i have spend the whole day today looking inside the game files for a place i could change at what depth the game considers the submarine surfaced or submerged without success.
The closest option i found was called "BelowThisDepthDontReceiveRadio" currently set to "14" i cant believe we woudnt have a similar option for visual contacts for exemple or binoculars use.
I did manage to increase the deck awash depth and increase the time necessary in rough seas for the game to detect the sub as submerged, there must be a option somewhere to increase the depth you need to be to have it consider you underwater... Someone like TheDarkWraith would absolutely know something like this but im afraid this guy doesnt come here anymore.