I don't think that's a step. I am guessing here (Based on the "kicker bracket" on the swim platform) that that is actually a device to troll with the main engine. I think maybe it's called "The Happy Troller". Seriously. I have seen them advertised.
The generic name for what I believe that to be, where I come from, would be a trolling plate. Google knows where to find one. I even checked just to be sure and Google said "Heck yeah man. I know all about that sh*t!" :yo: