Sonar
How do you set up side imaging on a fish finder?
Quick answer
Side imaging looks sideways instead of straight down, so a boat in ten feet of water is not limited to the tiny circle a traditional cone covers there. A 20 degree cone covers only about 3.5 feet across at 10 feet of depth, while side imaging reaches far past it once boat speed, range and mount are set correctly.
Side imaging is the single feature that changes what a small boat can find in skinny water. A traditional sonar cone points straight down, so its coverage collapses to almost nothing the shallower you fish. Side imaging turns the beam sideways instead, reading a slice of bottom well off to each side of the hull rather than only the patch directly underneath it.
That difference is not cosmetic. In ten feet of water a 20 degree traditional cone covers a circle roughly 3.5 feet across, published trigonometry that every fish finder maker relies on and nobody argues with. Side imaging in the same ten feet of water is still looking 50, 75, even 125 feet to each side depending on the transducer, which is why it earns its keep in exactly the water where a down-looking cone earns almost nothing.
Getting a usable picture out of it takes three settings working together: boat speed, range and mount, plus one skill nobody teaches up front, which is reading the shadow an object throws rather than the return itself. All four are covered below, along with the published trigonometry behind the coverage numbers and where the manufacturer, not this site, is the authority on your own transducer.
On this page
How much water does a traditional cone actually cover?
This is the trigonometry every side imaging discussion should start from: coverage diameter equals twice the depth times the tangent of half the cone angle. It is published geometry, not an opinion, and it is why a boat idling over 10 feet of water with only a traditional cone is looking at almost nothing.
A 20 degree traditional cone covers about 3.5 feet of bottom at 10 feet of depth, which is the published trigonometry side imaging exists to work around.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Depth | Cone diameter covered straight down |
|---|---|
| 5 ft | 1.8 ft |
| 10 ft | 3.5 ft |
| 20 ft | 7.1 ft |
| 30 ft | 10.6 ft |
| 50 ft | 17.6 ft |
Coverage diameter equals 2 x depth x tan(angle divided by 2). A wider beam, 60 degrees at 83 kHz, covers more water but reads less detail; the 20 degree figure above is the default beam on most units.
What boat speed should you run for side imaging?
Every side imaging maker publishes a recommended speed range in its own manual, and it is worth reading rather than guessing. Run too fast and each patch of bottom gets too few pings to build a clean picture, so returns smear into a blur instead of resolving into a brush pile or a dock piling. Run too slow and you cover less water per trip than the unit is capable of showing you.
The honest answer is your own transducer's manual, not a number repeated across forums. A transom mounted unit and a trolling motor mounted unit often carry different recommended ranges because the water in front of each is disturbed differently, and the manufacturer measured that difference, not this site.
How do you set up side imaging step by step?
- Mount the transducer level and unobstructed. A transducer that is tilted, mounted behind a strake, or sitting in disturbed prop wash reads noise instead of bottom. A transom transducer built for MEGA Side Imaging needs a flat, unobstructed run of hull ahead of it, and a kayak scupper mount needs the scupper itself to sit in clean water at rest, not just underway.
- Pick the imaging frequency for the job. Traditional CHIRP and side imaging frequencies are not the same beam. Higher imaging frequencies, in the 455 to 800 kHz range depending on the maker, are what actually resolve individual pieces of structure rather than a general shape on the screen.
- Set the range to the water you are covering. Set the range to roughly what you want to cover on that pass, not to the unit's maximum. Over-ranging spreads the same number of pings across more water, which throws away the resolution side imaging is supposed to add over a traditional cone.
- Match your boat speed to the manual. Slow down until the picture stops smearing, using the speed range your own transducer's manual publishes as the starting point rather than a number you saw on a forum.
- Run structure in parallel passes. Run parallel lanes along a shoreline or a breakline rather than crossing it once. Side imaging shows a strip of bottom on each side of the boat, so overlapping lanes are what turn a strip into a map of the whole area.
- Read the shadow, not just the return. An object standing up off the bottom throws a shadow away from the boat on the image, and the length of that shadow says more about how tall the object is than the brightness of the return does. A short, wide return with a long shadow is standing taller than a bright return with none.
- Mark and log what works. Mark a waypoint on anything worth a second look and note the range and side it appeared on. A GPS linked chartplotter turns a good side imaging pass into a map you can return to on a different day.
How do you tell a stump from a rock pile on side imaging?
The return itself, the bright or dark mark on the bottom, tells you something is there. The shadow tells you what it actually looks like. A stump throws a narrow, sharp edged shadow. A brush pile throws a ragged one with soft edges. A rock pile sits low and throws almost no shadow at all because there is little height to cast one.
