Depth control device

Details Depth control device Depth control device

2000-02-22

2000-11-07

Morano, S. Joseph

Ships

Submersible device

Having attitude control

441 29, B63G 814, B63B 2220

Patent

active

061420921

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a depth control device, in particular for use with submersible bodies.
Certain submersible bodies, e.g. towed arrays, such as towed sonar arrays and seismic streamers, or sonar buoys, are required to maintain a predetermined depth. Other submersible bodies are deposited on the sea bed and must then be retrieved. Still others, such are autonomous underwater vehicles (AUV's) require an effective depth control mechanism as they move through the water. Conventionally, the towed arrays are towed behind a ship and are required to maintain neutral buoyancy at a particular depth. A sinker is applied to the end of the array nearest to the towing ship to position that end of the array correctly and the remainder of the array is made neutrally buoyant at the desired depth, either by adding and subtracting ballast from the array or pumping fluid, such as kerosene, into its housing until the correct level of buoyancy is reached. The disadvantage of these methods is that they are expensive in ship time and manpower and if the array is moved to an area where the salinity of the sea is different, the whole procedure must be repeated.
Another system which has been proposed is to attach moveable hydrofoils along the towed array and control the angle at which the hydrofoils are set, so that as the array is towed through the water its depth and stability can be maintained. U.S. Pat. No. 5,619,474 describes a system of this type. However, these hydrofoils create noise and can impair the performance of seismic sensors on a seismic streamer.
U.S. Pat. No. 3,909,774 suggests incorporating pressure sensors in sections of a seismic streamer towed by a ship to control inflow and outflow of a buoyancy control liquid held in a pipeline alongside the streamer and serving multiple sections. The problem with this system is that it is bulky and relies on a connection to a pump and supply on the ship for the additional fluid pipeline required, so it is unsuitable for small bodies or independent vessels, such as the AUV.
Retrieval of bodies, which do not have their own form of propulsion, from the sea bed is typically done by attaching an air bag and providing a tank of compressed air which inflates the air bag to give the body sufficient buoyancy to return to the surface. Another way is to ballast the body e.g. with lead shot, then to disengage the ballast, so that the natural buoyancy of the body raises it to the surface. Both of these methods are only suitable for single use and disposal of ballast is potentially damaging to the environment.
A device for deploying instrumentation has been proposed which is dependent on the external water pressure acting on a piston until the piston comes up against a spring and then the piston continues to compress the spring until, at a predetermined depth, a spike beneath the piston impales a gas canister. The gas released forces the piston back up and provides sufficient buoyancy to raise the device back to the surface of the water. The instrument is retrieved and the readings recorded during the device's passage can then be read. This system suffers from the similar problems to the ballast or air bag systems, that the devices must be set up for a specific depth in a particular area of water and can only be used for one depth setting without adjustment and replenishment of the gas canister. Use of this system in towed arrays would involve significant time and expense.
In accordance with a first aspect of the present invention, a depth control device for a submersible body, comprises depth monitoring means and depth control means; wherein the depth control means comprises a controller and a variable volume buoyant body; the buoyant body comprising a first chamber containing a first compressible fluid and second and third chambers in communicating relationship with one another containing a second fluid, less susceptible to compression than the first; whereby a piston at the entrance to the first chamber is displaced in response to movement of the second fluid between the second

REFERENCES:
patent: 3436776 (1969-04-01), Davis
patent: 4031581 (1977-06-01), Baugh
patent: 4266500 (1981-05-01), Jurca
patent: 5303552 (1994-04-01), Webb

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