Forward-looking sonars

Case History

By Dick Beaumont

Fifteen years ago, on passage from Kota Kinabalu, Malaysia to Phuket Thailand, in Moonshadow, my Tayana 58, I motored, at dusk, into an anchorage called Port Klang, in northern Malaysia, it was very aptly named as we later found out. The anchorage there was clearly marked on my Navionics chart, as you can see below (see Fig.1).

I selected my anchoring position in 6m over a flat mud seabed and then continued to box the anchor, scanning the bottom to ensure there were no bommies, rock outcrops or seaweed beds in the 40m swinging circumference (anchor chain length plus the boat length) surrounding my selected position.

All was good for 3/4 of the circle when suddenly crash, or perhaps klang, we hit something very hard and unforgiving. I backed up along my track and ran below to see if we were taking in water. To my relief it seemed that the 20mm thick hull of Moonshadow had withstood the collision and I found no water in the bilge, my pulse rate started to return to normal. I checked the chart again, we were clearly in the area marked as an anchorage and surrounded by dozens of small coasters and large fishing boats (see Fig.1). 

Two of my crew went up on the bow with big diving torches to scan the water where we had crashed. Nothing. With my confidence at a low ebb, I very slowly turned Moonshadow round and followed my track back 100mts or so, selected another area of flat mud, still at 6m, and again proceeded to very gingerly box the anchor, with my crew peering in the torchlight into the turbid waters. This time all was completely clear and I dropped my anchor in the circle of certainty I had created. When dawn came I donned my diving gear, took a torch, because the water visibility was less than a metre, and jumped in to inspect the damage. To my horror, I discovered a gouge in the hull three feet (1m) long. The gouge was the depth of my thumbnail. We could only have ⅛” (2-3mm) of GRP left between us and disaster. I used a two-part epoxy putty which sets underwater, which I always carry onboard, to temporarily fill the gouge, and got back on board ready to head on to Phuket. There was no chance to be hauled out until Phuket. Before leaving I was determined to find out what we’d hit, so took the dingy over to the collision area, and slipped over the side with my mask and snorkel. There, sitting with its bridge section just three feet below the surface, was the wreck of a small steel coaster. The paint was still on her, she had clearly been down only a few months or so.

I sailed on up to Phuket, hauled out at Boat Lagoon to repair the damage and had an Interphase forward-sonar fitted. The penny had dropped for me; just because there’s 6m beneath the boat does not mean there’s 6m depth in front of the boat. That piece of equipment improved my confidence no end when going in to anchor anywhere new and after dark. I’ve lost count of how many times I have arrived at an anchorage later than expected and been obliged to sail on through the night rather than risk going in after dark. The forward sonar changed that completely, allowing forward vision underwater as well as above the surface day or night.

Another significant benefit is being able to get in closer to land and sit in calm, sheltered water while other yachts further out spend the night rolling around in a swell for fear of going in to close and grounding.

The forward-sonar also allows you to get close in to a coral reef to drop scuba divers off, without the hassle of anchoring, launching the dingy and loading all the dive gear into it, or the fear of wrecking the yacht.  

In this manner, I spent three months sailing and diving uncharted coral atolls in Papua New Guinea, something you couldn’t consider without the forward sonar.

Forward-looking Sonars on Review

By Trystan Grace

To paraphrase Star Trek’s Captain Kirk, yachtsmen can now ‘boldly go where no man has gone before’ thanks to the forward-sonar. By installing a forward sonar it completes the advantages of GPS plotter systems loaded with electronic chart chips that can pinpoint your position above the water within a few inches and lets you see what’s below the water in front of your yacht as well.

Whilst GPS can tell you exactly where you are, it can’t however tell you what’s in front of you underwater. There are still plenty of remote uncharted parts of the world which reward the more adventurous sailors that get to them, with pristine untouched coral reefs and fascinating and sometimes primitive cultures, that remain largely unvisited by foreigners.  Poorly or uncharted seas represent a different challenge for the voyaging yacht as there is no certainty of the underwater terrain. A grounding or collision hundreds, or sometimes thousands, of miles from assistance could be catastrophic.

The earlier systems were expensive and required the insight of a Jedi Knight. Today as more of the mainstream electronic manufacturers are producing them the price has dropped considerably.

Many will think of fish finders when sonar is mentioned, but technology has moved on with CHIRP transducers that operate over a wide range of frequencies. The ability to scan past objects and differentiate between bottom structures and topography with high definition imagery has dramatically improved safety. 

There are a few things to consider when buying a sonar and transducer. Higher frequencies produce far more detail than lower frequency transducers but do so at the cost of range. Smaller, less complex transducers are cheaper, but larger higher power transducers can provide clearer images with extended ranges in 3D.

Many of the sonar units will require a certain brand of chart plotter, so if you are installing a new system or thinking of upgrading, this must be taken into consideration. 

We have reviewed the three main market leaders as a starter guide.

B&G ForwardScan


Designed to directly integrate with their own plotters, the B&G ForwardScan has a 31mm,180kHz transducer which scans the seabed at a 15° horizontal arc and up to 90m in front of the yacht. This range does decrease quite significantly as you move into shallower water, providing a range of about 4x the depth. It has difficulty at times registering the seabed in shallow muddy waters but as it is paired with the depth information already captured from the chart plotter’s depth transducer, false readings are not common.

If you use a Vulcan or Zeus³ chart plotter, it allows direct connection between the transducer and plotter. If you have an older model plotter or if your cable length is more than 12m, you will need to buy the Sonarhub processor unit to pair up with the transducer. 

