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Ethernet vs NMEA Networking:  What do they do?
by: Captain Lance Valentine

One of the great features of today’s modern fishing electronics is the ability to bring in data from outside sources (antennas, electric motors, temp probes etc.) and the ability to share any data from one unit on any or all of the other units in a boat.  Lowrance uses two unique systems to share data between units.

First, is the Ethernet system.  This is a simple system, requiring a single cord between units to allow data sharing.  With the newest Gen2, Gen3 or Carbon units the following data can be shared between units using an Ethernet cable: (Ethernet is NOT available on Elite, Elite Ti, Hook or Hook2 units).

  1. Sonar data: the sonar “source” can be selected at each unit and ANY transducer that is connected to any unit can be viewed at any location.  For example, when trolling with a bow mount electric equipped with a transducer, you could view that transducer on a unit mounted on the console so you are seeing what is happening at the front of the boat, not behind you.
  2. StructureScan data: If your system is equipped with an LSS transducer (Side and Down scan), the input can be viewed on any unit that is connected via Ethernet cable to the unit receiving the input from the LSS transducer.  On older “button” units, a LSS box was used to plug the StructureScan transducer into. The box had 3 Ethernet outputs allowing up to 3 units to be sharing Ethernet data.
  3. Waypoints: All HDS units connected by an Ethernet cable are able to share waypoints.  By saving a waypoint on any unit, the waypoint will also be saved on all other units connected via Ethernet cable
  4. Map Chip data: on the newer Gen3 and Carbon units, one map chip can be viewed on all units connected to the unit where the map chip is inserted.
  5. Weather/Radio/Radar: the Sirius Weather and/or radio services can be shared to multiple units as can the 3G and 4G Lowrance or Simrad radar systems.

One of the questions we get a lot is “how many units can I hook up on an Ethernet system?”  The answer is simple…unlimited units.  You can “daisy chain” as many units and inputs together as you need, but there is a catch.  The Gen2 5 and 7” units have only 1 Ethernet port, allowing a unit to only share with a single other unit.  The Gen2 8, 9, 10 and 12” units, each have 2 Ethernet ports, allowing 2 additional units to be hooked (for a total of 3 in the system).  All Gen3 and Carbon units, regardless of screen size have 2 Ethernet ports.  If you need more capability, especially if using the Sirius or Radar products, you can install a NEP-2 expansion port.  This box allows up to 4 inputs/outputs and increases the number of products/units used on an Ethernet system.  In extreme cases, multiple NEP boxes can be hooked together to provide unlimited inputs and outputs.

Lowrance Ethernet Cable

Available in 6’, 15’, 25’ and 50’

Lowrance NEP-2 Expansion Port

Lowrance Ethernet Ports are easily identifiable by the yellow color

The second system is the NMEA 2000 or “LowranceNET”.  Often simply referred to as a “Network” this system allows users to bring in data from outside inputs such as GPS antennas, temperature probes, engine data, fuel level and flow, MotorGuide Xi5 electric motors and others.  In addition, a network can also be used to share waypoints between units of all vintages including the newest Gen2 and Gen3 units.

Hooking up a Network is a little more complicated than an Ethernet system.  A Network consists of a power node, a “backbone” (multiple ones may be needed), T connectors to connect each input device and unit to the network and a set of terminators at each end of the network.  Think of a network like the water system in a neighborhood…the backbone is the water main and each home is connected by a “T” connector to a pipe bringing water to the home.

Unlike the Ethernet system, a network must be hooked to a power source.  A Power Node is used to connect to a power source (be sure to have a way to turn the network off---it still runs after units are turned off) and uses a “T” connector to connect to the backbone.  Additional inputs and units can be added at either end on the backbone by simply installing a “T” connector to the backbone (or the last “T” connector in the line) then adding an extension cable between the device and the “T” connector.  The example above doesn’t show the option of using longer cables between “T” connectors. For example, on my boat I have the power node and 5 “T” connectors below the dash, a 15’ backbone cable up to the bow where there are 4 more “T” connectors and another 15’ backbone cable from the dash to the stern where there are 4 more “T” connectors. Below are pictures of the pieces needed to create a network.  The easiest way to install a network in your boat is to buy a “starter kit” which includes everything you need to hook up 2 units or 1 unit and one input device.  To add on to the system simply add a “T” connector and cable for each new unit or device you wish to hook up.

“T” Connector
Backbone and Extension Cables

Available in 2’, 6’, 15; and 25’ lengths

NMEA Power Node with “T”

120 Ohm Terminator Set---1 for each end of the network.

Using both systems is usually what ends up happening in today’s modern fishing boats.  In my current boat I have the following setup:

Hardware:  5 HDS units (2 on bow/2 on dash/1 in-dash for engine info and fuel
1 StructureScan 3D box
1 NEP expansion box
Ethernet Inputs: Sirius Weather/ ALL units are hooked to Ethernet cables via the NEP boxes to share waypoints, sonar inputs, side scan, down scan and map chips
Network Inputs: Point 1 GPS antenna/MotorGuide Xi5 bow mount electric motor/Link-8 Marine Radio with distress call/Engine data/ Engine water pressure/external water temperature/Fuel level/Fuel flow/Oil level/
ALL units are hooked to the Network via “T” connectors.

