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Old 09-27-2014, 07:58 AM   #16
RT Firefly
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City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 13,145
When I purchased our Garmin 531S (I think) GPS/sonar I had the option of a transom mount, shoot-thru the hull or thru hull (for extra cost) transducer. Like many, not wanting to have the boat hauled for 'ducer installation I opted for the shoot thru unit. It is similar to this:

I caulked the base to the hull and filled it with mineral oil. Works fine for what I want which is simply an estimate of how much water is generally under the keel. I probably lost some sensitivity but I didn't really care. Using the charts and the "trend" of what the bottom is doing is good enough for me.
As a matter of fact I have done this with 2 units. One for pilot house and one for FB. I currently have 2 redundant thru hull units and one old style paddle wheel speed unit which will be removed, probably next haul out.
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