Underwater Jet propulsion?

[mxracer19]

Recently, there was a thread about underwater sleds.

but what if you could build an underwater jet engine? Jet engines work by superheating gasses, and using the expanding gasses in conjunction with a nozzle to produce thrust. By with a scuba tank, you already have compressed gasses.

So what if you could use a tank of air with a sort of nozzle for short dstances at speed? Just crack the valve...isnt this how squids move except with water?

 

[derwoodwithasherwood]

If that doesn't work, try filling it with baking soda and call it an underwater solid fuel rocket. :rofl:

 

[DA Aquamaster]

The theory is good, but the scale is all wrong. Jet engines consume truly huge quantities of air and an AL 80, or even several AL80's would not provide a whole lot of range as it is just not that efficient blowing out a nozzle at the low speeds involved.

To be more effective you'd have to have a rocket using air, nitrox or O2 as an oxidizer and burning some other type of fuel. Hydrogen would be preferable as the by products would essentially be water and would not overly alarm the environmentalists (more than they would already be alarmed at the idea of rocketing around the reef.)

Using the compressed air to run a propeller would be more efficient and has I think been tried before. Using CO2 would be an even better idea as it would allow much more gas in an AL80 sized tank.

Hmmm...there could be a workable idea there. CO2 powered motors used to be pretty popular for small freeflight aircraft models. They are simple and lightweight and no combustion would be involved other than lightly carbonating an already heavily calcium carbonated reef, there would be no ill environmental effects. A very simple recoil starter would be a safer alternative to spinning the blades maually to get the prop and motor moving and the motor would then keep running until it ran out of CO2 or until you shut off the CO2 to the engine.

All you'd need is a CO2 tank, a simple regulator, a control/throttle valve, a recoil starter and an massively upscaled single cylinder model aircraft CO2 motor driving a gear box and propeller and a housing to hold it all in a streamlined scooter shaped package. You'd probably need a check valve in the exhaust to prevent sea water from backing up into the engine when it was not in operation but there would be much less that would need to be sealed and waterproofed compared to an electric scooter and it would probably be more reliable than an electric scooter. Plus you could "stage" other CO2 tanks and change them on long dives, unlike batteries in electric scooters.

Anybody know a patent attorney and someone with some money to invest?

 

[murphdivers286]

sounds interesting. This is how diving has evolved threw the years.

 

[derwoodwithasherwood]

using air, nitrox or O2 as an oxidizer and burning some other type of fuel. Hydrogen would be preferable as the by products would essentially be water and would not overly alarm the environmentalists

My brother has a 2-stroke gasoline piston engine powered u/w scooter that uses compressed air from a Scuba regulator. (It also has a snorkel for surface use) It runs forever on a couple of cupfulls of gas and will tow several divers around with ease. I never thought of the implications of the exhaust contaminants though. I wonder how feasible it would be to run something like that on an environmentally friendly fuel? Or perhaps a fitch catalyst and biodegradeable oil?

 

[willydiver]

My brother has a 2-stroke gasoline piston engine powered u/w scooter that uses compressed air from a Scuba regulator. (It also has a snorkel for surface use) It runs forever on a couple of cupfulls of gas and will tow several divers around with ease. I never thought of the implications of the exhaust contaminants though. I wonder how feasible it would be to run something like that on an environmentally friendly fuel? Or perhaps a fitch catalyst and biodegradeable oil?

Got to see a picture of that one. Never heard of it before. Any links to a website about it???

WD

 

[derwoodwithasherwood]

Actually, it was the ultimate DIY project: http://www.aquascooterusa.com/aquascooter_story.htm

Interestingly, I don't see the scuba reg adapter listed on the site. I thought he said it was an optional accessory, but maybe it was 3rd party or something he made himself. I never tried that part, just the snorkle. There's a limit to how deep you can go with it anyway -- below a certain depth the exhaust backpressure is too great and the engine dies. I used it a few times for shore dives -- motored out to the site, hung a dive flag from the snorkle, dropped a small anchor from a reel and used it as a dive float. If you tie a rope to the handle, you can tow a couple of divers hanging on to the rope. Cute toy but not cute enough that I rushed out and bought my own.

 

[DA Aquamaster]

There's a limit to how deep you can go with it anyway -- below a certain depth the exhaust backpressure is too great and the engine dies.

Good point on the backpressure issue. The same increase in backpressure would occur with a CO2 motor, so the regulator would also have to compensate for ambient pressure to maintain the pressure differential. Which would also mean the range would decrease with depth. That would potentially give the advantage to an electric scooter depending on how the tank capacity compares to battery capacity for a similar sized scooter.

 

[willydiver]

Man that's pretty neat. Thanks for posting that bit of history.

WD

 

[hdtran]

you could always resurrect the steam torpedo engine--compressed air (or oxygen) & alcohol burn, mix w/ water to make steam, & run a turbine. 5000 or 6000 yards at 30+ knots...