Underwater Bases

Blocks for a dry, permanent base on the sea floor.

Clear the space first with a Bubble Anchor, wall it in, and set the anchor to leave air when it ends. These blocks keep the room dry afterwards.

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Pressure Hatch

A steel door with a porthole, two blocks tall. Open and close it by hand or with redstone.

• The sea never comes through it, open or closed, so you can swim in through an open hatch and the room behind it stays dry.
• Every time it closes it pumps out the water on both sides of it, as long as that water is a small pocket: the water you dragged in, a flooded doorway, a leak. Up to 64 blocks of connected water are cleared at once.
• Water that is part of the sea, or a flooded room bigger than 64 blocks, is left alone, so closing a hatch never drains the ocean outside.

Placing a hatch in water clears the two blocks it fills, so you can fit one straight into a flooded doorway.