Ballast Control Valve

Like real-world vessels, ships and submarines in KSP must contend with keeping the craft level despite having a center of mass offset from the vessel's center of buoyancy. To do this, vessels use ballast control tanks that hold seawater (Intake Liquid in Sunk Works). The Ballast Control Valve lets you convert any fuel tank into a ballast tank and back again. It can be done in the VAB/SPH before the vessel launches, and in the field by an Engineer on EVA. Since the Ballast Control Valve is storable in a cargo container, you can retrofit a vessel in the field if needed.

A ballast tank operates in two modes: Ballast - Ballast mode is used to submerge and surface a vessel, but it cannot help the vessel remain level in the water. Trim - Trim mode is used to help a vessel remain level in the water, but it cannot help the vessel submerge or surface. There are several types of trim tanks to choose from including Forward, Aft, Port, Starboard, Forward-Port, Forward-Starboard, Aft-Port, and Aft-Starboard. By specifying one of these trim tank types, the Kommodore Sea 64 will know which tanks to fill and empty in order to try and keep the vessel level.

As noted above, SunkWorks uses Intake Liquid to fill and empty a ballast tank. To accomplish this, all you need to is ensure that the Ballast Control Valve is submerged when attempting to operate it. Each valve has manual controls to fill and empty the tank that it is attached to, and have multiple valves attached to the same tank, then they will all match the desired tank type coordinate to fill and empty the tank. Note that if you lock the tank's Intake Liquid resource, then the Ballast Control Valves attached to the tank will be unable to fill or empty the resource.

Kommodore Sea 64

While you can manually control your ship's Ballast Control Valves via their Part Action Window and mapped action group Actions, the Kommodore Sea 64 can greatly simplify things. It has numerous widgets for controlling when to trim for pitch and roll, how fast to fill the tanks, whether to be used for just trim or if it should also handle diving and surfacing, and others. Take the time to familiarize yourself with the controls and how they affect your vessel. Since each vessel is different, no one setting will handle all situations.

Trim Tips

1. Put the heavier parts towards the bottom of the vessel. This will help prevent the craft from capsizing.
2. Create ballast/trim tanks of equal sizes on all four sides of the vessel.
3. If the vessel pitches up and down, or rolls left and right, then it is probably filling and emptying the trim tanks too quickly. Reduce the fill rate and/or reduce the roll and pitch trigger. If that doesn't help, try locking out the trim tank's Intake Liquid resource.
4. Once you have leveled the vessel using auto-trim, try disabling auto-trim and using the aquatic RCS thrusters to adjust the craft when it is no longer level.

Above all, keep in mind that seagoing vessels will need careful design and may require many iterations to get just right.