I am building a submarine what is the best thing to use for a ballast?

Answer 1

Modern submarines use a variety of methods for ballast control. There are several factors that need to be considered:

1. Overall water displacement surfaced and submerged
2. Combined estimated weight of supplies and personnel aboard
3. Fixed Ballast (weights, etc.)
4. Main Ballast
5. Trim Ballast

Your overall displacement estimate will give you the target for how much fixed ballast you'll need to add for an estimate to keep the boat at submerged depth at neutral buoyancy while surfaced (most of the boat below the waterline). Keep in mind that ballasting requirements are different for fresh and saltwater.

You have to know the estimate of weight of all personnel, equipment and supplies onboard as well, since that also counts as part of the fixed ballast load. Knowing that allows you to know how much Trim ballast (used for maintaining more precise depth control and neutral buoyancy) you'll need to add or remove to achieve neutral buoyancy after you open the Main Ballast vents and submerge.

Any ballast you use must be distributed evenly across the keel, or you risk being heavy forward, aft, port or starboard. This is why Trim Ballast tanks are used also - they allow for precision leveling of the boat after submergence.

Without knowing your fixed ballast weight and how much Trim Ballast to add or remove, you can easily sink to the bottom or not submerge at all, though sinking is the more likely scenario. It's easy to sink a submarine - the trick is to get it back to the surface. As long as the number of dives equals the number of surfaces, everything's cool. If not, you're in for a bad day at work.