Ballast pond
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Wooden ships used to have their hulls waterproofed using tar. To facilitate the application of tar below the waterline, shipyards built a square ballast pond in shallow water with an entrance port on one side. A ship would enter the ballast pond and be tied to one wall. Then on the low tide, the ship would lean on one side to allow the tarring. On the next tide, the ship would be tied to the opposite wall to complete the job.