Installation of Raymarine ST40 Speed and Depth Transducers

I wanted to add speed and depth indication to my S2.  I looked at several different options and chose the Raymarine ST40 for it's features, size and price.  I found a set of transducers on eBay that matched the display so I was in business.  

I found the Raymarine ST40 display on sale at Overtons for $180.  The bidata display shows two readings at once. The transducers actually pickup depth, speed and water temperature. 

The hull of the S2 6.9 is about 9/16 of an inch thick cored with 3/8 inch balsa.  This construction makes for a extremely solid hull. The outer skin seemed to be about 1/8 inch thick and the inner skin was thinner at about 1/16 of an inch.  This is a shot of the core taken from one of the holes drilled out near the keel.

When cutting in a thru hull it is important to know if your hull is solid fiberglass or if it is cored with wood or foam.  If your hull is solid fiberglass simply cut the hole all the way through and install the thru hull with 3M 4200. 

The picture shows the proper preparation for a thru hull fitting in a cored hull.  The hull of the S2 is cored with basla wood. If a hole was simply cut in the hull it may leak into the core and and delaminate the hull. The proper way to prepare the thru hull is to cut the inside core out a little bigger than the thru hull fitting. 

 In my case the transducers are 2 inches in diameter.  I cut the inside out with a 2 1/2 hole saw.  I then filled the hole with fiberglass resin to seal off the core and then drilled it out with a 2 inch hole saw.  The instructions recommended that the transducers be installed ahead of the keel and on the flattest part of the hull not to exceed 10 degrees.  They also recommended that they should not be place in front of each other because it might cause turbulence and affect the readings.

I am just waiting for a warm day to install the transducers. To power the ST40 display you simply need to run a red wire to the positive lead and a yellow wire to the negative lead. I am still trying to figure out where to install the display.  I am not sure I want to cut more holes in the bulkhead so I am considering alternate locations. Stay tuned.