Hey Oz. Since then I've used a new method from some of the kayak guys. I used this method in my kayak and it works great.
The transducer can be mounted to the left or right of the keel without too much of a problem as far as the beam angle. Of course there will be a variance offset to that side, but generally only a small amount.
In the kayaks we use Lexel to adhere to the Polyethelyne hull. In a fiberglass boat I would use 5200 to seal the 4' PVC coupling to the bilge (clean well before hand of course).
Next wedge the transducer into the PVC coupling. Some guys run a screw through the sidewall above the 'ducer to hold it down if it doesn't wedge into place and then seal the screw with more 5200.
Use one of these rubber Quik-Cap's with a small hole to force feed the 'ducer wire through. Most just cut a small X in the cap to get it through.
Next fill the coupling with water. Hold the 'ducer wire and push the Quik-Cap down onto the coupling to seal.
With kayaks being constantly lifted, flipped over and mounted on their sides, the water in the coupling lasts a long time and can be easily refilled. Boats don't get flipped (hopefully) and the water stays permanently.
The Vaseline or Silicone method works good too, but I found the Vaseline gets soupy and runny in hot weather. There is also a chance that you get an air pocket or air bubbles with Vaseline/Silicone. The water eliminates that problem and provides constant readings all the time.
Hope that helps Bud.
