Naval style spaceship design
This is a guide for ship design in a roleplay context mostly to do with art style with both 3d designs and traditional 2d art, (from someone who does not do art) the goal in essence is to apply some sense to how you could use different layouts in turrets and basic design styles within ships to help improve aesthetics.
Section 1: Hull form and ways to denote class
Width: Width is a factor in general ship design often overlooked for most purposes. People usually go with very thin hulls for their ships relative to the size of its guns, generally when making large ships with heavy gun turrets a large width is advised as it adds storage and volume compared to its length.
As you can see here this is a model of an iowa class battleship as you can see with the rather large gun turrets they are dwarfed by the hull, this is for range ammo capacity and crew additionally ships with large width can handle recoil effects far better and generally are slower. The slow aspect is due to traditional naval ideas and the fact that water is very dense even though there is a distinct lack of water in space, when you're basing your spaceships off of naval vessels you take into the consideration both naval design as well as ship design.
Length: Length is a standard way to tell the general size of most ships however it's far more than that in terms of how it's used in design, length in general is a method of adding volume that does not increase your frontal surface area. While on naval vessels this was to reduce how much water you would go through and as such reducing your drag relative to its width, and allowing you to add more supplies or engines for range and speed and such in the context of space its an increase in size that can't give you larger guns (excluding spinal weapons) however it does give you more area to place more weapons and general volume.
This is a fletcher class destroyer as you can see its guns are relatively wider compared to the size of the vessel, and there's far more turrets given they have less guns on them and as you might guess its a destroyer and it's quite fast. That's because it's small and you can put all your engine power forward in general if you want a fast light ship a long thin design makes it seem much more believable, it's also a very important aspect on carriers as since your not adding width you can store more things like planes generally making carriers quite long.
Height: Height in a sense is very close to width, they both increase surface area forwards and are both used for purposes quite close to each other, however height is needed overwidth most of the time for space ships the reason being?
This is a 16 inch naval gun turret and as you can see however impressive the guns may look from the top and sides, internally their height is by far the most impressive thing about them the cannons encased in giant rotating sections with elevators bringing ammo up and down to supply the turrets. This is a massive factor determining design as in space you can do something quite funny that you can't pull off with a water based ship.
Credit to @MrBalkenKreuz for the alsace class battleship
As you can see this ship has guns on its top and bottom. This is very very tempting in space and would be very good for things such as secondary batteries, however it's important to take into account a ship's height for this factor. You have to reduce your gun size otherwise your turrets simply won't be able to coexist on the same plane so if you want to go for the largest gun layout, you need to stick to one side of the ship to comprise the main battery however this might not be needed with spinal guns and the like. Height however works inverse to width in terms of stability where a very wide ship can maintain itself relatively easily under recoil, a tall ship might flip over its mass acting like a lever pulling it with immense rotational energy.
Section 2: Ship layout
Broadside ships: Broadside ships are generally traditional battleships such as ones of the dreadnaught era, designed to fight in lines using the turning turrets to allow for wide firing angles and firing at targets with many large gun turrets. These are designed to maximize firepower to the side while still keeping the large guns to either side, making them quite capable in number however they struggle in charging and frontal attacks.
Direct fire ships: Direct fire ships follow layouts specifically to fire in a single direction; these often have less total firepower then broadside ships, (unless spinal guns are in play) however they are much harder to hit and can be armored more in their respective direction due to low surface area. They are very good at direct attacks however can be flanked and destroyed easier from small ships, or swarms of fighters if their anti aircraft weapons are not well built.
Firing arks/gun spam: Firing arcs are often very important to ships when defining against small craft and often mid sized vessels the quality of guns able to target is far more important than the amount of guns, well built AA grids having many secondary guns in towers able to hit all over the ship with larger dedicated positions. When you put too many guns you start to run into questions like, where do I store my ammo? How do I have the space for all this machinery? How much does it cost to make 3000 machine guns? Make no mistake these ships are often frowned upon in the community and should be avoided, they do not look very good and often are used to justify immensely annoying ships.
Weapons and armor how to employ them
Armor design: Naval armor is a complex topic however generally a ships armor is designed to stop damage as well as increase the raw durability of a vessel, any decently sized weapon will break through armor of all but the strongest ships if it needs to, a 12 inch sabot round fired out of a low relativistic railgun is virtually impossible to armor against. However to the same degree such a round would go clean in and simply make a small hole in the side it lacks the damage to hurt a large ship and will only annoy it, for protections sake armor is used to stop point defense weapons or mid range guns from shredding your vessels and as to stop longer range guns you need to drain their energy and direct it.
