Ballast Tank General Question

[RCSubNewb01]

Im trying to figure out how much water in Liters I need for my ballast tanks to achieve neutral buoyancy.

My RC submarine will have the following dimensions:

• Length: 1.5 meters
• Diameter: 0.25 meters
• Total Weight: 40Kg (made of Aluminium) with 1cm wall thickness
• Shape: Cylindrical body with a half sphere shape at the head.

I've attempted to calculate the volume of water that the RC submarine will displace like so:

• Radius: 0.25m / 2 = 0.125m
• Volume of the cylinder: π * (0.125m)² * 1.5m = 0.0736m³
• Volume of the half-sphere: (2/3) * π * (0.125m)³ = 0.0082m³
• Total Volume Displaced: 0.0736m³ + 0.0082m³ = 0.0818m³

and thus the Buoyant Force when fully submerged would be:
F^b = 0.0818m³ * 1000 kg/m³ * 9.8 m/s² = 801.64 N

It looks like I need a ballast tank that could contain around 42 KG (81.76 kg - 40 kg = 42.07 kg) of water to achieve neutral buoyancy. That seems like a lot when i compare with other RC subs videos on youtube.

Am I doing something wrong here?

[trout]

Wet or dry hull? What ballast system? What sub? you really need just enough to lift whatever superstructure needs to be out of the water on the surface or water line. One is trim sub to water line, then add water to your ballast tank to overcome the positive buoyancy. The other way is trim to neutral buoyancy and add air to lift to water line. So, calculate only the amount above the surface add 10 to 20 percent. If you know the sub you are building, David Merriman has the knowledge to give you an idea.

[redboat219]

My RC submarine will have the following dimensions:[LIST][*]Length: 1.5 meters[*]Diameter: 0.25 meters[*]Total Weight: 40Kg (made of Aluminium) with 1cm wall thickness[*]Shape: Cylindrical body with a half sphere shape at the head.

building an AUV or a torpedo?

[He Who Shall Not Be Named]

Wet or dry hull? What ballast system? What sub? you really need just enough to lift whatever superstructure needs to be out of the water on the surface or water line. One is trim sub to water line, then add water to your ballast tank to overcome the positive buoyancy. The other way is trim to neutral buoyancy and add air to lift to water line. So, calculate only the amount above the surface add 10 to 20 percent. If you know the sub you are building, David Merriman has the knowledge to give you an idea.

Here's a sure fire cheat to find the actual amount of water you'll need. The process assumes that your WTC is neutrally buoyant. David Copeland taught me this trick:

Put in your fixed ballast weight -- between .5-5 lbs. depending on the boats size -- and put in a hunk of foam (positioned so that none of it will project above the designed waterline) and float the thing. Keep playing with the amount of foam till the boat floats at the desired waterline. That hunk of foam represents the volume of water your ballast tank has to hold. A little geometry gets you that number; enlarge that number by 15% and you're golden.

[Subculture]

"Total Weight: 40Kg (made of Aluminium) with 1cm wall thickness"

Are you sending it to the Mariana Trench?