Here is a look at a friends’ boat (his is a LOT neater than mine!)…notice the multiple NEP boxes, yellow Ethernet cables, red network cables and “T” connectors. The big box on the left is a SonicHub music system and the small box on the right is the Sirius Weather module…

Most anglers will never have this much equipment on their boats but the basics of the systems remains the same.

If you have any questions about Ethernet, NMEA networks or any other install questions, please feel free to contact us at  Please put “boat rigging information needed” in the subject line so we can get your email to our experts.






Fish Arches • Where do they come from?

by Captain Lance Valentine
In the 2 decades I have been teaching sonar use and interpretation, the misunderstanding of fish “arches” is still the biggest issue most sonar users have, and it is probably the biggest reason that most anglers do not trust or fully understand what they are seeing on their screens.  We’ve all seen the beautiful ads-a sonar screen full of fish arches.  Although you may often see perfect, full arches on your sonar, don’t despair if you can’t.  The geometry of making a fish arch is simple, but must be completely satisfied before a fish arch will appear on your display.

Let’s go back a few years to high school geometry class.  Remember Pythagoras’ theorem?  The one that says that in a right triangle the hypotenuse will be longer than its opposite leg?  Don’t remember?  Maybe this will help you understand.

The distance from the tip of the triangle (transducer) to the outside point (A) is longer than the distance from the transducer to the bottom of the cone on a straight line (B).  What does this have to do with sonar and fish arches?  Believe it or not it has everything to do with fish arches.

Before we can get to how fish arches are actually made, realize that for a fish arch to form movement must occur relative to the fish and the cone angle.  For a perfect fish arch to occur, the fish must move completely through the entire diameter of the cone.  A fish that swims into the cone and remains there will show up as a solid line at the same depth.  Only as the fish is exiting the cone will an arch form.  A fish that only swims through only part of the cone will also not show up as a fish arch.  A fish must move completely through the entire diameter of the cone for an arch to be formed!


Now let’s imagine a fish setting still in the lake.  Our boat approaches the suspended walleye.  As the fish first hits the edge of the transducer’s cone, the display shows this contact (A in the illustration).  At this point the fish is the farthest it can be from the center of the cone and still be inside the cone.  As the boat continues forward, the fish gets closer and closer to the center of the cone, until at a single instant the fish is directly in the center of the cone (B in the illustration).  Now the boat continues further forward, causing the fish to get further and further from the center of the cone until the point where the fish is no longer in the cone at all (C in the illustration).

Notice how geometry affects the picture on our sonar display.  As the fish enters the cone, swims to the direct center, then goes out the other side, the distance the fish is from the center of the transducer creates a perfect arch.  Even though the fish’s depth never changes, the distance from the transducer does-further away at the cone’s edges and closest in the direct center.

With this is mind it’s important to remember a few key points.  The true depth of a fish shown on the sonar is the shallowest part of the arch plus about 1 foot!  Remember our transducer is about 1 foot under water making the distance to the transducer less than the distance from the fish to the waterline.  Also note that the length of the arch only tells us how long the fish stayed in the cone and has no correlation to the size of the fish.


So how do we tell how big a fish is?  The larger a target is the stronger the return will be, which the unit displays as a thick mark.  The larger a fish is the thicker the mark will be.  Determine a fishes’ size by the number of vertical pixels a target turns on.  A short, thick mark is a bigger fish than a long, thin mark!  Today’s color units also make it easy to identify a large versus a smaller fish.  By using different colors for varying intensity of returns, big fish will be seen as a different color than smaller targets.  I like to use Palette 1 on my Lowrance units, which shows bigger fish as yellow.


Now the most important part about fish arches.  If a fish does not move completely across the entire diameter of the transducer cone there will be NO fish arch.  That’s right no fish arch.  But you will see what is probably the most common way of seeing fish on a sonar display-a half arch (see picture below).
This is exactly what it sounds like-half of a full fish arch.  These half arches occur when a fish skirts the edge of the cone or moves through only part of the transducer cone.
Now that you understand the geometry of a fish arch, imagine a boat traveling 30 mph across the lake and a walleye slowly cruising at 15 feet deep.  How probable is it that these two moving objects-the 5-foot diameter transducer cone and the walleye-will pass perfectly enough to create a fish arch?

Hopefully the above picture looks familiar.  Now you know how fish arches are made-and why they sometimes don’t show up even when there are fish in the cone.  Start looking for half arches, learn how to tell the difference between game and bait fish and you will be surprised at what you start to see.

Keep an eye open for many more detailed articles on how sonar/GPS and other functions work by visiting  If you need to learn how to best interpret your sonar unit, be sure to check out our popular DVD “Sonar Interpretation”.  This DVD covers all aspects of sonar setup, features, interpretation and tips and tricks for traditional 2D sonar and SideScan and DownScan sonar regardless of what brand you are using.  You can order the DVD or download the seminar at