/diy/ - Do It Yourself

>>1182241
To continue, if you do plan on going the full 64m down without having to dump weight to get up again, a 300psi tank would need to have more than 1/3 the volume of the ballasts, which is pretty big, and that's only one cycle. Of course you're not going to be pumping quite the whole ballast system full to ascend, it should require less than that.

Now pic related is important. Depth "d" is the maximum depth you can go before your ballast tanks even when full of air do not have enough buoyancy to get you going upwards. Since when you go deeper the air in your ballast tanks increases in pressure, it becomes more dense, until the net density of your submarine is greater than water. It's not like you won't have detachable weights, but it's still a bad idea to get to this point. If your ballast tanks are too small then the two lines "full" and "empty" will be too close together and limit the maximum depth. You can translate them up and down by changing (increasing) the weight of your sea craft, but you can only move them further apart by increasing tank volume. By the looks of things you should be fine. I'm currently working on the maths to figure out how big of a ballast tank you need, but it might take a bit.

Theoretically the maximum depth you can go with ambient-pressure air like this is 8.3km below the surface, which is 5/6 of the way down the Mariana Trench.

>>1182243
Propane might be a good idea by ease of use, but it is twice as dense as air.