Depth Finder Help!!!
Moderators: bman, Chalk, Tom Keels
Depth Finder Help!!!
I am in the process of re-rigging my boat and need some input. I have a 23' WAC and am unsure if I should go with a thru-hull transducer with my new unit of a transom mounted one. Any one know of any pros or cons on this idea and your help is appreciated.
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Tidedancer
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Transducers
The transducer is the sonar unit's "antenna". It converts the electric energy from the transmitter to high frequency sound. The sound wave from the transducer travels through the water and bounces back from any object in the water. When the returning echo strikes the transducer, it converts the sound back into electrical energy which is sent to the sonar unit's receiver. The frequency of the transducer must match the sonar unit's frequency. In other words, you can't use a 50 kHz transducer or even a 200 kHz transducer on a sonar unit designed for 192 kHz. The transducer must be able to withstand high transmitter power impulses, converting as much of the impulse into sound energy as possible. At the same time, it must be sensitive enough to receive the smallest of echoes. All of this has to take place at the proper frequency and reject echoes at other frequencies. In other words, the transducer must be very efficient.
Crystal
The active element in a transducer is a man-made crystal (lead zirconate or barium titanate.) The chemicals are mixed, then poured into molds. These molds are then placed into an oven which "fires" the chemicals into the hardened crystals. Once they've cooled, a conductive coating is applied to two sides of the crystal. Wires are soldered to these coatings so the crystal can be attached to the transducer cable. The shape of the crystal determines both its frequency and cone angle. For round crystals (used by most sonar units), the thickness determines its frequency and the diameter determines the cone angle or angle of coverage (see Cone Angles section.) For example at 200 kHz, a 20 degree cone angle crystal is approximately one inch in diameter, whereas an eight degree cone requires a crystal that is about two inches in diameter. That's right. The larger the crystal's diameter - the smaller the cone angle. This is the reason why a twenty degree cone transducer is much smaller than an eight degree one - at the same frequency.
Housings
Transducers come in all shapes and sizes. Most transducers are made from plastic, but some thru-hull transducers are made from bronze. As shown in the previous section, frequency and cone angle determine the crystal's size. Therefore, the transducer's housing is determined by the size of the crystal inside.
There are four major housing styles in use today. Thru-hull, shoot-thru-hull, portable, and transom mount.Thru-hull Transducer
Thru-hull transducers are inserted through a hole drilled in the hull. These typically have a long stem that slides through the hull and is held in place with an equally large nut. If the hull is flat, this is the extent of the installation. However, if the transducer is to be mounted on one side of a "vee" hull, then a fairing block must be made from wood or plastic that allows the transducer to be mounted vertically. Thru-hull transducers are typically used on inboard powered hulls so the transducer can be mounted in front of the rudders, propellers, and shafts.
Shoot thru hull transducerShoot-thru-hull transducers are epoxied directly to the inside of fiberglass boat hulls. The sound is transmitted and received through the hull of the boat - but at the cost of some loss of sonar performance. (You won't be able to "see" as deep with a shoot-thru-hull transducer as one that's mounted on the transom.) The hull has to be made of solid fiberglass. Don't attempt to shoot through aluminum, wood, or steel hulls. Sound can't pass through air, so if there's any wood, metal, or foam reinforcement, it must be removed from the inside of the hull before installing the transducer. Another disadvantage of the shoot-thru-hull transducer is it can't be adjusted for the best fish arches. Although there are disadvantages to a shoot-thru-hull transducer, the advantages are considerable. One, it can't be knocked off by a stump or rock since it's protected inside the hull. Two, since there is nothing protruding into the water flow, it generally works quite well at high speed if it is mounted where a clean laminar flow of water passes over the hull. Three, it can't be fouled by marine growth.Portable Mount Transducer
Portable mount transducers, as their name implies, temporarily mount to a boat. These transducers typically use one or more suction cups to hold them to the hull. Some portable transducers can also be adapted to electric trolling motors.
