A Rigid Buoyancy Devise ?

[Eastwest]

I started to make a rigid buoyance devise some years ago as to carry heavy objects underwater with only a need to trim at the surface to nuetral and no change at any depth. The trick is understanding how to vent off and add air similar to a submarine ballast . The bouyance devise will be a propane tank but was not sure where to put the air and vent valves . Easy Does It Rumdumb

 

[evandroairton]

Dacor and Scubapro made rigid BC's at the 70's.
Maybe you should have a look how they worked, but on your design probably manually operated opv on top and inflator at bottom. (Drysuit ones), or a bc corrugated hose and inflator
But wouldn't a lift bag be a simpler solution?

 

[rongoodman]

Why not just use a lift bag?

 

[gmerick]

A rigid device as opposed to a lift bag, so the buoyancy characteristics don't change with depth.
Look for something like the housing of a DPV. Add weight as needed at the surface, seal the device, and dive. A DPV housing is designed to handle the crush pressure at it's rated operating depth.
I'd worry about a propane cylinder, as it is designed to contain internal pressure, not withstand external.

 

[tursiops]

I started to make a rigid buoyance devise some years ago as to carry heavy objects underwater with only a need to trim at the surface to nuetral and no change at any depth. The trick is understanding how to vent off and add air similar to a submarine ballast . The bouyance devise will be a propane tank but was not sure where to put the air and vent valves . Easy Does It Rumdumb

How heavy an object do you want to support with your propane tank, for how long, and at what depth? You won't get more than about 333 pounds buoyancy, and the steel will rust. I don't know what the crush depth of the propane cylinder is...

 

[lowwall]

I started to make a rigid buoyance devise some years ago as to carry heavy objects underwater with only a need to trim at the surface to nuetral and no change at any depth. The trick is understanding how to vent off and add air similar to a submarine ballast . The bouyance devise will be a propane tank but was not sure where to put the air and vent valves . Easy Does It Rumdumb

Wait until these guys give up and then pick up a unit from the liquidation sale.

Avelo

diveavelo.com

 

[Bob DBF]

I started to make a rigid buoyance devise some years ago as to carry heavy objects underwater with only a need to trim at the surface to nuetral and no change at any depth. The trick is understanding how to vent off and add air similar to a submarine ballast . The bouyance devise will be a propane tank but was nⁿot sure where to put the air and vent valves . Easy Does It Rumdumb

Submarines use free flooding ballast tanks, which have to kept in a certain trim (pitch and roll) in order to keep the air bubble in the tank, if the air bubble escapes it loses buoyancy and sinks. If you put a bladder in the tank to avoid that, might as well use a BC or lift bag, and avoid the negative buoyancy of the tank.

As far as taking known weights down with you, using ridged foam would work, it would not be variable, but one could use their BC or small lift bag to make up the difference.
Subsea Buoyancy Foam: R-3312

 

[tursiops]

How heavy an object do you want to support with your propane tank, for how long, and at what depth? You won't get more than about 333 pounds buoyancy, and the steel will rust. I don't know what the crush depth of the propane cylinder is...

TYPO: make that 33 pounds buoyancy, not 333 pounds!

 

[Eastwest]

Thank you Bob for the Subsea tip and will definitely use some on my diver tow craft . All of this is a learning curve for projects and necessary to understand .