[FishStretcher]

I took some measurements. My dry joint riser elbow is 7-1/2" above the deck.

That makes it 9-1/2" above the bottom of the scupper. On my boat, the scum line is another 2.5" below that, and the chine is another 2.5"

Figuring that fully loaded, the scuppers might be just at sea level, then I have 9-1/2" from the riser to the ocean. And 12" sitting at the dock.

Looks like I need at least a 4", and really more like a 6" riser extension. Thankfully, it looks like there is room. Although the 6" is starting to get close.