Like all of us have carbon fiber hulls. LMAO!! hil hil hil RealityMount them under the dash board, they must remain pointed up for the best signal reception. If your hull is carbon fiber reinforced, this will weaken the signal going thru the hull. Try a few different areas, to find the best suited location, there is no need to mount them on the top of the deck.
total over kill. good mandevilMy boat has a bulkhead up front. I took a sheet of 1/8" aluminum sheet, put two 45* bends in it, then welded a piece of 3/16" flat bar and welded it on the angle for support. Bolted that to the bulkhead and black RTV'd the antennas to the top, facing up.