Depth sounders are pretty crucial bits of kit for all of us. If you want to have an idea of how much water is beneath your keel then you will need a depth sounder of some sort - unless you want to go old school and send someone to the bow with a longline and weight...

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The trend in recent years is towards boats running the vast majority of boat data through a chartplotter or Multi Function Display (MFD) but most of the best depth sounder models still come with a separate specific LCD display screen. The display itself is reasonably simple and the key concern is ease of use as well as brightness of the display and backlight functions. However, to get a depth reading you will need to fit a transducer into your boat.

When fitting a stand-alone depth sounder it sometimes comes with an in-hull transducer. These are mounted in a plastic tube and is fitted vertically to the inside of the hull. The tube contains some oil beneath the transducer itself which allows good sound transmission through the hull. If you fit a dual speed/depth transducer, or another type of through hull transducer, it will need to be mounted through a 50mm diameter hole in the hull.

Depth transducers transmit sound pulses or ‘pings’ that bounce back on hitting the seabed. The time the ping takes to travel down and return is a measure of the distance to the seabed. The only difference between so-called ‘analogue’ and ‘digital’ transducers is that, in the latter, the signal is sent out as data over a NMEA interface.

Best depth sounders available right now

Raymarine i50 depth sounder

Best depth sounder for usability

The Raymarine i50 instruments are designed to complement Raymarine’s latest generation multifunction displays. The i50 comes in a number of different options. The i50 depth offers only a depth readout, while the i50 Tridata display offers speed and depth, while a measure log tracks distance sailed.

The screen features excellent viewing angles for both day and night conditions and simple, push-button controls make i50 instruments easy to see and use. This display is offers low power consumption, has a good red lighting for visibility in the dark and is easy to install. This has fast become one of the most popular depth sounder display units on the market.

In terms of the transducers on offer from Raymarine there are several to choose from. Raymarine does offer an in hull transducer (the P79) and a range of options for through hull depth alone the best of the bunch if you are looking for standalone depth would be the P19. These would be the transducers most likely to go with the i50 depth display as a standalone depth sounder.

To fully take advantage of the display, you would want to consider a depth and speed transducer sold alongside the display as a kit. The D800 is a Smart multisensor by Airmar – supplier of the majority of depth transducers on the market – that offers depth, speed, and temperature functions in one thru-hull fitting. Digital signal processing inside the housing provides depth, speed, and temperature data to a chartplotter, radar screen, or digital display such as the i50.

Buy Raymarine i50 Depth kit on Amazon (UK)

Buy Raymarine i50 depth kit on eBay

Buy Raymarine i50 Tridata kit on Amazon (UK)

Buy Raymarine i50 Tridata kit on eBay

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Nasa Marine Clipper

Best low cost depth sounder

Nasa has built a solid reputation for building marine electronics that work well, are affordable and simple to use. As such, NASA’s Clipper range is well known by now and trusted and is a particular favourite of small-to-medium-size boat owners. Whilst they might not be the flashiest instruments, they do a pretty good job and are available as stand-alone analogue devices for a very reasonable price.

The Clipper Depth looks somewhat dated, but the digits are very large and easy to read from a distance, which is more important than having a fancy trim. The supplied in hull depth transducer wires directly into the display head, offering a no-nonsense, easy to fit depth option without many bells and whistles.

Nasa Marine also provide a Clipper Duet option which comes with a through-hull transducer, enabling speed and depth measurements. Installation is slightly more complicated due to the through-hull transducer, but this is a very cheap way to get speed and depth onboard.

Buy Nasa Marine Clipper Depth from eBay

Buy Nasa Marine Clipper Duet from eBay

B&G Triton 2

Best top-end depth sounder

B&Gs Triton² provides sailors with a clear view of key instrument data such as speed, depth, wind and heading along with a dedicated SailSteer technology page. For the majority of these functions you will require further B&G kit, but given their position in the market as the go-to instrument supplier for serious racers it is hardly supposing they would expect users to be considering more than simply depth alone.

Combined with a Triton² Pilot Keypad, the display can also serve as a complete autopilot control system. The display is a low profile design, and offers an efficient LCD screen and easy installation makes it the perfect choice on cruising sailboats, or integrated within a full navigation system on cruising and racing boats.

You can buy Triton² display units with either a depth/speed though hull transducer or to take full advantage of the unit’s abilities with a depth/speed through-hull transducer and a wired wind pack all of which will allow the use of B&Gs SailSteer technology. The whole lot can also be purchased as a wireless package.

