> For the complete documentation index, see [llms.txt](https://create-deep-seas.gitbook.io/create-deep-seas-wiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://create-deep-seas.gitbook.io/create-deep-seas-wiki/deep-seas/mechanics/sealed-hulls.md).

# Sealed hulls

Everything in Deep Seas starts with one question: is this room sealed? A sealed room keeps the sea out, holds air and takes the water pressure on its walls. A room with a hole in it is just part of the ocean.

## What counts as a wall

The mod scans the inside of your ship and spreads through every cell it can reach. It goes through:

* air,
* the real gaps left by blocks that are not full cubes,
* any block you can walk through: torches, signs, buttons, levers, flowers, kelp, seagrass and so on.

Everything else stops it and counts as a wall.

Blocks that are not full cubes are judged by their **real shape**, never by whether a door says it is open or closed. The sea only gets through where a block leaves an actual gap between the inside and the outside. An open door usually leaves its doorway free, but a door hung sideways so that its open leaf covers the doorway still seals it. The same goes for trapdoors, fence gates, stairs, slabs, fences, walls, panes, bars, ladders and blocks from other mods. Shafts, pipes and other machines running through the hull always count as sealed.

If the scan reaches the outside of the ship, the room is open. If it stays trapped inside, the room is sealed. Each closed space is its own compartment, so a submarine can have several sealed rooms and lose one without losing the others.

{% hint style="info" %}
Opening the outer door of a room underwater lets the sea in through it. Closing it seals the room again. Opening a door between two rooms joins them into one.
{% endhint %}

## Thick hulls

The pressure acts on up to four layers of blocks around each compartment, on the side facing the sea. A hull two or three blocks thick works fine: the outer layer takes the pressure first. If an outer layer gives way it just breaks off. The room only floods or implodes when its innermost layer fails.

## Submarine or boat?

The mod handles every Sable ship one of two ways.

* **Submarine.** A ship with a running [Oxygen Diffuser](/create-deep-seas-wiki/deep-seas/air/oxygen-diffuser.md) or a [Creative Oxygenator](/create-deep-seas-wiki/deep-seas/air/creative-oxygenator.md). Its sealed rooms are full of breathable air, keep their air at any depth and take water pressure. The air is only for breathing: it does not lift the ship. A submarine goes up and down with its [ballast](/create-deep-seas-wiki/deep-seas/mechanics/diving-and-surfacing.md).
* **Boat.** Any other ship floating at the surface. Its open holds stay dry like a real hull and the air in them keeps it afloat. See [Boats](/create-deep-seas-wiki/high-seas/mechanics/boats.md).

A sealed ship with no running oxygen system that ends up underwater does not stay a dry bubble. Once the sea has covered the highest air cell of a room for two seconds, that room floods and stops giving lift. A short plunge is ignored.

## Finding the hole

When a hull will not seal, the problem is almost always one block: an open trapdoor, a torch in the wall, a missing corner.

* The Diagnostic page of the [Onboard Computer](/create-deep-seas-wiki/deep-seas/diving/onboard-computer.md) lists the coordinates of every leak it finds, searching from the room the computer stands in.
* With operator rights, `/submarine findhole` runs the same search from the room you stand in, and `/submarine info` tells you whether the ship is sealed (hermetic) or breached.

## Water inside the ship

The sea is hidden inside sealed rooms per pixel, so you never see water through your floor. This works in any liquid, lava included. A few details:

* Partial blocks walled in on all four sides and underneath are part of the dry volume, so seats, slabs and stairs do not punch holes in it.
* Blocks sticking out more than two blocks above the water (masts, railings) are left out of it.
* WaterWorks breaks this culling for now.