(see this blog post in French: http://www.abysscrew.com/devlog-1-deplacement-du-sous-marin/ )
We wanted the submarine to behave realistically, particularly in the way it moves through the abyss. That’s why we imagined a submarine with five engines: two at the rear to propel forward or backward and three at the front to steer and stabilize it. A good example for this system is the two-seater canoe: if both people paddle on the same side, the canoe turns in one direction, but when they paddle on both sides, the canoe advances in a straight line. Synchronizing the front and rear engines allows the submarine to move while steering. It also gives the pilot more possibilities for dynamic maneuvers.
One of the first movement panel
However, during playtests, many people were having trouble understanding this mechanic. Operating the submarine was made much more difficult by a user interface that was not intuitive enough. The handling was also complicated: few people managed to coordinate and head in the direction they wanted, and then maintain that heading. It became obvious that this system wasn’t adequate for the player.
Therefore, we changed the submarine handling by reducing engines to forward/aft only, and a rudder to change direction. The user interface was simplified and made closer to what can be seen in a real ship. The controls suddenly became more appreciated despite the inertia: indeed, in reality, a submarine launched at full speed doesn’t stop in an instant, and it takes a while to slow down and stop. It’s the same in Abyss Crew.
Nevertheless, complications emerged, in particular when getting stuck in a corner of the map and unable to get going, as the submarine can’t turn back on itself. It was necessary to set aside realism to facilitate the handling of the ship: a rotation on itself, even when not moving forward, has been implemented*
The corresponding panel
Today, the final version of the mechanics for the pilot has been put in place: with the W and S keys, the player can move the submarine forward and backward, with three levels of speeds, taking into account the effect of inertia. A and D are used to rotate the ship, even when stopped, to avoid obstacles and enemies.
Current -and final- panel
* An Abyss Crew fan reported that azimuth thrusters allow to move sideways, so it's not unrealistic :)