For Small Hulls: Survey Ships to Artificial Gravity to Orbital Manufacturing (Small Hulls)
For Medium Hulls: Orbital Manufacturing (Small Hulls) to Orbital Repair to Orbital Ship Assembly (Medium Hulls) (revised, I have seen Orbital Repair offered without Drone Production).
For Large Hulls: Fusion Power Plants to Mega Factories to Advanced Composites to Large Hull Assembly (Large Hulls)
This may not be true, I am playing a new game to test various ideas in this message, that I thought were true from a previous game. Mega Factories may not be needed for Advanced Composites. This message is a work in progress and is subject to correction/revision.
Also size of your (Fleet) Logistics Points almost certainly matters Artificial Gravity to Improved Life Support to Fleet Resupply (+4) to Inter Stellar Resupply Doctrine (+6) to Intermittent Resupply (+8) to Galactic Resupply Doctrine (+10)
Plus according another Player (Halicide in the Discord) Orbital Defense Platform is a + 20 to Logistics Points. Maybe there are some more in the very high parts of the Tech Tree.
You need enough Logistics Point in a Fleet to be able to research and then build Medium, Large, and Huge Hulls. If you can not get a Hull size Tech offered, research better/more Logistics Points. I think that you will need at least one Logistic Points Tech (starting at Fleet Resupply) for Large Hulls and 3 Logistic Point Techs for Huge Hulls.
For Huge Hulls: I think that you will need to build 2 Drones (from Drone Production Tech) in a Shipyard and then expend them to unlock and research a Tech (probably Asteroid Factories) that you will need to get to Huge Hulls, i.e Orbital Deployment Mastery to Subspace Field Creation to Massive Hull Construction.
The Asteroid Factories (and expending the 2 Drones) are the hidden (or additional) requirements for Huge Hulls. Again this is subject to me trying to confirm it again in a new game.
Large Hulls are 10 Slots and 12 Logistics Points and 80 Hit Points and and cost about 600 production.
I have reached and designed Huge Hulls (16 Slots and 24 Logistics Points and 160 Hit Points), although at about 1000 production, never built any.
You can only have one each of the defensive components as well as one each of the fleet support defensive fields per ship. You can build as many weapons as will fit in the number of slots. Plus one each of other (specialty) components. All of which each take a Slot.
Tiny Hulls have 1 Slot and 10 Hit Points.
Small Hulls have 2 Slots and 20 Hit Points.
Medium Hulls have 6 Slots and 40 Hit Points.
Cargo Hulls have 5 Slots and 20 Hit Points.
Also Planetary Mobilization to Centralized Administration to Planetary Invasion to build (Troop) Transports to invade Planets. Only ONE Troop Module (carries one soldier population/citizen) which takes 3 slots, per ship, even if the ship had enough slots (6 or more). Cargo Hull Transports only have 5 Slots or 2 available after the Troop Module.
Many Techs seem to have secondary or additional Techs that have to be researched in addition to the ones shown in the basic Tech Tree that you see in the Tech Descriptions, which comes into play in the above requirements.
Survey Ships is a CRITICAL TECHNOLOGY to the Early Game. It leads to Anomaly Detection which leads to 3 Critical Techs: Artificial Gravity + Subspace Scanning (to use Subspace Streams) + Weak AI which come before the Techs listed above.
You will also need to get Subspace Streaming Tech (comes after Subspace Streaming Tech) to really use them effectively
GC IV is a 4X game and the first X is eXplore. I would recommend taking Survey Ships at your First Opportunity to Research it (probably in your first set of research choices). It enables you to design and build Tiny Survey ships to survey Anomalies and get the goodies from them. As well it leads to a series of MUST HAVE (Fast) Techs. Other Techs in your first set of choices should come AFTER Survey Ships Tech.
Those early Tiny survey ships will only have a Survey Module/component and a Probe Module for Infinite Range, but they are critical to a fast start.
The start of the game Probe design Tiny ship is nice for finding out where stuff is, BUT it can NOT survey any Anomalies.
Asteroid Mining, Space Elevator, Star Bases, etc are nice Techs that you do want, but only after Survey Ships (Tech).
Those Tiny ships Probes and Explorers(Surveyors) will be killed by Pirate snipers, Precursor Ships, and Alien Monsters, so they require careful handling to keep them alive, i.e. run away from anything that can see and then kill them.
I like to design and build Cargo Hull design ships with Infinite Range + Survey Module plus at least 1 Weapon and a Shield/field support to defend against pirate snipers, and either another weapon or a Armor/field support component (to defend against Monsters and Precursor ships).
If those survey equipped Cargo Hull ships can stay alive, you can keep adding more components from exploration results to them to make them faster, longer range, and more weapons/defenses. After awhile they can be decent warships, although a little light on Hit Points, even Drone Bays for 2 Interceptors (per Drone Bay) are very useful. One Drone Bay will add 2 to your Beam Attack and 20 Hit Points. The Cargo Hull designs only start with 20 Hit Points, so even one Drone Bay helps make the ship significantly more survivable. So each Interceptor adds 1 Beam and 10 Hit Points. They do die in combat, but come back over time. It will take a very long time before you can build them yourself, so you get them as just one of the random possible results from surveying anomalies. You need an Extension module as well as the Component module to add the Component to the ship, or you can use Extension Modules to just expand Crew Quarters (Hit Points), Bridge (for 2 speed), or Communication (for 2 Sensor Range).