Beware fitting cheap plastic transducers thru "wood" hulls. I believe both NASA and Airmar (specialist US based manufacturer of sensor heads, supplying much of the world's sounder manufacturers) specifically warn against this, due to movement in the wood and its potential to cause leaks or worse, crack transducers. They propose a fancy bronze hull fitting (VERY expensive, and probably heavy?)
But then, not sure they mean epoxy ply wood? Perhaps JMs experience reflects this?
I know NASA clipper struggles a bit with placement thru hull in a BRe, mine was very much trial and error and then is still not ideal.
On my Baycruiser, it's worse. The NASA thru hull fails completely to penetrate in areas of Divinycell foam laminate, and only just (and very unreiably) works thru the solid grp areas of the hull.
Googling gives good info from Airmar which says laminates and voids within ply or glass hulls will cause thru hull problems.
My fancy Raymarine plotter/sounder/sonar screen unit having failed, I'd planned to use the NASA as a cheap/temporary sub. To no avail. It's just too unreliable, as fitted to my BC 26.
I've had to fit a Raymarine sounder, but at least with a new sensor I could reuse the existing thru hull. Set up was over twice the price of NASA, and smaller display. As a plus, it gives me water speed and temperature from the triducer head, and it can be removed for cleaning whilst afloat.
Consequently, if you are feeling brave, I have an Airmar spare plastic thru hull fitting potentially going cheap (triducer assy was £180) if you fancy trying that?
However, BR20s seem to be able to mount sounder heads up inside the forefoot of the board case, and that apparently gives good results. I didn't discover this until after fitting my NASA internally.
