Structural module

Structural Modules are a category of module consisting of modules designed to provide a general increase in health and structural integrity to an airship or landship, and modules designed solely to serve as connections between other modules.

Small Keel
A solid wooden keel to reinforce the ship.

Small Keels are 1x5 modules which add a bonus to the health of the other modules on ship and reduce the structural stress of a large ship.

Large Keel
A massive wooden keel that adds a great deal of structural integrity.

Large Keels are 1x9 modules which behave similarly to Small Keels, but give a much larger bonus than a Small Keel, even when considering the near doubled length of a Large Keel.

Grand Keel
Crafted from the trunk of a giant tree, this Grand Keel provides a massive boost to the ships structure.

Grand Keels are frankly massive 2x14 modules which require the Great Forest bonus to build in Strategic Mode. Similarly to the Large Keel in relation to the Small Keel, it provides a disproportionately larger increase over the Large Keel in all areas.

Corridor
Allows crew to move through the ship rapidly.

Added in 0.9.?/v10, the corridors are 1x1 modules that let crew move through them like the corridors with ladder, but limited to the right or left.

Corridor with ladder
Allows crew to move through the ship rapidly.

Corridors with ladders are 1x1 modules that let crew move through them nearly twice as fast as most normal modules and contain a ladder so crew can move into modules above that may otherwise be unreachable or require a long delay.

Deck
Decks let your crew move at high speeds, but offer no protection.

Decks are 1x1 modules that allow crew to move even faster than through Corridors, clocking in at around three times the movement speed of most normal modules. However Decks are external modules, thus crew are at high risk from a well-aimed shot from an enemy airship.

Fire Door
''A reinforced fire door to slow the spread of fire down the ship's corridors. It also slows the crew down a little''

Fire Doors are 1x1 modules that share the easy connection properties of Corridors, but instead of allowing for notably faster movement, it instead offers a high level of structural and fire resistance.

Strut
A sturdy and lightweight framework for reinforcing your construction.

Struts are 1x1 modules that provide more bonus health to adjacent modules than normal. Outside of that they can be used to connect external modules like Rams and Suspendium Tanks to the rest of the ship while putting a bit of space between them.