Daughter and son-in-law had replaced a large section of old fence and he saved the old fence boards. Some were rotten to the point of being unusable, but I was able to clean up most of them and had enough for all the decking (floor). I also cut some into narrower pieces for use inside the tree house.

For the ship’s keel (bottom) I used a redwood 2x6 mounted on the diagonals more or less at the center line of the deck. To this I would attach frames for the ship hull. I wanted exaggerated curves for the ship based on examples I saw on the web. I drew a bunch of curves (Bezier curves) using Sketchup and found I could get pretty curvy using 2x6s. My original thought was to design each frame and give the ship curves not only up and down, but also front and back. This turned out to be way too complicated. So all frames were basically the same except for at the front of the boat. And I got very lucky in that when I cut out the hull frame, the drop (the wood that falls away) was quite suitable for the above deck rail. So very little wood was wasted. I used cheap Home Depot fir for the frames.