Re: Arriva 2450 Fishfinder/Chart Plotter Install
Before you install the transducer inside the hull, you should ensure that it will be shooting through a solid laminate and in an area of smooth water flow under the hull, ie not astern of any through-hulls or other fittings.
To check the proposed location, place the transducer into a plastic bag of water, wet the outside of the bag and the interior of the hull.
With your boat in deep water, close to the maximum depth you will want to read, position the bag against the hull while someone else observes the display. Move the bag around until you obtain the best signal then mark the spot.
Dry the hull and put a good sized glob of silicon on the hull. Place the transducer into the silicon at an angle and then bring it to the vertical while pressing down. The objective is to squeeze out any air bubbles in the silicon.
Now take your boat on a high speed run to check the installation.
I have use this procedure on a number of vessels. The only negative is you may lose a little on the maximum range.
. You can also silicone the factory transducer inside the engine bay or where ever. 
