Greetings.

How would you build a lightly ballasted hollow vented ball, cylinder, any shaped contraption... that when tossed to a -say pool- it begins filling with the water and the air bubbles escaping at somewhere, somehow provide horizontal propulsion while sinking ?

Any brilliant occurrence comes to your mind ? 🤔

4 hours ago, Externet said:

Greetings.

How would you build a lightly ballasted hollow vented ball, cylinder, any shaped contraption... that when tossed to a -say pool- it begins filling with the water and the air bubbles escaping at somewhere, somehow provide horizontal propulsion while sinking ?

Any brilliant occurrence comes to your mind ? 🤔

Using exhaust air as the driving medium is a tough call as it carries so little momentum.

First notion would be a conventional sealed tanker hull with forward water intakes funnelled into turbines which drive fan-assisted exhaust air ducts discharging aft.

Not great since fans are fairly low efficiency devices, and much of the limited input energy would be lost as heat. Never going to match a pair of high efficiency propellers, or possibly even better, pumped water jets again discharging aft. But these deviate from the letter of the OP.

Edited 15 hours ago15 hr by sethoflagos
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As sethoflagos says, there’s not much to be gained here. you’d need a check valve, or have the inlet primed, to make sure the air escaped the right way, and since the air is going to gather near the exit, it’s liable to point nose down and any propulsion would make it just sink slightly faster

Any engineering to mitigate that probably isn’t worth the effort.