With the panel removed there are 4 nut plates which need to be removed. They're riveted on with flush rivets so there is no tool to help locate the drill except to carefully center punch the rivet. With AD rivets it's at least easy to center the punch mark in the dimple on the head. I find a regular center punch and hammer work better than a spring loaded center punch.
Here is a good picture of using the modified diagonal cutter to grip the upset end of the rivet to wiggle it out.
The next step was to create templates for forming the new panel bends. I made 2 corrugated templates for each end. One is based on the free shape of the panel and the other is the shape of the bulkhead at each end. My goal will be to form the new part between these 2 limits.
Now I can flatten the panel to use a pattern for the new panel. I carefully hammered out the dents better. There is no way to completely remove the dents. If needed the worst areas could be cut out to allow the rest of the panel to be flattened without distorting it.
I clamped the panel to the deck railing with a 2x4 and used another to push on the free end of the bend. You just keep re-positioning it and working the bend out in small increments. It doesn't have to be perfectly flat but close enough that it can be clamped to the new aluminum sheet while keeping the panel flat to duplicate the holes and cut lines.
With the panel flat one thing I hadn't thought about was obvious. I would have laid out the panel so the grain ran perpendicular to the center line of the panel. You can see from the printing it runs perpendicular to one edge to minimize waste.
I measured the thickness of the aluminum to buy the new material. It's nice to see on the inside that the original material was 0.032" thick 24ST (now called 2024-T3) Clad Aluminum. Alcoa created Alclad 2024 aluminum in 1931. Before that Duralumin 2017-T4 was the go-to structural aluminum. As a result they haven't made 2017 sheet in years.
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