As those charming fellows will tell you "Captain, there's a new window here!" a battleship grade shell harmlessly passes through this ship, in this case reducing armor has helped with durability, when you consider it you can break armor into a couple key factors.
Your ability to stop rounds full stop with combinations of ERA and composites, your armors ability to resist heat such in the case of lasers or explosions, and finally your armors ability to improve the ships damage resistance as while you can't stop a multiple dozen ton shell with a nuke in it completely you can have the explosion clash against your ships hull propelling outwards and deflecting the explosion massively reducing its effect compared to ripping the ship to shreds as its structure can't handle the influx of energy.
Close range weapons: Close range weapons are used to get ships out of your face quite simply, they are absolutely needed however are often neglected compared to heavy guns and point defense, these include things like casemates and mid range turrets. They are usually very high fire rate guns optimized to work at close range where they aren't possible to dodge they can effortlessly rip a ship apart far faster then any large gun can for their size, but they generally have low muzzle velocity and can't help at long range making them part of a ships secondary batteries.
Medium range weapons: Medium range weapons serve as general purpose for most cases they have fair muzzle velocity and high damage potential if you have a ship meant to brawl with an enemy fleet, it probably has a majority of its weapons as mid range. These are generally large secondary or primary turrets built for damage potential over most other things, in general most ships are killed by these in galactic history battered down and broken under weight of fire from continual bombardment. While not being nearly as flashy as something like a large spinal gun or a massive main battery on a battleship, these generally cruiser grade weapons are what will deal the majority of damage.
Long range weapons: Long range weapons are the classic massive turrets you put on your battleships high muzzle velocity, very accurate high damage weapons with generally low fire rates smashing ships apart at long range with their oversized armaments. Long range weapons are for well long range combat of course being while very damaging and accurate at close ranges more of skirmishing tools at their proper range, to degrade an enemy fleet and destroy them when they close. These will generally be filled by large turrets however spinal mounted weapons, as well as anti ship missiles can fill the role of a long range option for navies with smaller more economical ships.
Modifications and purpose: In general these broad types of guns you can modify their meaning for instance a traditional type of weapon in scifi is a long range spinal gun, you can denote purpose and type of angling via these for instance point defense weapons in general their purpose is to defend against fighters and missiles and as such have much lower damage for their size but massively higher fire rate and turret turn speeds. Simple classifications for guns help out when designing ships and thinking of reasonable weapon counts and placement within a ship, while also keeping your space for engines and ammo generators and the like balancing out your ships for general combat as you should try to minimize the differences in classes of ships and minimize variance unless a need arises.
Movement and utility systems
Engines and maneuverability: Engines are by far the most important parts of ships its what keeps them from being simple stations and defensive platforms as well as being their largest defense and offense, as the range of enemy guns the chances for them to hit a ship and your ability to close are all determined by how fast you can move and maneuver.
To give a idea of how important engines are in a ship its much like how aircraft work ships are in a 3d space and so any way to save weight or improve engines are taken over practically anything else, as even the most armored plane will simply get ripped apart under any significant fire so to is with space ships a fast ship can close quickly with an enemy fleet negating their long range guns and rip them apart however speed and maneuverability aren't the same thing.
An example of how engines are structured comes with this transport craft while its a traditional naval vessel you will see quite the trend in its propulsion systems, their entirely built for a single direction as are most rocket engines ships need the ability to rotate in space and gimbal at high speed. You only ever need one direction of thrust, maneuvering engines are their to turn the ship so that it can point its main thrust towards where it wants to go, rather then massive backwards engines in a sense you would rather simply rotate the ship and speed up that way.
Ultimately most ships end up sacrificing massive amounts of firepower as well as armor in order to keep up in the high speed deep space combat that takes place on the forums, making it a massive limiting factor on the size of your ships and their resistance.
Vulnerable sections (sensors/radiators): Every ship needs its eyes and a water bottle to go with it thats where sensors come in and cooling systems such as radiators, i've grouped them together as vulnerable sections as many rules apply for both.
You can't armor a radar dish really nor can you properly armor optics or radiators for this reason in addition to sections devoted to fire control and other such systems, you will want to have many secondary detection areas and ways to get rid of heat so if you have a large mid section of your ship say explode you don't have to worry about the ship being completely disabled. Ideally any ship should be able to cool itself down several times over in case of explosion or radiator damage, as well as still detect enemies even if the ship is cut in half as such awareness is what gives you your ability to fight without it ships are rendered useless to put it bluntly