I've visited Boat Lagoon and the Phuket Marina many times. The marina is the starting place for my Pizza Run to Coconut Island.
It's also a very good place to go Yacht spotting. But the yacht in dry-dock really are too big to see, you see the hull, and not much else. So time to take to the sky for a better look!
There's quite a few marinas on this, sheltered, side of the island, you can see another one in my earlier drone video.
Royal Phuket Marina is the posher of the two, Boat Lagoon is more practical, with a better supermarket. I fly from the north bank, where's there's some public piers for the fisherman to do boat repairs.