm silt bottom, you various depths of gray below the black line of the bottom. With a little practice you can find shell beds, silted over rocks, or silted in creek channels, all of which hold fish at times. Once you get use to it, you'll wonder how you lived without it.

Bottom Alarms - These where undoubtedly added originally for saltwater boats to avoid reefs, but with a little imagination, come in handy for bass fishermen as well. The units offer both an alarm for getting too shallow, but also have a "channel alarm" for getting too deep. If you're running a ledge with you trolling motor that rises, say from 20' to 15', put the lower limit at 19' and the upper limit at 17'. Now you can keep the boat in the right depth without ever looking at the screen! Another use is if you're working a deep water area, say in 18', set the upper alarm at 14'. If you happen over a brush pile or small hump while you're fishing, the alarm will make sure you don't miss it even if you happen to have a fish on at the time. I've found several pieces of cover I would have otherwise missed this way, and most of the time, the fish are stacked on any isolated cover.

Other Features in Common - There are several other features you expect that either overlap other functions or add to normal operation. Backlighting for night fishing is a must. Bottom Lock which keeps the zoom range measured up from the bottom instead of down from the top, (always shows the bottom and say 10 feet above it). Transducer Sensing, which automatically tells the unit which of the optional transducers is installed without you having to program it. Disable the Signal Processing gives you a pure return instead of going through the normal filtering and noise rejection. A common option is a 3D version of their upper line which adds a chart width dimension instead of just averaging the entire bottom. Another common option is a boat speed and/or water temperature probe with the information coming up on the chart. Chart speed adjustment allows you to increase the speed of the chart for added detail at higher speed. All of these things are the ones we've come to expect either from convenience or necessity.

Product Discriminators

A Product Discriminator is the latest buzz word for those features that set you apart for the competition. Each has a few, most of which aren't that important or else everyone would offer them. Or course the marketing types believe these features are the most important and any unit that doesn't have them is just junk. I guess that's why there is competition. For the most part, this is a pretty weenie list, but anyway, here are the ones that are brand unique.


Displays 1/10ths of Feet - This is the main reason I personally select Lowrance/Eagle units for my boat. In these shallow Florida lakes, it can take 1/4 mile to change depth by 1 foot. A lot of the structure I fish is only 3 - 6" deep on a flat. By reading out 1/10ths, I see these subtle changes that other brands miss. If I was in reservoirs or deep saltwater, it really wouldn't make a difference.

Disable Fish ID - Lowrance has this one right finally. In most previous units if you turned off the Fish ID display, it turned off the Advance Signal Processing as well, since that's where the feature was programmed. Now, you can disable the display and leave all of the filtering and noise reduction in place.

Power Down Memory - Lowrance products have a Static RAM chip on their processor to store the current settings and configuration. If you like to make manual adjustments, like turn off Fish ID or turn on Split Screen Zoom, then this means you won't have to do it every time you turn on the unit because it saved your set up from the last time. If you always run in automatic, chances are you don't really care about this feature.

Fast Track - For those of you who still prefer a flasher to a graph or LCD because it updates quicker, the Fast Track system gives you a vertical bar down one side of the display with the instantaneous updates of a flasher. This option can make sure you don't miss isolated shad schools or spot cover when running at high speed. Just make sure you look up occasionally to make sure my boat is setting in front of yours.

GPS Compatible - Actually, this is a bit of a misnomer since it's really the GPS product line which has an optional Sonar Module you can add. But either way, they are one of the few sources where you can get both GPS and Sonar in a single unit.

Tri-Temperature Capable - Here's one for a hot summer night. Every brand offers some type of option to give you boat speed and water temperature. Lowrance has taken in a step further and gives you Water Temperature, Air Temperature, and Livewell Temperature. For real heat sensitive people and fish I suppose.


Wide Screen Display - This is their major claim to fame and what they said "everyone" wanted. They add another 30% to the horizontal width so a plotted feature stays on the screen longer. It's suppose to let you see big complex structure in one piece even at slow speeds. It results in an effectively slower screen scroll without any loss of resolution.

Programmable Zoom Range - For suspended fish, this is kind of neat. Instead of zooming in on the bottom or limiting the range on the top, you can select the zoom depth to be anywhere in the water column. It also works with their split screen zoom. If you were in 40 feet of water and wanted to look at everything from 10 to 30 feet in a full vertical display, this would let you do it.

Side Fish Displays - We've mentioned this one before. With their 3 beam transducers, fish on the right side of the boat show up as hollow fish images facing right. Fish on the left face left. Fish pretty much under the boat a filled in as normal. Kind of a cute way to squeeze more information on the display without having to resort to 3D view.

Anti-Glare Lens - A new coating for all of the displays. In the past, the anti-glare coats have reduced viewing angles and made reading the display difficult with polarized sunglasses. The new lens is suppose to give better viewing under all light conditions.

Quick Disconnect - For those who like to make sure the unit is still on the boat the next trip, Hummingbird is still the only manufacturer to offer a quick disconnect mounting bracket. Their bracket design saves wear and tear not only on the connectors, but the cable runs themselves. Pretty slick.

Contour View - This enhances two dimensional bottom detail by separating cover from the bottom. ??? Monster Digits - If you only care how deep you are and not what's down there, it uses the entire display as a digital display. I guess this is meant for old farts like Biddle.

Well, that's it. You pays your money and takes your chances. Any of the modern units are a huge advance from what was offered only 4 or 5 years ago. We can expect better in the coming years, but this year looks pretty good!

Paul Crawford

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