Difference Between a Chartplotter and Fish Finder? A Complete Overview

Technology has come a long way in helping anglers navigate waterways and locate fish on the bottom. The days of using a physical map and compass are all but gone. We can now plugin coordinates and allow a machine to precisely navigate us to our destination. One thing you must be aware of is the difference between a chartplotter and fish finder.

A fish finder unit uses SONAR technology to scan and give you a picture of the bottom. It does not provide navigation assistance, whereas a chartplotter uses GPS to help you navigate waterways safely. Each unit can be purchased separately or, more commonly, together as a combined unit. 

Understanding what to look for when purchasing a unit allows you to tailor its use to your style of fishing. Below we will review the newest technology and what to consider when making a purchase. Lastly, we will review one of the best combo units on the market today for under $1200.

fishfinder screen

Do most fish finders have GPS?

If you are interested in both charting and sonar applications, there is no need to purchase two separate units. 

The majority of marine units combine GPS functionality with fish finder units to create a single unit offering. Stand-alone fish finders can still be purchased and are much cheaper than a combo unit; however, these are becoming less popular.

If you are an avid fisherman, I recommend having a combined unit on your vessel. The combined unit is most beneficial when fishing offshore in the ocean or if you frequently travel to unfamiliar fishing destinations. 

gps unit screen

How does a fish finder work?

Fish finders are essentially an underwater camera that shoots continuous pictures. Rather than using light like a traditional camera, a fish finder uses sound to capture images. This sound technology is referred to as Sound Navigation and Ranging or SONAR. 

Fish finder units are with a transducer. The transducer is attached under the vessel’s waterline and is linked to the display of the unit. The transducer is responsible for sending out sound in a downward motion towards the bottom. As the sound bounces back to the transducer, it deciphers the distance of objects based on how quickly the sound returns. Sound travels extremely fast through the water at a rate of one mile per second. Doing so allows the transducer to send multiple sound pulses per second to create a continuous display of the bottom. 

Do fish finders show depth?

Sonar reflections allow the fish finder to determine the bottom’s depth and pick up any objects that sit higher than the bottom, such as large rocks, shipwrecks, and even fish swimming in the water column. 

This is extremely useful when looking for reefs or live bottoms that hold various fish species. The density of the structure is outlined in varying colors that allow you to decipher between what may be coral versus foliage, such as seagrass. Fish will generally appear as a streak or an arch higher in the water column.

 Identifying fish will take some time to master, as any interference in the sound frequency will send a mark back to the head unit. Often what may appear as fish can be a bait pod, a clump of grass, or interference from a running motor. 

In addition to scanning the bottom, fish finders utilize a sensor that will tell you water temperature at the surface. This is extremely helpful when targeting species that prefer water temp breaks or prefer a specific temperature. 

Traditional sonar vs Side and Down imaging

There are a few limitations to traditional sonar. The main limitation is the field of view. The sound transmitted by the transducer is sent to the bottom in a cone-shaped manner. As the sound leaves the transducer, it will spread until it reaches the bottom. This essentially creates a two-dimensional view of what is beneath you. Unless you are directly above the structure or fish, the unit is unable to capture the image. 

Technology manufacturers have refined SONAR capabilities by introducing Side and Down imaging. These features allow for a crisper, more three-dimensional view of the bottom and expand the field of view. 

down imaging example

What is Down imaging?

Similar to traditional sonar, Down imaging captures what is beneath the vessel. Whereas traditional sonar uses a cone-shaped sound frequency, down imagining uses a thinner and wider trajectory. The altered trajectory allows down imaging to return a clearer, more detailed picture of what is below. 

Although traditional sonar may be capturing the same area, the cone-shaped view distorts the interpretation of the image. Down imaging on the other hand orients the image in a way that appears more natural to the eye as if you were looking under the water. 

Both technologies will help you locate structure and fish, but the detail of down imaging will show a more picture-like image of things such as a sunken ship or tree under the water. 

Almost all manufacturers offer down imaging. The names used for the feature will vary from company to company. For example, Humminbird refers to the feature as Down imaging whereas Lowrance calls the feature DownScan. 

side imaging for chartplotter vs fish finder

What is Side imaging?

Side imaging is similar to Down imaging because it gives you a clearer picture of structure below the water. The key difference between the two is that side imaging allows you to see what is below and to the boat’s sides. Rather than shooting a thin sonar beam downward, Side view sends the beam out to the sides. 

This allows you to see detailed structure hundreds of feet to the side of your vessel. As you can imagine this is great for scanning further distances or allowing you to find the structure that may not be exactly on the GPS mark. 

The unit’s display will show data to the left and right of the boat using gridlines to show the distance away from the vessel. The scanning distance can be adjusted to show a narrower view with more detail or expanded wide to pick up structures.

Side imaging is an incredible tool for seeing fish. Schools of fish or large species can be picked up with such detail that you are able to decipher the species of fish shown. I have found Side view very useful when scanning dock lines or rocky banks. 

What to look for in a fish finder

Understanding how you will use your fish finder is the most important factor when selecting one to purchase. Technology advances have paved the way for some incredible sonar views and the ability to zoom into detail. Some units even have the ability to interact with other components on your boat such as the engine, trolling motor, and radar. 

Although this technology is great, it can become quite overwhelming. Let’s face it, if you don’t understand how to use the feature, then it doesn’t provide any value. Not only will an abundance of features make it difficult for you to navigate the unit, but the costs can also be astronomical!

