Eagle Electronics 640C, 640cDF manual Shoot-Thru-Hull vs. Transom Mounting

Transom Transom

Transducer centerline

Hull bottom Hull bottom

Align transducer centerline with hull bottom. A dual frequency transducer (left) and a single frequency transducer (right).

There, however, are times when you may need to adjust the transducer slightly higher or lower. (The slots in the mounting brackets allow you to loosen the screws and slide the transducer up or down.) If you fre- quently lose bottom signal lock while running at high speed, the trans- ducer may be coming out of the water as you cross waves or wakes. Move the transducer a little lower to help prevent this.

If you cruise or fish around lots of structure and cover, your transducer may be frequently kicking up from object strikes. If you wish, you may move the transducer a little higher for more protection.

There are two extremes you should avoid. Never let the edge of the mounting bracket extend below the bottom of the hull. Never let the bottom – the face – of the transducer rise above the bottom of the hull.

Shoot-Thru-Hull vs. Transom Mounting

In a shoot-thru-hull installation, the transducer is bonded to the inside of the hull with epoxy. The sonar "ping" signal actually passes through the hull and into the water. This differs from a bolt-thru-hull installa- tion (often called "thru-hull"). In that case, a hole is cut in the hull and a specially designed transducer is mounted through the hull with a threaded shaft and nut. This puts the transducer in direct contact with the water.

Typically, shoot-thru-hull installations give excellent high speed opera- tion and good to excellent depth capability. There is no possibility of transducer damage from floating objects, as there is with a transom- mounted transducer. A transducer mounted inside the hull can't be knocked off when docking or loading on a trailer.

The shoot-thru-hull installation does have its drawbacks. First, some loss of sensitivity does occur, even on the best hulls. This varies from hull to hull, even from different installations on the same hull. This is caused by differences in hull lay-up and construction.

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