Forward Looking Sonar

by Adrian on August 18, 2012

Forward Looking Sonar (FLS) provides a visual representation of the sea and seabed forward of a boat. Unlike a standard depth gauge which sends ultrasonic pulses directly downwards, FLS’s have special electronics which interpret the echoes bounced back from a forward facing transducer.

Forward Looking Sonar

Adding an FLS to a new boat is a no brainer. Not only does it provide a backup depth gauge, but it allows you to ‘see ahead’ to spot underwater rocks, corals, harbour walls etc.

The transducer mounting is key to performance – it needs to be located in an area free from physical and turbulence inducing obstructions. We carefully planned and calculated where in the hull our transducer should be mounted to provide the necessary unobstructed view forwards and it works perfectly.

An extra consideration for us during installation was to ensure the protruding sensor would not come into contact with hard ground when drying out. We considered all types of welded on protective fins, but eventually found a position that was slightly sheltered above the horizontal grounding surface of our hull. We also had to opt for the slightly more expensive aluminium through hull fitting to avoid corrosion from dissimilar metals.

There are 2 or 3 yacht friendly manufacturers out there, namely Interphase, a US company that I believe has recently been acquired by Garmin, and EchoPilot a UK company. There are other commercial solutions, but they start at tens of thousands of pounds.

The options:

1) EchoPilot’s top of the range FLS 3D model produces the most impressive panoramic forward looking view, but it is the most expensive, most power hungry (at 2 Amps) and requires multiple transducers. It produces a video image output which needs to be displayed on a separate screen or chart plotter video-in.


FLS 3D Scan

2) The Interphase iScan180 model provides both horizontal and vertical scanning modes which is useful and includes a dedicated colour screen with an additional video input, but the non-removable transducers are large and would be vulnerable to damage when taking the ground as they would protrude too much for my hull.

Interphase iScan180

Interphase Scan Diagram

3) The Echopilot FLS2D is the most basic model of the three and provides a simple vertical look ahead line graph type scan for the 10° directly in front of the boat. The transducer is compact, removable and tough. The device has its own dedicated 7″ colour display, draws just 380mA in use and is the least expensive of the 3 options, at around £850.

FLS 2d Screen
fls2d forward view graphic

In use:

The distance the FLS can scan ahead is directly proportional to the depth of water. That is, in 3-4m you can see 20m ahead. In 20m water, you can see 100m ahead.

So far, we have found it mainly useful when scouting around anchorages whilst deciding where to sling the hook. Watching the view ahead whilst circling will show the extent of shoaling and highlight any underwater rocks which may be within our swinging circle.

With our 1m minimum draught, the shallowest we’ve anchored in so far is 1.5m (in the non-tidal Baltic). The FLS allowed us to edge further and further into the bay with confidence.

We had hoped it may be useful at sea to detect the legendary submerged container, but there is no alarm function or analysis engine to detect a blip at surface level.

In summary, the FLS provides previously unknown information about the seabed and potential obstructions and allows safer exploration of shallow anchorages and unknown waters.

{ 2 comments… read them below or add one }

NBs November 9, 2017 at 06:16

Hey, thans your presentation FLS. I read it in the spring when I was doing the FLS acquisition. I ended up with Echopilot Platinum and it works fine. Here is a link to Vimeo, a small video about how Echopilot looks.

Best regards


Bottino Gian Luigi November 20, 2016 at 09:53

Buongiorno è possibile avere maggiori informazioni sul sonar FLS 3 D in italiano
Oppure un riferimento in Italia


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