Accessing your shipyards:
Step 1. Open your housing items ( the little bed icon; what you use to decorate. )
Step 2. Open your storage ( goes to your attic).
Step 3. On the far top left of the storage page, choose the backpack icon.
Step 4. When your backpack opens, click on the ship you wish to place in the shipyards, then -
Step 5. At the bottom of the same page, you'll see a ship icon ( that's your shipyards ) click on that and your ship will appear near your island.
To reclaim a ship just reverse steps 4 & 5.
I hope this clears it up for you.