I am pretty sure it is a knotmeter transducer. I have a Signet knotmeter in my Pearson 10M that is removable with the metal bracket on top that allows for the removal. The screwable lid below the metal bracket is what screws the transducer on to the tube and hold it there water tight.
There’s a compass, tilt meter, and I think there is a knotmeter in the middle. OK, that splains things lots for me.
Be careful while removing the transducer while in the water! You get a good gush and run a risk of sinking your boat if not plugged. I use a similar shaped plastic plug to cover the hole while I clean the transducer that has been removed. After cleaning I pull out the plug (which also has a similar screw type head) and replace the transducer. This is common design for knotmeters.
I won’t touch it, period.
If you don't have a meter, how do you measure boat speed on your boat?
Haven’t had this boat in the water yet. It’s been trailered since 2008.
GPS? Technically there are only two wires coming out of the Knotmeter transducer. The cable is shielded.
I’m actively shopping for a thru-hull transducer type Depth Meter. Reasonably priced one in the 2010 West catalog. Maybe I can install its transducer on the opposite side of the boat, exactly in the same location as this transducer. Would be an excellent place, right below the starboard salon.
I do have a hand-held GPS Magellan that I was going to hook to a computer to use as a chartplotter, using the Polar View software/charts. If that works fine, I won’t have to buy a dedicated chart plotter.
Thanks for your insights guys. I built a one-pager punchlist of things to do last night. Going to be a very busy weekend.