Small, Unmanned Buoyancy Control Device

[bd103dall]

I need a small buoyancy control device which can fit into a 4 inch diameter cylinder. Once dropping the cylinder into the ocean, it needs to achieve nuetral buoyancy at a depth between 50-250 feet, stay there for some period of time (anything over a few minutes would work) and then come back to the top. Any ideas on how I could either create such a device, or purchase an already commercially available product that would work?

 

[zeusfaber]

In the absence of any more constraints, a quick and dirty way of achieving this would be to tie the cylinder to a buoy using a piece of string of adjustable length, and sink it with a ballast weight attached with a salt block.

A.

 

[GregLamberson]

Nothing easy or simple comes to mind. There are self inflating bladders, you could use 2 ea of these (you would need to determine nuetral buoyancy). You could fix a depth gauge to one that would activate the "nuetral" self inflation bladder at a certain depth. Have a timer set to the other to activate the 2nd bladder that would then raise it to the top????????????????

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[IRstuff]

The simplest solution might be to use the string idea to begin with, and include a CO2 charge and an attached balloon. When you're ready, or a timer counts off, release the CO2 into the balloon.

TTFN

FAQ731-376

 

[GregLocock]

Depth charges used a soluble aspirin or boiled sweet as a time-of-immersion detector.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[zeusfaber]

For examples of how people use agricultural (ie cheap) engineering to make things lurk in mid-water for a while before doing something different, try Googling a term like 'sonobuoy sink'.

Sonobuoys are meant to sink at the end of their lives rather than resurface, but the ideas are all there to adapt.

(as you probably already know, trying to hold set depth using any sort of close-coupled gas-filled buoyancy bag is very difficult. Any increase of depth compresses the gas, making the device less buoyant and tending to increase the perturbation - such static instability means you need a dynamic control system which is almost certainly more complex and expensive than you really want. That's why submarines usually rely on hydrodynamic surfaces to control their depth).

A.

 

[unclesyd]

They use to have pop-up marker buoys used for lobster traps but I understand that they are not allowed anymore.

There are other pop-up buoys using different approaches used for marine research. The problem with any of these type buoys is sizing the anchor line based on the free buoyancy of the device.

As I recall these research buoys were made by "Benthos".

 

[dsparks]

bd103dall were you able to get what you wanted for the buoyancy control device? I used to work in the sonobuoy industry and have used and designed several types of BC devices so if you need additional information contact me at dsparks@sealandaire.com

 

[zeusfaber]

I'd forgotten this thread.

At a trade show last week, I saw someone giving out keyrings. The twist was, each fob concealed an open ended polythene float and a mixture of acid and carbonate powders. If your keys fall in the water, the mixture fills the bag, bursts the fob open and floats everything safely to the surface.

Sweet idea - now all they need to do is find a way of stopping it going off in your pocket the first time you get gophered.

A.