design Drass patent N° BO2015A000127
When comparing a standard ventilation system, based on surface suction compressor to the Drass SVS, the Drass SVS presents additional technical advantages as follows:
Drass can supply High Pressure air through a small hose (1/2”) included in the Strength Resistant Umbilical Cable, from surface to the Ventilation Capsule, where the air is reduced to Low Pressure. From the Ventilation Capsule, a sho rt hose having adequate diameter is connected to the DISSUB; the diameter of LP hose depends on the volume and crew of the connected DISSUB. A smaller diameter hose allows a significantly smaller umbilical winch, resulting in a SVS which can be easily air-deployable (ISO 20” container footprint).
The suction compressor directly vents the DISSUB exhaust air into water at depth, therefore Drass SVS does not require a large diameter suction hose to be connected to a surface vacuum unit from depth. The overall dimensions of the surface equipment and winches are thereby reduced.
The Ventilation Capsule is only a few meters away from the DISSUB. This makes it easier for the divers or for the Working ROV (Remotely Operated Vehicle) to connect the LP Supply and Suction Hoses even in conditions of strong currents. The short hose offers a considerably smaller resistance to the current compared to the hundreds of meters of hose tendered from an assisting vessel operating a conventional ventilation system.
Prolonged exposure to low temperature is one of the highest threats to the survival of a DISSUB crew. Thanks to the availability of local energy, and to the temperature monitoring provided by the Sensor Bar installed in the DISSUB, Drass SVS controls the temperature of the DISSUB by achieving the desired Supply Air Temperature on the local Ventilation Capsule.
DRASS SVS Air Distribution system is designed to carry out flushing with a redundant source of breathable, clean air. The flexible architecture of the system allows two additional services:
On Surface: thanks to dedicated outlets, the Supply Air is also available for the pressurization of the Diver Decompression Chamber and of the Submarine Rescue Decompression Chambers
At Depth: thanks to dedicated outlets, the Supply Air is also available to vent the submarine ballast tanks and increase the buoyancy of the DISSUB, when the rescue team brings the DISSUB to surface.
VENTILATION SYSTEM OPERATION
- The vessel detects and tracks the DISSUB emergency signal, emitted by the emergency buoy.
- Following such localization, the Support Vessel maintains a close position to the DISSUB.
- The vessel crane is connected to the Capsule Clump Weight and moves the Clump Weight on the main deck.
- The Clump Weight Wire is connected to the bottom side of the Ventilation Capsule.
- The vessel crane is connected to the Ventilation Capsule in order to place the Capsule on the deck.
- The Strength Resistant Umbilical Cable is connected to the Ventilation Capsule.
- Using the main crane, the Ventilation Capsule is deployed at sea level with the Clump Weight hanging below. The Ventilation Capsule is lowered by the main winch until it reaches the operational depth with the clump weight laying on the sea bed close to the Midget (the distance between the Midget and Capsule will be about 15 meters).
- The ROV extracts the suction and supply hoses from the dedicated pods installed in the capsule. These cables are connected to the air ventilation and signal ports on the external surface of the DISSUB. The system complies with NATO STANAG 1450.
- A dedicated Sensor Bar installed in the DISSUB (optional) is connected through compatible pins, installed in the same air suction connector. The Sensors Bar is equipped with CO2, O2, pressure, temperature, video, infrared video, microphone and loudspeaker. Thanks to the Sensors Bar the relevant information is transmitted to the surface and properly managed to optimize the rescue operation.
- As soon as the supply and suction hoses are connected and the DISSUB environmental condition are verified, it is possible to supply the breathable air from the surface, operating the ventilation system from the dedicated control panel.
- The Submarine is flushed while keeping the internal pressure at atmospheric values. The Suction Compressor contained in the Ventilation Capsule carries out the flushing, discharging the air flow underwater and analyzing the DISSUB atmosphere.
- The SVS has the scope to maintain adequate survival conditions while submarine rescue operations are in process. After rescue operations, the Suction and Supply hoses are disconnected. The Ventilation Capsule and the Clump Weight are pulled by the Main Winch up to the surface, and then recovered by the vessel crane.
This SVS is compatible with Drass Midget Submarines and its dimensions can be tailored to the requirement of any conventional submarines.
- The product structure breakdown of the SVS is the following:
SVS Flat Rack
- Ventilation Capsule, including One (1) Air Suction Compressor
- Capsule Clump Weight
- Connection Umbilical Cables
- Retractable Roller Arm
- Sensors Bar & Control Panel
- SVS Handling Module
- Main Winch
- Strength Resistant Umbilical Cable
- Hydraulic Power Pack
- SVS Container
- Air Induction Container 20’
- One (1) Air Supply Compressor (200 bar)
- One (1) Back Up Air Supply Compressor (200 bar)
- One (1) Air/O2 Storage
- One (1) Air / O2 Mixer (Option)
- One (1) Supply Air Control Panel
- Diesel Generator (Option)
- Diesel Generator Container 20’
- Diesel Generator
- Fuel Tank
Drass Submarine Ventilation System is designed to provide sufficient ventilation to a DISSUB even in the most challenging and distressed emergency situations.
The concept of DRASS SVS is based on the utilization of an underwater Ventilation Capsule, containing a suction compressor which is therefore positioned immediately adjacent to the DISSUB. Thanks to the minimal size and length of the suction line, the compressor can satisfy the requirement of air recirculation without any pressure build-up inside the DISSUB, thereby operating at atmospheric pressure. By maintaining the atmospheric pressure in the Submarine, the evacuation of the DISSUB is achieved with a simpler, safer and faster procedure at every depth.
Traditional ventilation systems, on the other hand, which operate at depths of up to 650msw require a progressive increase in pressurization from a surface pump. The pressurization process requires complex and long decompression procedures and imposes transfer under pressure to a hyperbaric chamber after the evacuation from the submarine. Excess of pressure in the submarine can also cause saturation issues in the crew, with serious consequences during rescue and transfer operations.
Keeping the DISSUB at lower pressure values, however, would mean providing an insufficient flow of air to the DISSUB. While this is not perceived in a standard submarine ventilation exercise, in real operations the provision of insufficient flow of air can have fatal consequences for the DISSUB personnel due to the degradation of O2 content and the quick build-up of CO2.
The performance of Drass SVS instead is independent of the depth of the DISSUB thereby ensuring that performance quality is not restricted by time and depth variables.