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SAGA submarine

The following article is a summary of the statement of Mr. J. Mollard and D. Sauzade at the symposium ISM 90, the 3, 4 and 5 December 1990 in Toulon.
To read the full text of this intervention, click on this link.
It is difficult today to know what became SAGA, if it was used, if it answered to the expectations of its designers.

Developed in France by IFREMER and COMEX, SAGA is the first prototype of a new generation of industrial submarines capable of carrying out underwater operations using divers or robots at close proximity to the work site without surface assistance.

SAGA (28 meters long, 550 tons submerged displacement, 6 crew members) has a hyperbaric compartment for 4 to 6 divers. Several important innovations, in particular with regards to energy, give SAGA an exceptional autonomy, essential for performing deep underwater operations.

The submarine was launched in October 1987 and has just completed a three-year qualification programme. Since May 1990 SAGA holds the world record of the deepest (-317m) diver lock-out operation from a submarine.

Main parameters:

Overall length 28,06 m
Overall width 7,40 m
Height except antennas 8,50 m
Displacement in surface 303 T
Height under the water 3,65 m
Displacement in diving 545 T
Maximum immersion 600 m
Immersion for the human diving 450 m
Power generators.
On the surface: 1 diesel engine HISPANO-SUIZA 175 kW
In immersion: 2 Stirling engines 2 x 75 kW

Storage of gas and energy:

Fuel 6200 1
Cryogenic storage of oxygen 6500 kg
Air, gas of diving and oxygen 5600 Nm3
Principal battery 700 kWh
Total energy stored on board (electrical and chemical) 10500 kWh

SAGA is equipped by two Stirling engines which provide during diving the power necessary for the propulsion and the power supply. They also produce the heat used for the heating of the hyperbaric compartment as well as the heat to protect the divers against the cold during their work.
The development, industrialization and commercialization of the Stirling engine for marine propulsion have been undertaken since the 1970's in Sweden by the United Stirling now integrated into the shipyard Kockums in Malmo.


Gas of work: Helium (130 bars).
Pressure of combustion 22 bars
Speed 2400 rpm
Fuel consumption 260 g/kWh
Oxygen consumption 980 g/kWh
Maximum power 75 kWh
Recoverable heat from the combustion gases 18 kW.
The main problems of development were:
- the mechanical resistance of materials subjected to strong temperature variations.
- the sealing on parts moving with respect to helium with strong pressure(130 bars).
- the control of the complex flows of the fluids at very high temperature (200 to 2000 ° K) in the combustion chamber.
- the realization of exchangers (regenerators) with very large surface of exchange and low thermal inertia

The waste gases, being at a pressure of 22 bars, are evacuated directly for immersions lower than 200 meters. Beyond and until the maximum immersion of the SAGA (600 meters), it is necessary to pressurize these gases and the condensates, which required the development of a specific compressor produced by GIE SAGA.

SAGA is equipped with two cryogenic tanks located outside. Gaseous oxygen and its pressurization are obtained by vaporization in exchangers heated by ambient sea water.

The gravimetric density of the module of energy of the submarine, including fuel, oxygen, storages and the two Stirling engines, is approximately of 0,25 electric kilowatt-hour per kilogramme without taking account of the heat recovered for the divers. This performance is much higher than those electrochemical sources and comparable to those of fuel cells still under development.

Assistance by two computers.

The System of Supervision:

A computer manages approximately 300 sensors of various nature.
The system of supervision has various functions.
. Presentation of the operating conditions of the installations (propulsion, storage of gas,...).
. Navigation assistance in managing the various apparatus on board.
. Helps with safety by the management of alarms, the follow-up of the parameters of operation and the device “man dead”.

The system of regulation of energy:

It manages in an active way the unit of the installations on board concerning energy and the propulsion: diesel engines, Stirling engines, electric generators, propulsion engines.
The tests have shown that these systems reduce considerably the task of piloting since the submarine can be operated by one person.

SAGA, with Stirling engines equipped with a compressor of exhaust, was tested to a depth of 600 meters.
This configuration made it possible to use the submarine in its complete operational area. It was thus possible to achieve a complete saturation at a depth of 300 meters for four divers and to bring the world record of intervention by divers starting from a submarine at a depth of 317 meters, May 6, 1990 off Cape Bénat (Var)


SAGA is now available to carry out a large variety of underwater work until depths of 600 metres, in a very competitive way compared to the conventional means.

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This site was created and is maintained by Pierre Gras. Thank you with all the people who contributed their shares: articles, photographs, videos, worksheets. The author is opened with any suggestion allowing to improve this site for happiness of everybody. Finally, a big thank you to Robert Stirling !

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