Transom Mount TransducerTransom mount transducers are installed on the boat's transom, directly in the water and typically sticking a little below the hull. Of the four housing types, the transom mount is by far the most popular. A well designed transom mount transducer (like the HS-WS Skimmer®) will work on almost any hull (except inboard powered boats) and at high speed.
The transducer is the sonar unit's "antenna". It converts the electric energy from the transmitter to high frequency sound. The sound wave from the transducer travels through the water and bounces back from any object in the water. When the returning echo strikes the transducer, it converts the sound back into electrical energy which is sent to the sonar unit's receiver. The frequency of the transducer must match the sonar unit's frequency. In other words, you can't use a 50 kHz transducer or even a 200 kHz transducer on a sonar unit designed for 192 kHz. The transducer must be able to withstand high transmitter power impulses, converting as much of the impulse into sound energy as possible. At the same time, it must be sensitive enough to receive the smallest of echoes. All of this has to take place at the proper frequency and reject echoes at other frequencies. In other words, the transducer must be very efficient.
Crystal
The active element in a transducer is a man-made crystal (lead zirconate or barium titanate.) The chemicals are mixed, then poured into molds. These molds are then placed into an oven which "fires" the chemicals into the hardened crystals. Once they've cooled, a conductive coating is applied to two sides of the crystal. Wires are soldered to these coatings so the crystal can be attached to the transducer cable. The shape of the crystal determines both its frequency and cone angle. For round crystals (used by most sonar units), the thickness determines its frequency and the diameter determines the cone angle or angle of coverage (see Cone Angles section.) For example at 200 kHz, a 20 degree cone angle crystal is approximately one inch in diameter, whereas an eight degree cone requires a crystal that is about two inches in diameter. That's right. The larger the crystal's diameter - the smaller the cone angle. This is the reason why a twenty degree cone transducer is much smaller than an eight degree one - at the same frequency.
Housings
Transducers come in all shapes and sizes. Most transducers are made from plastic, but some thru-hull transducers are made from bronze. As shown in the previous section, frequency and cone angle determine the crystal's size. Therefore, the transducer's housing is determined by the size of the crystal inside.
There are four major housing styles in use today. Thru-hull, shoot-thru-hull, portable, and transom mount.Thru-hull Transducer
Thru-hull transducers are inserted through a hole drilled in the hull. These typically have a long stem that slides through the hull and is held in place with an equally large nut. If the hull is flat, this is the extent of the installation. However, if the transducer is to be mounted on one side of a "vee" hull, then a fairing block must be made from wood or plastic that allows the transducer to be mounted vertically. Thru-hull transducers are typically used on inboard powered hulls so the transducer can be mounted in front of the rudders, propellers, and shafts.
Shoot thru hull transducerShoot-thru-hull transducers are epoxied directly to the inside of fiberglass boat hulls. The sound is transmitted and received through the hull of the boat - but at the cost of some loss of sonar performance. (You won't be able to "see" as deep with a shoot-thru-hull transducer as one that's mounted on the transom.) The hull has to be made of solid fiberglass. Don't attempt to shoot through aluminum, wood, or steel hulls. Sound can't pass through air, so if there's any wood, metal, or foam reinforcement, it must be removed from the inside of the hull before installing the transducer. Another disadvantage of the shoot-thru-hull transducer is it can't be adjusted for the best fish arches. Although there are disadvantages to a shoot-thru-hull transducer, the advantages are considerable. One, it can't be knocked off by a stump or rock since it's protected inside the hull. Two, since there is nothing protruding into the water flow, it generally works quite well at high speed if it is mounted where a clean laminar flow of water passes over the hull. Three, it can't be fouled by marine growth.Portable Mount Transducer
Portable mount transducers, as their name implies, temporarily mount to a boat. These transducers typically use one or more suction cups to hold them to the hull. Some portable transducers can also be adapted to electric trolling motors.
Transom Mount TransducerTransom mount transducers are installed on the boat's transom, directly in the water and typically sticking a little below the hull. Of the four housing types, the transom mount is by far the most popular. A well designed transom mount transducer (like the HS-WS Skimmer®) will work on almost any hull (except inboard powered boats) and at high speed.