Future Submarine Steering
Submarines are highly capable weapon systems. They operate in a three dimensional space with constantly changing environmental conditions as temperatures, density layers, drift and weather, depth - to name only a few. To maneuver in this challenging environment in the required precisions is a challenge on its own.
To give an example: A cylinder of 4,000 tons with a speed of a few knots has to be kept in a depth range of a few centimeters to guarantee that the raised periscope stays above the waves even at high sea states. Compared to this flying a jet seems easy.
The classical submarine steering system
The classical steering system onboard of a submarine comprises of a one man or two man console operated by means of joysticks, stickwheels, levers or a combination of both. For all rudder configuration (e.g. X-Rudder, + - Rudder, …) it offers different modes of operation as manual operation, automatic mode and emergency mode.
In manual mode the hydroplanes forward and aft and the rudders are steered by the helmsman. Typically the hydroplanes/rudders (forward and aft) are linked to each other so that the steering system takes care of acting on the rudders depending on actual speed and the demanded depth change given by the helmsman. In certain situations it is advantageous to decouple the hydroplanes/rudders forward and aft and operate them separately.
In automatic mode a 3D Autopilot takes over and keeps the set depth and course. In a “mixed mode” the helmsman might steer and control course/heading in manual while the Autopilot keeps the set depth or vice versa. This was the task of legacy depth and course pilots as well whereas modern systems perform complex depth changes, preprogrammed maneuvers and dynamic predictions as well. All this in a preciseness and smoothness comparable to a well-trained helmsman.
The emergency mode takes care of situations where the submarine has a loss of mains and has to operate as save as possible.
Today the steering console of a conventional submarine is interfaced with the sensors and systems directly necessary to perform the task of steering the submarine, e.g. the depth sensors, essential navigation data, the actuators for the hydraulic rudder engines including the feedback from the rudder position transmitters and the engine control. This principle limits the submarine design and operation to a high degree as it does not take advantage of already available technologies in terms of data distribution onboard like on commercial vessels and even surface combat ships.
In times of rising integration level enabled by technical innovation:
- Increased interface bandwidth (serial line 38400 kb to Gigabit Ethernet and beyond)
- Interface connectivity (serial point-to-point to Ethernet networks allowing arbitrary interconnection topologies)
- Processor power (assembler programmed controllers with a few MHz to multi-core CPUs with several GHz)
- Storage and memory size (from a few MB hard disks and a few KB of RAM to storage arrays and several GB of RAM)
- Reduced power consumption as more and more power saving designs were introduced as the mobile device market heavily relied on their availability
one can step back and rethink system design. Networks replace point-to-point connections, general purpose CPU boards replace specifically designed processor cards, and modularized SW architectures using shared data models in common network infrastructure replace monolithic SW designs.
Utilizing a ship-wide data network for submarine steering
The transition from point-to-point communication to a ship-wide data network – and thus a fusion of all available data (automation, navigation and combat management) – can strongly contribute to a broader situational awareness. Utilizing a ship-wide data network for submarine steering should evolve and give freedom to the designers and operators up to non-permanently manned steering consoles arranged wherever feasible.
In addition, utilizing a ship-wide data network can also allow a higher degree of freedom where to arrange functions like steering as all necessary data is available everywhere. As steering relevant data - improved in integrity, reliability and accuracy by certain data fusion algorithms - is already available through the network, a dedicated steering console mainly consists of the HMI, the status displays and the computer systems to host these functions. Except the stickwheel or joysticks each modern multifunctional console aboard consists of the same components and would therefore be able to be used for submarine steering.
Further, as route planning is common on all commercial vessels using integrated bridge systems, it is only logical to transfer this feature to a 3D route planning onboard of a submarine. Defined waypoints are handed over to the steering system’s autopilot and supported by safety features as dynamic safety envelopes. Joining the common infrastructure certain features like a highly-accurate 3D-Autopilot and 3D-waypoint-planning can reduce helmsman activities to a great extent.
The effects are obvious. The space for the dedicated steering console would be obsolete. And, even more important, the steering station (which needs not to be one dedicated console anymore) does not need to be manned at all time. A partially unmanned operation becomes possible during low profile operation such as transit. The steering function itself of course has to be monitored; but this can be done by another active operator such as the navigator. The tasks in submarine steering during low profile operation therefore may shift from feeding the steering system with course or depth information to a rather supervising function.
And the steering system is only one system that would benefit of such paradigm change. Including steering in a network would also open the door for advanced mission planning and performance. Summarizing all changes the submarine could get smaller, more capable and use the available energy more efficient (hence reducing hotel load) with the benefit of longer submerged endurance and lower signatures.
Advanced safety and alarm management for highly automated operation
A basic requirement for having multiple steering workstations onboard (such as the steering console and the navigation workstation or other multifunctional consoles) is a common HMI. It is essential there is no “break” between the different steering workstations and its operation concepts, especially if an operator switches due to a changed mission profile from system A to system B.
The acceptance of increasing the automation of submarine steering will also depend on increasing the safety and alarm management. This implies an advanced control (e.g. track control) which also considers dysfunction and drift of sensors over time while being submerged and, for example, not connected to GPS. In other words, an advanced control requires a highly reliable integrity monitoring. Furthermore, the respective alarm management shall take into account all relevant information being part of this process.
From a functional point of view simulation and training capabilities must not be missed. Future steering will support the helmsman with a “virtual submarine” presentation – performing training sessions without interfering the real submarine.
In addition, the safety and alarm management can be supported by specific safety features (e.g. safety envelope, bottom navigation, forward looking sonar), which among others prevents critical depth to the autopilot and/or helmsman. Another aspect is a reaching a higher level of redundancy by having more than one dedicated steering console onboard (e.g. steer the boat from the navigation workstation).
Further, the aviation industry uses fly-by-wire technologies including additional features like “force feedback” joysticks or stickwheels, which provide vibration warnings in extreme maneuvers when reaching defined limits. This might be a future scenario for research projects regarding safety improvements in submarine steering consoles.
Implications on efficiency and life cycle cost
It is well known that decreasing budgets, which also have to be share among a larger spectrum of assets, are increasingly challenging the Navies. Besides operational advantages for the crew and manning concepts, the proposed concept leads to additional benefits in efficiency and maintaining the operational capabilities of the system.
The before-mentioned lower manning concept during low profile missions can have a large impact on the life cycle costs while considering a submarine operation for decades. This fact alone should suffice to investigate this concept even further.
Another aspect is the improvement of the efficiency of the submarine in terms of fuel consumption. This is even becoming more and more important. In this regard, it is possible to have an advanced route and mission planning considering way more environmental data that is considered in the planning process right now. The commercial shipping is already trimmed to efficient operation and should be the archetype for the submarine world. As soon as the advanced route and mission planning is done, the next lever of fuel saving can result from further optimizing the operation for the rudder system (e.g. rudder movements) by an automatism (like an autopilot). This ‘efficiency autopilot’ will determine the most economical way from point A to point B (also the fastest way would be possible, however as a trade off with the fuel efficiency). This could be an improvement for periods of lower demanding phases and operations.
It is also obvious that such paradigm change would not only create benefits within the steering system but also contribute to advanced mission planning and performance. Finally, implementing latest generation technology also enable a simplified and more efficient updating and upgrading process over lifetime, providing essential flexibility to adapt to the faster and faster changing security situations and missions.