Hi there, I'm during develop of sandbox simulation game Battle for steam and iron, it allow to build any water, sub-water, air and even land combat vehicles. Constructions are made from fixed size blocks, like engines, propellers, many kinds od weapons, floaters, storages for fuel, ammo, cargo and places for vital part of any ships a crew.
Good ship build must consider ship shape for receive best speed and maneuverability, gun placement to get best fire cover, place enough floater or balloons to alow ship fo float or/(and) fly, have space for supplies for engines, weapons and crew needs. Game have advance ballistic and armor penetration, damages mechanic so beside good construction ship be proper use, so player must deal aiming, fire, flood, repair control. Armor angling technique known form WoT can be also used.
Ships simulation is main aspect of game but I want add another strategic layer, this mode simulate living world from perspective of map, with cities, fraction and NPC fleet moving between them. In case of battle ships from engaged sides will be spawned as blocks construction on simulation map.Ships this mode are going to consume fuel, will have limited view range. Player can do a missions for fraction, be a pirate, trade between them or do whatever they want, gamplay similar to Pirates! or Mount an blade strategy mode.
Another gameplay mode will be combat scenarios with goals and spawn set of enemies (or allies) construction. Goals like destroy, sunk, bomb something, escort/attack convoy, multi ships battle, transport goods and survive, maybe race or goods deliver with minimized fuel use. Also will multiplayer in mode 1 vs 1, scenario co op, creative sandbox.