Over my years of guiding, I have used many different fish finders and the features they offer. I have created a list of considerations I use when selecting a fish finder from my trials and errors. 

Get the larger screen! 

No matter how big the display is, it will never feel big enough. I would never use a unit that has a display smaller than 7” for inshore fishing and a minimum of 9” when fishing offshore.

Avoid touch screen only models. Having a touch screen is a nice feature, but it can make navigating the screen difficult when your hands are wet or dirty. If you enjoy touch screens, I recommend a model with a touch screen and manual buttons.

Down View and Side imaging are a must

Countless times I have located new areas to fish using these areas. The added detail will allow you to better identify what you are looking at and help you see if fish are present.

Resolution is key

Screen detail is incredibly important when looking at a scan of the bottom. I would happily give up some bells and whistles for a display that has a sharper image. 

Ease of use

Each manufacturer will have proprietary technology such as 3-D views, map overlays, and scroll back features. Being comfortable with basic navigation such as marking waypoints and navigating split screens is far more important than these fancy features. If you are comfortable with basic navigation, you are more likely to learn the unit’s advanced features. 

screenshot chartplotter vs fish finder

Mapping considerations when selecting a chartplotter

All chartplotters will function in a similar capacity. Your location can be detected through a satellite connection, even when venturing off the grid. 

Chartplotters are designed to help you navigate in unfamiliar areas or when land is not visible. If you have ever fished deep in the ocean, then you are familiar with how quickly you can lose your sense of direction.

The biggest consideration when selecting a GPS unit is the quality of the maps. Each manufacturer will have proprietary base maps that show varying levels of detail.

For example, some maps may show you channel markers to help you navigate to deeper water. Other maps may be very basic only showing you what areas are land versus water. In either case, base maps are not the best selection for your chartplotter. 

Third-party mapping

A better option for running your GPS chartplotter is to use third-party mapping. Micro SD cards can be purchased that allow you to upload detailed mapping.

Third-party companies such as NavionicsFlorida Marine Tracks, and C-Map offer highly detailed maps that include things such as satellite imagery overlay and detailed markings of navigational hazards. These maps have regular updates that can be downloaded to display the most up-to-date maps.

The downside to third-party mapping is comparability with the units. Each mapping chip will be compatible with certain GPS manufacturers.

If having a detailed map is important to you, then selecting your third party mapping chip prior to purchasing a unit is advised. 

detailed map chartplotter vs fish finder

For offshore fishing, I highly recommend using a C-map chip to not only navigate offshore but the ability to see the bottom contour in a map view.

The best map for inshore fishing is without a doubt Florida Marine Tracks. No other map on the market has the same level of detail and accuracy.

Does a chartplotter require a transducer?

If you primarily fish shallow water such as flats, then a fish finder does little good in helping you locate fish. 

Flats guides and fly fishermen tend to be more concerned with the ability to get to areas versus what structure lies beneath.

In this situation it may be best to use only the chartplotter feature.

Using a chartplotter does not require a transducer to be installed. The transducer is used for sending SONAR signals to display the bottom. A chartplotter/fish finder combo can operate solely as a GPS unit by not installing the transducer.

Combo units can be purchased at a discount without the inclusion of a transducer. This gives added flexibility as you are able to later add a transducer to have both GPS and fish finder capabilities if you decide you need it.

One advantage of skipping the transducer is avoiding drilling holes in the boat’s transom for installing the transducer.

If you are frequently fishing shallow or poling over very skinny water, the transducer can become damaged by dragging against the bottom. This is another reason to avoid the use of a transducer if you are fishing shallow.

Best fish finder/chartplotter combo under $800

There is no need to break the bank to get a quality fish finder combo. A unit that has all the newest features can be purchased for under $800.

The best fish finder/chartplotter combo under $800 is the Humminbird 410950-1NAV HELIX 7 CHIRP MSI (MEGA Side Imaging) GPS G3 NAV Fish Finder

This Humminbird HELIX 7 model offers down imaging along with one of the best side imaging sonars in the industry. For inshore applications, the 7-Inch screen with 800H x 480V resolution color TFT display is roomy and provides a clear view.

Some other notable features include Dual Spectrum CHIRP Sonar, AutoChart Live, GPS, and built-in Humminbird basemap. In addition to the standard base map, the unit comes preloaded with a Navionics + map card. 

This unit packs a punch at a reasonable price tag. No other unit in this price range offers as many features. If you are thinking of purchasing a combo unit, I highly recommend you check out the Humminbird Helix 7.


Selecting a fish finder unit for your vessel shouldn’t be a daunting task. There are plenty of good units on the market at reasonable costs. I highly recommend the Humminbird 410950-1NAV HELIX 7 CHIRP MSI (MEGA Side Imaging) GPS G3 NAV Fish Finder to cover all your needs.

When selecting a fish finder unit, it is advised to buy a combo unit that includes GPS capabilities. For a small increase in price, you can have peace of mind in knowing you have a built-in navigational tool. If the use of mapping is a main selling point for you, make sure the unit is compatible with quality third-party mapping chips. 

A fish finder is only as useful as your ability to use it. All of the fancy features the manufacturers offer are nice, but ease of use should be a main consideration when selecting your unit. 

Where possible, it is advised to elect for the biggest screen that is affordable and features such as Down Imaging and Side Imaging are extremely beneficial. 

Sonar technology has come a long way over the years. If you are not using a unit with this new technology, then you are giving up a huge advantage when it comes to catching fish.