The depth data is presented onto a 2D graph which shows the area ahead of the yacht and can also be superimposed onto the chart. The ability to split the screen and show this arc in front of the yacht on the chart is a useful feature, however, the visuals overall are a little basic when compared to other models on the market. The price reflects this.

Price & Conclusion

ForwardScan Transducer with Sleeve and Plug £731 / €720 / $699

Sonarhub £628 / €617 / $699

The slimline 31mm transducer is a low impact appendage for the hull and overall the ForwardScan is easy to use, and comparatively easy to install. The visuals are a little basic but plus features include the ability to display a cone in front of the yacht on the chart mode. The range, depth and arc area are smaller than other brands and the range certainly drops off significantly in shallower water. However, if you are running a B&G system or are set on upgrading to their system, it is a good buy.



This British-based company has been leading the market for a number of years and offers three models that focus on seabed scanning over fish finding: the FLS Platinum Edition, FLS 2D and FLS 3D. Each varies in complexity and price. 

FLS Platinum Engine This option comes with a 45mm transducer, black box and video interface which allows it to display on third party chart plotters via VGA or HDMI. With a 30° horizontal arc, a 90° arc forward and down, it scans at 100m depth and 200m range forward. The graphics shown are similar to the B&G ForwardScan, a 2D cross-section of the waters ahead, however different colours denote how solid the scanned surface is, hard materials like rock in red or soft materials like sand or mud in blue.

FLS 2D – The FLS 2D is very similar to the Platinum, featuring the same arc, ranges and graphics, but it comes with its own 7” LCD display and with a choice of transducers. The standard transducer is the same as the FLS Platinum however the slightly larger professional bronze through-hull transducer (60mm) provides more details. The user interface is a little clunky compared to other brands.

FLS 3D – The FLS 3D is the flagship model and is quite a step up from the other two. It uses two 75mm units, each with two 200kHz transducers which allows it to show a 60° horizontal ahead of the yacht. The range shows at about 20 times the water depth. 

Like the Platinum model, it also plugs into third party chart plotters through the video aux mode and again through VGA or HDMI ports. We tested this model on a Raymarine unit and were unable to achieve a full-screen image, however, we cannot confirm how it is displayed on plotters from other brands. It does feature an HD full graphical cone in front of the yacht which makes mapping the seabed very easy.

The package includes the two transducer units, a black box processor, transducer interface and a helm mounted keypad.

Price & Conclusion

FLS Platinum Engine £1,000 / €1125 / $1,362

FLS 2D £1,179 / €1,325 / $1,569

FLS 3D £9,550 / €11,235 / $13,000

These units are quite cost-effective, especially for the sailor who does not wish to upgrade his navigation system to a certain brand. Although still a 2D display, the data is displayed with more detail than the B&G ForwardScan. The user interface is not as user friendly as the other models on the list but these units certainly offer higher detail and more range than the ForwardScan.

The FLS 3D is certainly the best model on the list however it comes with a high price tag. This model is certainly not for everyone but it will appeal to the ocean sailor who is planning on serious remote ‘off the grid’ blue water exploration where safety is the highest priority. The display shows an accurate 3D profile of the seabed which is easy to understand and, due to its dual transducers, it has an excellent range and depth. As it is not specifically designed for a certain chart plotter, it may not display perfectly on some models like the Raymarine plotter we tried. You will also need space to install the keypad which might be a problem if your helm console is tight on space. 

With all that said, it is an excellent unit and certainly, the best on our shortlist if money and consol space is no issue.

Garmin Panoplix™ PS51-TH – WINNER


Like B&G, Garmin has also designed and produced sonar equipment for their range of plotters. Their sonar range has received excellent reviews which are due in part to Garmin acquiring Interphase™, the leader in Marine Phased Array Scanning Technology in 2012.

Many of the Panoplix options are designed for fish finding, however, the Panoplix™ PS51-TH is a 50.88 mm through-hull transducer that provides a horizontal arc of 20° and 90° arc downward. The sonar data is displayed on a 2D cross-section like other models however it is a lot clearer and with more detail. The information is also displayed near-instantly, much faster than the other models tested.

In FrontVü mode, the range is about 90m range in-front of the yacht or about 8-10 times the depth of the water as it gets shallower. It will show a clear picture with boat speeds up to about eight knots.

The LiveVü Forward mode displays at a higher detail and it should be noted that with its 417 kHz transducer, has a higher level of detail than the other brands however this does come at a cost of range, bringing it back to about 30m in this mode. 

There is an extensive list of Garmin chart potters that this transducer plugs directly into so no black box is required.

Price & Conclusion

Ps51-TH £1,359.99 / €1,530 / $1,499

Although not a 3D display, the Panoplix™ provides the highest detail of the units on test. Its ease of connectivity to many Garmin chart plotters is a huge bonus for those sailors who are using or upgrading to a Garmin system. In FrontVü mode, the range in shallow water is impressive and if the detail is more important than the range, LiveVü provides great versatility.


All the forward sonars we reviewed offer a considerable advantage to sailors heading into unfamiliar waters, however, the B&G system has a much reduced forward range than the other systems. It may seem fine that in 50m of water you can see 200m in front of the vessel but a forward sonar is most useful in shallow waters, and in just 4m of water you can only see 16m in front of the transducers so only 14m off the bow, a boat length which isn’t enough to stop in unless you’re going very slow. 

The Echopilot FLS 3D definitely provides the best visuals but at a price that is above most cruisers budget.

After taking into account price, usability and detail, we think the Panoplix™ offers the best overall package on the market. It’s ability to see forward 8 x the depth is a big bonus and it will certainly improve the level of safety for your yacht and your crew.

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