That's John behind the ladder. Hi, John!
The thing with nuts sticking out is the rudder shaft log. The rudder will hang, the short tiller goes through the transom under the swim grid. John has made it so that he can undo the bolts from outside if he wants to access the rudder shaft. The bolt heads on the inside are welded to oversize washers that are held from turning by screws through them. John thinks of everything. 😎
The platform, which came with the boat, is fibreglass with a balsa core deck. John replaced the centre knee with two knees, one either side of the shaft log. Should hold a good sized elephant. I mean elephant seal.