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Shoot-thru-hull Fish Finders

A fish finder is the one electronic component every angler wants to add to the boat.  Fish finders are available in all price ranges and budgets.  Today’s technology enable manufacturers like Humminbird, Garmin, Eagle, and others to produce finders that are extremely sensitive and reliable.  These sonars have a wide range of features from black and white screens to 256 color displays.  Some have water temperature sensors, vertical bar flashers, fish ID modes and may even be in combination with a GPS.

Fish finder, sonar, or depth finder regardless of the terminology used to describe these units, are very handy.  In some cases they will make the difference between filling the live well or going home empty.  Offshore bottom fishing is but one example.  Most fish school together around structure.  This is particularly true of offshore bottom fish like grouper and snapper.  If the fish finder does not show the presence of these fish on the bottom around the structure, odds are you will waste your fishing time sitting there.

In fresh water the unit is a great tool for keeping track of water depth.  Being able to see the bottom contour may allow for an understanding of fish feeding patterns.  Since many fish feed in shallows, then move off into deeper water, knowing where fish are holding is a perfect place to start the day.  Also, the ability to locate underwater structure is huge.  Bait fish seek out places that provide a degree of protection and predatory fish seek bait fish.

All new fish finders come with complete installation directions and since most installation procedures require the drilling of mounting bracket holes, time should be taken to determine how and where the units components will be located.  This includes the position of the main control/display unit.  Most control/display units are powered by a 12 volt D.C. source so careful consideration should be given to how and from where the unit will receive its power including the type of power connector required and fuse protection.  Next, pre-plan how the transducer cable and power cable will be routed through the boat.  A power cable can generally be shorten or lengthen without effecting the unit’s performance, however, the transducer’s cable must not be cut or tampered with because this would render the transducer inoperative.  Lastly, determine how the transducer will be mounted, this decision largely depends on the construction of the boat.

For aluminum boats or boats constructed of wood, the transducer must be mounted on the outside of the boat’s transom.  Most people simply mount the transducer directly to the boat by drilling holes into the transom and applying a marine grade sealant to prevent leaks.  If the thought of drilling holes into the outside hull of your boat makes you feel anxious, the use of a polymer mounting plate is recommended.  Transom mounted transducers are the most common but in order to ensure optimal performance, while preventing a lose of signal, and lessen the possibility of damage to the transducer, careful consideration must be given to the transducer’s location.  Place the transducer so the trailer will not damage it during loading and unloading of the boat.  Position the transducer as close to the boat’s center line as possible while keeping in mind that if located to near the propeller, turbulence will cause a lose of signal (somewhere between 15 to 24 inch away from the prop should do).  Also, as the boat gains speed, turbulence will be created directly aft of strakes or ribs, even a roll of rivets, so do not mount the transducer directly behind these areas.

Some transducers are specifically designed for mounting inside the hull of boats constructed of fiberglass composite materials eliminating the necessity to drill holes in the transom.  In order for the transducer to shoot the sonar signal through the hull, the transducer must be located in an area where the hull is a single solid fiberglass layer without any laminated fillers or open air spaces.  For most fiberglass boat this area is easy to recognize, generally the very aft section near the drain plug and bilge pump.  Also, since the transducer will be permanently fixed in place by a slow-curing epoxy, it is absolutely necessary to test the operation of the unit.  Simply complete all installation steps including routing the transducer to its desirable location but DO NOT mount the transducer in place.  After the boat has been launched in a near by water way, fill the aft section of the hull with just enough water to submerge the transducer than test the unit‘s operation.  If the unit operates as advertised, shoot-thru-hull transducer installation can proceed.  Once the transducer has been fixed in place (remember to use only a slow-cure epoxy), water, gas, or oil spillage will not affect the performance of the unit, however, if the unit is equipped with a surface water temperature senor, only the hull temperature will be indicated.


shoot-thru transducer

Shoot-thru-hull mounting offers good performance at high speeds and often better protection against transducer damage.  Transom mounts may provide a small degree of greater sensitivity and has advantage of easy transducer replacement if necessary.  The transducer location and installation is the most critical step of all, so carefully read and follow the manufacturers recommend procedures to ensure peak performance.

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