Sea fortresses or just fortresses are HUGE gun platforms with guns aiming in all directions, as well as armor and other elements. They are slow and larger ones can't turn, but make up for it with versitality in gun placement.
Usually depending on the ship's size, they have weapons that are as large as possible and fit those onto their hulls, but the massive ones, just place a lot of 46cm guns.
In in addition to heavy cannons, they also make use of aircraft, to add even more firepower. If one uses alot of guns above deck, or uses a smaller ship, they might add runways below the deck, just note that if the ship is crippled, the runways will sink below sea level, making it impossible for aircraft to land, or land effectively.
Depending on the desired size, one can use differing blocks. These are the recommended or likely used blocks
hull, deck, ballast, lightweight armor, rudder propeller, small-angled boiler, 47mm guns -30.5 cm guns
Hull, large hull, lightweight armor, large lightweight armor, small-angled boiler, 47mm guns- 40cm guns, several propellers, any rudder
Large hull, large armor, hull, lightweight armor, armor, med-angled boiler, any weapon, several propellers, large rudder
Large hull, large armor, 6x6x2 armor, lightweight armor, armor, any boiler, any weapon (thought large amounts of it), many propellers, NO RUDDER (glitch prevents turning in huge enough ships)
The future is questionable for the fortress. Ships are being able to move faster, which can be a nuisance to fortresses. In addition, the battleship is slowly being phased out, with the addition of compact but powerful guns, like the mk45, some fortresses will be superior, even if they are the tiny ones. The larger ones might not survive such a fight, being huge and poorly mobile, but those who are outfitted, will still stand. Some ships can be fitted to work in this new age, but those that can't compete, will be scrapped.