you wish for the transducer to be flush with the bottom of the pontoons, you should use a bracket that mounts the transducer to the center of the front of the deck, and even with the bottom of the pontoons.

3. Transom Mounting the Transducer.

A) Point Forward
The entire face of the transducer must be below the hull. me back of the transducer should be 1/8'-1/4' lower than the front. It should be placed within the center third of the transom. approximately 10 - 12 inches from the keel so it won't be in front of the prop.

B) Flush Mounted

The junction between the transducer and hull should be filled in with silicone sealer or a caulking compound to provide a smooth transition between the transom and the transducer housing. The back of the transducer should be 1/8'-1/4' lower than the front. It should be placed within the center third of the transom for the smoothest flow of water.

NOTE: Flush Mounting should not be used on hulls that have
             a dead rise greater than 10 degrees.

4. Shooting Through the Hull.
Sonar will shoot through a single layer of fiberglass only. If your hull has some type of core material, you should cut or drill through it until you reach the outer layer of fiberglass. This will allow you to epoxy the transducer to this layer of fiberglass.
Shooting through the hull requires a good bond between the face of the transducer and the hull. When gluing the transducer to the hull, follow all of the manufacturer's guidelines to insure a good bond.

Bonding Agents:
Epoxy is the best adhesive for bonding the transducer to the hull, but it
has to be a marine grade' epoxy that will stay hard when wet.
Fiberglass Resin will provide a good bond if mixed properly and allowed to dry completely. To ensure a good bond, the face of the transducer should be sanded lightly with fine grade sandpaper.

Silicone will not provide a good bond and should not be used.

Any material that is son or porous will not provide a proper bond. Any material that contains metal as a strengthening agent will attenuate the signal.

5. Mounting Through Hull
With mount through hull installations, the transducer should be mounted ahead of prop(s) or water intakes. It should also be coated with a non-metallic anti-fouling paint. Metal based paints do not work.

6. Trolling Motor Mounting
Shallow water is the most difficult for sonar to operate in. The closeness of the bottom to the transducer can cause the sonar to lose its lock on the bottom. It is best to put the trolling motor down in the water and turn the sonar on while the boat is still in 6-8 feet of water.

Another possible hazard to mounting the transducer on the Trolling Motor is electrical noise. The Variable Speed Control - Battery Save feature type trolling motors generate a great deal of electrical noise. Having the transducer mounted on one of these motors can increase the effect of the electrical noise on the sonar.

7. Transducer Cable Routing
Whenever possible, route the sonar's power and transducer cables away from other boat wiring. This will help prevent electrical noise from the boat's electrical system from interfering with the sonar.