thanks,
the thickness is exactly 3/8" solid.
if it was thicker 1/2" or 3/4" i would have skipped the backing block, but the tranducer itself has some weight to it, and wanted to support it and not stress the hull to much...
i'm not too up on the 200/50, but i think it goes with the size of the "cone" it produces, one is better in deep water than the other...but i know this is a 600watts unit and I plan to go with the new furuno fvc 620 fish finder which is also 600watts...