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The Transducer:
1) Selecting a fishfinder with the proper frequency, or frequencies, for the specific water conditions where the sonar will be used is one of the most important factors in sonar performance.
Frequency is a measure of how many sonar pulses or signals that the fishfinder sends into the water each second.
i. The higher the frequency (more pulses per second) the higher the detail (target resolution) of the sonar returns.
ii. The lower the frequency (fewer pulses per second) the better the signal can penetrate into the water allowing for use in deeper water.
iii. Graphic of frequency (waves intersecting objects)?
The unit used to define frequency is called a Hertz (Hz).
1Hz = 1 pulse or cycle per second
ii. Marine sonar units use thousands of pulses per second to send the sonar signal.
The scientific symbol for a thousand is derived from the Greek word for thousand, kilo (k).
iii. 1000 cycles per second = 1 kilohertz (1 kHz)
Our fishfinder units operate on any one, or a combination of two, of the following common frequencies:
i. 50 kHz = 50,000 cycles per second
Use: Coastal/Offshore/Deep water use
Pro: Good deep water signal penetration. 50 kHz will penetrate depths greater than 600ft. 50 kHz also gives a wider coverage of the bottom than higher frequencies do.
Con: Not as useful in shallow water due to the lower target resolution when compared with higher frequencies.
ii. 83 kHz = 83,000 cycles per second
Use: Inland/Near Coastal
Pro: Great for shallow to medium depth waters, this frequency is a good compromise between 50 kHz and 200 kHz. Gives a wider cone angle in shallow water for allowing for quicker searches for fish or structure.
Con: 83 kHz does not have the depth capabilities of 50 kHz or the target resolution of 200 kHz.
iii. 200 kHz = 200,000 cycles per second
Use: Inland/Near Coastal
Pro: Great signal resolution makes for easier target separation of bottom structure and fish arches in shallow water.
Con: High frequency that limits the depth range, narrower cone angles (compared to 83 kHz) limit the amount of bottom area searched.
2) Cone angle
Cone angle is the beam angle emitted by the transducer.
i. Image (Use the on the website)
ii. A transducer with a larger cone angle will give a larger search area at the expense of deep water penetration and target resolution, whereas a transducer with a smaller cone angle will give higher target resolution and greater depth penetration.
3) Mounting location/Transducer types
Skimmer™ (Transom Mount): Skimmer transducers are the most common type of transducer used on inland fishing boats and runabouts.
i. Navico offers two versions of skimmer transducers:
50/200 kHz
200 kHz (can be used for 83/200 kHz when used with certain fishfinders).
Picture of install
ii. Pro: Easy to install, good performance for their size. Maintains sonar lock at high boat speeds.
iii. Con: Cannot penetrate deeper waters like larger Thru-Hull transducers can due to their limited element size. Transducer can get damaged from striking objects in the water.
In-Hull/Trolling motor: The other main type of transducer that Navico makes is the puck or pod style transducer that is designed to be mounted in one of two ways:
i. Epoxied inside the hull of the boat:
Picture of install
Pro: There is no need to cut or drill holes in the hull of the vessel to use this method. Less risk of damaging the transducer by impacting items in the water.
Con: This mounting method only works on solid fiberglass hulls. Cannot penetrate deeper waters like larger Thru-Hull transducers can due to their limited element size.
ii. Mounted to the bottom of a trolling motor.
Picture of install
Pro: Allows for the user to see sonar returns closer to where they are fishing.
Con: Risk of damaging the transducer when operating the trolling motor in shallow waters. Can only be used when the trolling motor is deployed into the water.
Thru-Hull: Larger transducers, with larger elements and power capacities, mainly used in coastal/offshore applications. Transducers can be made of plastic or bronze, and are bolted through the hull on a threaded stem.
i. Picture of install
ii. Pro: Great depth capability and target separation compared to other transducer options. Greater range of mounting locations to fit the specific vessel.
iii. Con: Cost more than the other options. Requires a hole to be drilled into the bottom of the boat.