Article by Capt. Steve Katz
Our favorite fishfinders, sonar, bottom machines, depth finders, sounders… whatever we call them, all operate using a transducer. The transducer is in contact with the sea water below the boat and plays a major role in the quality of picture received on the sounder display. Transducers come in many different sizes, types and mounting styles. Picking the correct unit for your boat and sounder display can be difficult, costly and confusing. This article will help you understand the basics of the types, sizes and mounting styles of transducers and make your next purchase a little easier.
Basic Operation and Types
Inside a transducer is a single ceramic element or multiple ceramic elements, called Piezoceramic elements. These elements are tuned to operate on a certain frequency, such as the traditional 50 kHz or 200 kHz. The low frequency of 50 kHz is used to read deep water, while the higher 200 kHz provides greater resolution in shallower water. Some transducers only operate at single frequency so if you wanted both 50 kHz and 200 kHz you would need to purchase and install two separate transducers.
Most transducers have both 50 kHz and 200 kHz elements contained in one housing, allowing a single transducer to operate at either or both frequencies at the same time if desired. CHIRP transducers operate over a range of frequencies “sweeping” across the ranges above.
The performance of transducers varies with the size and quantity of the ceramic elements inside the transducer. Higher wattage, high performance transducers have multiple elements inside the housing. The picture below shows the internals of an Airmar B260 with 7 elements for 50 kHz and one large broadband element for 200kHz.
Below is a picture of the three elements inside of the B164 tilted transducer, it is capable of handing 1000 watts of power at 50kHz or 200kHz.
Transducer Size
There are two related size measurements for transducers. One is physical dimensions and the other is power handling, rated in watts for traditional transducers. Generally, a higher wattage transducer is physically larger than a smaller one. The size of your boat and the available access in the mounting location are often the determining factor on what size transducer you can install. Cost is also a factor, with the largest transducers costing at least a few thousand dollars. The transducer also has to be compatible with the display hardware. Make sure you check with the manufacturer who often has a list of compatible transducers to choose from.
For example, the popular 600 watt, B744V thru-hull transducer is 5.5” long, while the 2,000 watt, R99 thru-hull transducer is 22” long. Another example is the tilted element style, 600 watt, B60 transducer that is 3 ½” in diameter while the 1,000 watt B164 transducer is over 5” in diameter.
The size of CHIRP transducers varies greatly based on performance and sensitivity.
Mounting styles
Popular mounting styles include thru-hull, in-hull, transom mount and other variations such as pocket mount and tilted element.
Thru-hull transducers require drilling a hole in the bottom of the boat to allow the external transducer body to connect to the inside of the boat. A pocket mount is similar, though the fiberglass on the bottom of the boat is modified by a professional to form a recessed pocket that allows the face of the transducer to be flush with the bottom of the hull, eliminating drag and turbulence which allows for better sounder performance. If a pocket is not used, a traditional thru-hull transducer is usually accompanied by a high speed fairing block. The plastic fairing block is shaped like an airplane wing designed to smooth out the water flow around the transducer, reducing drag and turbulence. This fairing block can be quite large and are usually suitable for larger boats, since the large size can detrimentally affect the handling of a smaller boat. Caution must be used when taking the boat out of the water to avoid damaging the exposed transducer.
The transom mount is the most popular transducer style, accommodating a wide range of boats sizes, types and materials. This mounting method does NOT require drilling a hole in the bottom of the boat. A mounting bracket is attached to the transom of the boat to allow the face of the transducer to be parallel with the bottom of the boat. The transducer wire usually runs up the transom and enters the boat above the waterline. This is the least expensive mounting style and popular with do-it-yourself boaters. Just because they are transom mounted does not mean quality needs to suffer. The popular B260 is available in a TM260 transom mount model and the TM265 CHIRP transom transducer is also a very good unit. While a TM260/TM265 is a large piece of hardware hanging on the transom, it may be a reasonable choice for boats with limited interior hull access.
The Tilted Element style transducer has become very popular the last few years. While this is a thru-hull, it does not require a fairing block. This transducer is installed flush against the bottom of the hull and is internally compensated to match the angle of the hull, allowing the sound waves to travel perpendicular to the surface of the water. This is a transducer that is great for boats that are trailered, sit on a boat lift or stored using a forklift service. Large boat owners also use this style due to the reduced drag and ease of installation.
The final, common type of installation is the in-hull tank mount. This is only suitable for boats with a solid fiberglass hull. The transducers sound waves can travel through a solid hull and into the water with only a slight loss of performance. This installation requires a liquid filled tank attached and sealed to the inside of the hull. The transducer is mounted inside this tank and then filled with fluid such as propylene glycol. Since this can be installed from inside the boat, it can be done while the boat is the water keeping the installation cost lower than the traditional thru-hull installation method.
Learning about the different types of transducers and installation methods allows you to make an educated decision on the best option for your boat and sounder hardware.
Captain Steve Katz is the owner of Steve's Marine Service and holds NMEA MEI, AMEI, NMEA2000 certificates, ABYC Master Technician certification and factory training from many manufacturers.