Buy B&G Triton² depth/speed package from B&G

Buy B&G Triton² depth/speed/wind package from eBay

Buy B&G Triton² depth/speed/wind wireless package from B&G

Garmin GNX 20

Best depth sounder for customisation

The easy-to-read GNX 20 marine instrument display from Garmin displays black digits on a white background, or background in a variety of colours. It is able to display depth, speed, wind and 50-plus marine and boat parameters. Its glass-bonded display with anti-glare lens coating provides good daytime and nighttime readability with high-contrast digits scalable up to 36 mm.

Fully customisable user profiles allow you to choose from five available display configurations for sailboat or powerboat user-profiles: single, dual and triple function, plus gauge and graph mode to display wind, depth and speed data, or customise the pages to display the marine and boat data that is most important to you.

It’s NMEA2000 compatible and, as with many of the depth sounders in this list, is designed to work alongside a main MFD unit. To make the most of the functionality of the GNX 20 you will want a full functioning through-hull transducer, such as the DST 800 by Airmar.

Buy Garmin GNX 20 unit on Amazon (UK)

Buy Garmin GNX 20 unit on eBay

Buy Airmar DST800 Transducer from eBay

Plastimo Echotest depth sounder

Best for depth measurement without installing electronics

This handheld device requires no installation at all to your boat and is very simple to operate. It is totally waterproof and gives readings to a maximum depth of 80 metres. The Echotest has a Large LCD Display with LED back light, making it useable at night.

To use you need to dip the head into the water to see how much water is beneath you. It runs off a 9V drycell battery. This is certainly not the most accurate or best option if you have a larger boat but for those planning on a bit of dinghy cruising, or without power onboard it could offer a decent option.

Buy Plastimo Echotest depth sounder from eBay

Best sonar systems on the market

If you want to go one step further in your understanding of what lies beneath, you may want to consider a forward-looking sonar unit. The latest models of marine sonars can be powerful tools for both cruising and racing yachts. Such has been the improvement that you can now get sufficient clarity to pick out areas of seagrass and patches of sand in an anchorage.

Broadly speaking, the improvement is thanks to the availability of CHIRP transducers that, unlike a traditional sonar, can distinguish between multiple targets through scanning using a signal of varying frequency. This enables them to show individual fish, rather than just indicate a shoal, to resolve vegetation growing on the seabed, and distinguish between a sandy/muddy shoreline and a rocky one.

B&G ForwardScan

B&G’s ForwardScan sonar has a 180kHz transducer, and can scan the seabed over a 15° arc up to 90m forward, but this can, and will, reduce depending on bottom conditions and water depth.

As well as showing a graph of the depth ahead of the boat, the ForwardScan data can also be superimposed on a chart, with shading to indicate safe, warning and critical depths, which makes it much more intuitive to use. ForwardScan uses a removable slimline transducer that extends 31mm below the hull.

The company offers a selection of models in the range, suitable for different purposes including a StructureScan transducer, which is geared towards fishing markets and to show more detail of the seabed.

Buy B&G ForwardScan transducer from eBay

Echopilot FLS 3D

Echopilot’s range is optimised to show as much detail of the seabed as possible, rather than focussing primarily on displaying fish. It updates quickly and so, the manufacturer claims, can be used at speeds of up to 20 knots. This represents a significant boosts to old systems, which were only really usable at very low speeds or sub-5 knots.

A more powerful FLS 3D model has twin retractable 200kHz transducers that give a 60° beam width. The range extends to 20 times depth, so around 200m in 10m of water. Echopilot claims it can detect rocks at up to a distance of 500m. This more powerful offering does offer much more in terms of data readability. It does offer a three-dimensional picture of the ground ahead, and better accuracy from distance, but the price is greatly increased.

Buy Echopilot FLS 3D with Dual Pro Transducers on eBay

Garmin Panoptix

Many fishfinders, including many of Garmin’s own, show only the area below the boat or at the sides, but Garmin’s Panoptix products offers through-hull transducers intended for fitting to yachts and has forward-looking functionality.

The FrontVü mode displays the seabed ahead of the boat in impressive detail but as with the similarly detailed B&G offering, only at a range of up to 90m, reducing to eight to ten times the depth of water in very shallow water. The scanner has a 20° beam width and provides a clear picture at boat speeds of up to 8 knots.

The LiveVü Forward function allows you to see fish and the structure of the seabed at a reduced range of up to 30m. Both options are offered with the PS51-TH transducer at a cost of £1,360. This unit is a similar size to that of the B&G ForwardScan transducer.

Buy Garmin PS51-TH transducer from eBay