Technical article from Lowrance
To select the transducer that's best suited to your needs, you need to consider the transducer's operating frequency, cone angle and type of installation.
Most of the sonar units that we sell accessories for operate at 200 kHz (kilohertz). Some are dual-frequency capable, meaning they can use both 50 and 200 kHz transducers. And a few new models are dual-search capable, allowing for both 83 and 200 kHz operation. Typically, high frequency (200 or 192 kHz) sonar units provide the best resolution and definition of structure and targets. They excel at showing minute details of the underwater world. 50 and 83 kHz frequencies have much greater depth penetration capability, but show less definition.
You must match the transducer's frequency to the sonar unit. For example, a 200 kHz sonar unit requires a 200 kHz transducer.
A transducer's cone angle determines its coverage area of the underwater world. The wider the cone angle, the greater the area that's covered. We offer a variety of 200 kHz transducers with either a wide (20°) or narrow (12°) cone angle. The 50 kHz transducers come with a 35° cone angle. The dual-frequency transducers come with both a narrow (12°) 200 kHz and a wide (35°) 50 kHz cone angles. And the dual-search transducers come with both a narrow (12°) 200 kHz and a wide (35°) 83 kHz cone angles.
Generally, use a wide cone angle for fishing shallow to medium depths. The narrow cone penetrates to deeper depths, but shows less fish and structure due to its narrow beam.
The depth capability of your sonar units depends on its transmitter power, receiver, sensitivity, frequency, transducer and transducer installation. Other things that effect depth capability are: water conditions and type(all sonars will show deeper depth readings in fresh water than salt) and bottom conditions.
Types of Transducer Installations
Most of our permanent-mount transducers are designed for high-speed operations. For the best results, the transducer should be placed where a smooth, undisturbed flow of water will pass across the face of the transducer at all boat speeds. Read your transducer's owner's manual before installing the transducer!
<< Transom Mount
The transom-mount transducer is the most popular, and it's generally the easiest to install. The Skimmer® transducer design performs best when it is slightly below the boat's hull. A plastic transducer is recommended on aluminum or steel-hulled boats to avoid potential electrolysis problems.
Mounting the transducer on the transom is recommended for outboard and stern-drive (I/O) powered boats only. Transom mounting is ideal for high-speed operation and models with the "kick-up" feature will prevent damage if the transducer strikes an object.
Make certain that the chosen location doesn't interfere with the boat's trailer. DO NOT mount the transducer directly behind the ribs, or thru-hull fittings. Typically, on aluminum boats, mounting the transducer between two ribs works best. On all hulls, mount the transducer at least one foot away from the engine's lower unit. This helps to prevent air bubbles from the transducer interfering with the propeller.
Periodically wash the bottom of the transducer with soap and water to remove any oil film or growth that may collect. Oil and dirt reduce the transducer's sensitivity and can even prevent its operation.
<< Shoot-Thru-Hull Mount
In this installation, the transducer is bonded to the inside of the hull with epoxy. Ideally, the transducer is placed in the aft third of the hull close to the centerline. The signal "shoots through" the hull with some loss of signal strength. This installation must be made in an area of the hull that is made from solid fiberglass, with no air bubbles or separated layers. If the hull is of multi-layer or "sandwich" construction, you will have to remove the inner layer of fiberglass and the wood or foam core to expose the outer layer of the hull. This type of mount is recommended only with 192 or 200 kHz transducers.
<< Bolt-Thru-Hull Mount
In this type of installation, a hole is cut in the hull and the transducer is mounted through the hull by means of a threaded shaft and nut. If the boat hull has a dead rise higher than 10 degrees, fairing blocks made from wood or plastic must be fabricated so that the transducer will mount in a completely vertical position. The TH-FLW P5 model does not require a fairing block.
On in-boards, the transducer must be installed ahead of the propeller, shaft(s), and engine water intake(s).
If the boat's hull is made of steel or aluminum, use a plastic transducer to prevent electrolysis problems.
<< Trolling Motor Mount
The PD-W "pod" transducer is designed for mounting on an electric trolling motor. It has two slots for a hose clamp (which must be purchased separately). Skimmer® transducers can also be mounted on a trolling motor using the TMB-S trolling motor bracket. It's curved to fit the contour of most electric trolling motors.
Original article from Lowrance