Neutral buoyancy of a submarine

Does anybody know how I can calculate what Force is needed for a submarine to get a Neutral buoyancy???

 

Well bouyancy is an upward force that you feel when your in a fluid, not necessarliy a liquid, though probably water for a submarine. This force is equal to the gravitational force on the water that the submarine displaces. Neutral buoyancy is when this is equal to the gravitational force on the body itself, i.e. it has no desire to move up or down in the liquid. So id start by calculating how much water your submarine displaces and thus the upward force, then workout how much your sub needs to weight to counteract equal this. In real life this is done by filling tanks with water.

 

In the simplest terms, the sub simply has to weigh the same as the water it displaces.

Figure out the volume the sub takes up, figure out the weight of this volume in water (might as well make a distinction between saltwater and freshwater), figure out how much the sub weighs with whatever load is aboard, how much ballast will be needed to bring it to equilibrium...

 

Thanks.
But can you also use this equation
Fa=g*density of seawater*V

How do you calculate the weight of the water that is displaced by the submarine

 

Well, you need to know it's volume.

You can get an approximation by treating it as a simple cylinder with 2 conical ends, then making an allowance for the conning tower, rudders, prop, and other appendages.

If you are talking about a scale model, the best way would be to submerge it in a tank, and directly measure the volume of water displaced by means of markings on the tank wall.

Once you know the volume displaced, multiply by the appropriate density for fresh or salt water.