Distance from the boat matters too. The same object throws a longer shadow the farther it sits from the transducer, because the beam strikes it at a shallower angle out there. Two objects of identical height at different ranges will not look identical on the screen, and reading side imaging well means learning that relationship rather than treating every shadow the same.
Which side imaging units are worth setting up?
Humminbird Helix 7 CHIRP SI GPS G4
$579.99 Published specsSide Imaging on a seven inch screen at a price that makes it the default first side imaging unit.
Best for: A first side imaging purchase
Check price on Amazon
Lowrance Eagle 7 TripleShot HD
$599.99 Published specsSideScan, DownScan and CHIRP from one transducer, with C-MAP inland charts already loaded.
Best for: Fishing unfamiliar lakes where the chart matters as much as the image
Check price on Amazon
Garmin Striker Vivid 7sv
$519.99The Vivid color palettes make a shadow easier to separate from the bottom return at a glance.
Best for: Anglers already running Garmin who want SideVu on the same ecosystem
Check price on AmazonWhat do you mount the transducer to?
Berts Custom Tackle transducer mounting board, 12 inch
$23.99Slides fore and aft to find clean water without drilling the transom a second time.
Best for: An aluminium transom you do not want more holes in
Check price on Amazon
Lowrance kayak scupper mount for Skimmer transducers
$53.74Drops a Skimmer style transducer through an existing scupper hole with nothing drilled or glued.
Best for: A sit on top kayak with a scupper in a sensible spot
Check price on AmazonHow we chose
We did not test this equipment in person and we never claim to. Picks are researched from manufacturer specification sheets, published engineering and regulatory figures, and the recurring themes in verified owner reviews. Every pick is matched to a real thrust rating, a real published amp draw, a real capacity or a real conductor size rather than to a price bracket, and it is placed in the tier where its published capability actually belongs. We rejected the unbranded flood that dominates several of these search results, because a lithium pack whose management board is the only thing between a cell fault and a fire, a breaker protecting a battery cable, a life jacket and a bracket holding a two thousand dollar motor to the bow at highway speed are all parts whose failure has a consequence nobody can walk away from. Where a figure is convention rather than a published standard we label it that way, and where a manufacturer does not publish a figure we leave it out instead of estimating it.
Frequently asked questions
Does side imaging work in shallow water?
Side imaging works better in shallow water than a traditional cone does, not worse. A traditional 20 degree cone covers only about 3.5 feet across at 10 feet of depth, so it is nearly blind close to the surface. Side imaging reads sideways rather than straight down, so it keeps covering real water at depths where a traditional cone has almost nothing left to show you.
What speed should I run for side imaging?
There is no single correct speed. Every manufacturer publishes a recommended range for its own transducer, and running faster than that range causes each patch of bottom to get too few pings, so the image smears instead of resolving. Start at the low end of the published range and slow down further if the picture still looks blurry before assuming the unit is at fault.
Why does my side imaging picture look blurry or streaky?
Streaking is almost always speed, mounting, or range. Boat speed above what the transducer's manual recommends is the most common cause. A transducer mounted in disturbed water, behind a strake or in prop wash, is the second. Setting the range far beyond the water you are actually covering spreads the same pings thinner and is the third.
How do I tell if something is a fish or structure on side imaging?
Fish typically appear as small, isolated marks that move or disappear between passes and cast no shadow, because they are suspended rather than sitting on the bottom. Structure sits fixed on the bottom return and, if it stands up off the bottom at all, throws a shadow away from the boat. The shadow is the more reliable clue of the two.
Do I need a separate transducer for side imaging?
Some head units, like the Humminbird Helix 7 CHIRP SI, ship with a side imaging transducer already in the box. Others require buying one separately to match the head unit's imaging format. Check the specific model's own listing before assuming side imaging is included, because two units in the same product line can differ on this point.
What range should I set my side imaging to?
Set the range to roughly the width of water you actually want to cover on that pass, not to the transducer's maximum published range. Over-ranging spreads the same number of pings across more water, which lowers the resolution of everything in the image rather than showing you more detail farther out.
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Researched, not professional advice. This page is compiled from published engineering and regulatory figures, manufacturer specifications and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are boating convention rather than published standards, and they are labelled that way wherever they appear. Marine electrical work is not house wiring. Use tinned, finely stranded marine cable, size it for voltage drop and for the ABYC E-11 ampacity table rather than one or the other, and put overcurrent protection within seven inches of the battery positive terminal, because everything between the post and the fuse is unprotected. A lithium battery needs a charger with a lithium profile. Never load a boat past its capacity plate, and remember that canoes and kayaks carry no federal capacity plate at all, so their stated capacity is the manufacturer own figure. Wear the life jacket, and treat early season water as the hazard it is: cold water immersion takes your breath and then your hands long before it takes your core.