There are several different methods you can use to mount your fish finder. In this article mounting refer to attaching the transducer to your watercraft-boat, kayak, float tube, etc. "Mounting" your fish finder display is a separate topic. The common methods are: transom mount, through hull, and portable mounts. There is also a "Shoot Thru" hull mounted transducer, but this type is less common.
As the name suggests, a transom mount model mounts on the transom of the boat. The best mounting location is at the bottom of the transom, with the transducer face (bottom) parallel or nearly parallel to the transom itself. All major manufacturers recommend that installation be completed out of the water. In order to minimize turbulence and aeration around the unit, do not mount the transducer along strakes, behind through hull fittings or other hull irregularities as they can cause unusual disturbances around the transducer and cause improper readings. Thru Hull units, when properly installed, typically offer better fish detection and overall performance than other mounting methods. Since this mounting method requires drilling or cutting a hole through the hull, all through hull installations should be completed while the boat is in dry dock. As with transom mounted models, through-hull transducers should be completely submerged in water with good water flow through the unit. Objects such as strakes, fittings and propeller wash can disturb the water flow and cause inaccurate readings. Work to avoid any areas where the water flow will be uneven or disturbed. To eliminate leaks it is imperative to seal any holes between the transducer and hull. It is generally best to have a professional install through through-hull model.
Portable fish finders are the easiest to install, if they need any installation at all. Some portable fish finders have a transducer with a suction cup mounting system. Just take these models and stick the suction cup to your boat, kayak or float tube benefit the water line so that they are completely submerged. Again, make sure the transducer can have free, uninterrupted water flow. Humminbird also makes a line of portable fishfinders that use a clamp to attach the entire fish finder to your watercraft. The transducer is at the bottom of the fish finder shaft and will be submerged as all transducers should be.
There are also some portable fish finders that need no mounting at all. The Humminbird SmartCast series has a remote sensor fish finder that is wireless. Simply attach the sensor to your fishing line and cast it along with the bait. It will provide signals back to the display so you can see if there are any fish near your line. This type of fishfinder is an excellent choice for shallow water fishing.
The last mounting method is the "Shoot through" transducer. Unlike through-hull models, shoot through models do not require a hole in the boat's hull. Instead the unit is placed inside the hull and transmits and receives signals from there. This type of fish finder works only with fiberglass hulls and as with other methods, placement is critical. Usually a flat spot in the aft bilge area is the best location, but check with a professional.
There are several ways to attach a shoot through model. They can be bolted on or some can be fiberglassed or epoxied to the hull. There are also some shoot through models that are encased in a special enclosure. A professional can help you choose the right method for your fish finder and your boat.
Fish finder mounts can be difficult depending on the type. If you have any doubts about how to mount your model, it is always best to get professional help.