Trev, I had the fan above the heat sinks, sucking air out of the box.
I did drill many small holes in the enclosure, enough so that the fan motor wasn't working hard.
I have ditched the fan for now and have the board in a larger box cooling naturally.

I am looking for a board that can supply the 2 x 50W transducers easily.


Happy is he who penetrates the mystery of things.