We decided to build a pirate ship for my grandson...this is how we did it.
I started by drawing out some basic sketches of what I thought would be a cool look and worked out some basic engineering ideas. Our idea was to capitalize on the standard sizes of decking/treated lumber available to minimize waste. We also designed the playground so that all activities could be watched from the back porch of the house (swings, slide, entrance, etc.)
Step 1: Layout
We designed the bottom deck to be 4'x8'. We put together the outside frame first, squared it off, and positioned it where we wanted the playground to go. I then had my son-in-law dig the holes for the 6 each 2x4x8 posts.
After placing the posts in the holes we leveled the frame and attached them together using lag screws. Make sure you drill pilot holes to guide your lag screws and ensure the frame is attached level, square, and securely.
We then poured quickcrete around the posts.
Next we repeated the steps for the second level. We determined the height of the second deck from the recommended height of the slide we purchased at Home Depot (approximately 51"). At first we mirrored the top deck to the bottom deck but soon realized we needed to extend the back of the ship to give us symmetry due to the bow coming off the front. We replaced the 8' sides with 10' sides and let the additional 2' extend towards the back.