I'm getting really interested in the thought of making and trialling a splash plate... with about 60Nm of splash experience under my belt now.
I looked under the engine cowl when the family were exploring a beach mid trip yesterday and the splash is getting up through the outboard lower cowl drain holes enough to put beads of water on the plug leads and coils. This is with the maximum thickness shim (30mm or so) before the metal pad needs lifting. No misfire yet but the potential is there.
Other thing I noticed is the splash I'm referring to is when the boat seems properly trimmed to me... re people/weight distribution. Last night though daughter was cold with the headwind on the plane so got down to sit inside the bow facing the stern which made the boat feel a bit nose down to me.... however the splashing was reduced to a mini rooster tail which was missing the outboard and not splashing inside.... quite acceptable.
That long plate linked above is not quite as neat as the one pictured by chipko on post 7 here... Old used Aerotec impressions.
but it does have the advantage of avoiding drilling yet more holes in the transom.
Another thought... and you're better than me at forum searches Max... didn't someone posts ages (years?) ago about making a piece that they cable tied to the troublesome lumpy bit of the outboard that's causing the splash... a sort of wing leading edge idea so it cut through the water better??