By Korvettenkapitan Rico Jarschke and
Kapitanleutnant Roman Schwab, German Navy
Auf 100m gehen! (“Down to 100 meters”) the officer of the watch orders, taking a last survey of the surface picture through the observation periscope. The helmsman dials in the digits of the ordered depth on a keypad of the ship’s control station and the submarine begins its tilt and descends to 100 meters (328 feet).
An alle Stellen: Schleichfahrt! In an anti-submarine warfare (ASW) duel against a nuclear attack submarine, the CO orders silent running. The helmsman pushes a button to change the operating mode of the ship’s control station and puts his hands on the two joysticks. For the next two hours, he will steer the ordered course and depth manually.
These are two examples for maneuvering a U212A-class submarine with the Ship’s Control Station (SCS)—developed by Italy’s Fiat Avio—as part of the integrated Engineering Maneuvering and Control System (EMCS) developed by Siemens. Not too long ago, on the recently decommissioned U206A-class boats of the German Navy, maintaining course and depth required three helmsmen: two controlling the fore and aft depth planes and one manning the side rudder. Nowadays this job is done by just one man, supported by a very sophisticated computer grid.
When the original design of the U212A-class submarines was conceived, the Cold War
paradigm was still the informing scenario. The central mission at that time for West German submarines was to leave undetected from the submarine bases in Eckernförde and Kiel and block Warsaw Pact forces from exiting the Baltic Sea through the Northern Approaches along the Norwegian coast. To do this, the boats had to negotiate the very shallow and confined waterways of the Kadettrinne connecting the eastern and western Baltic and the Great Belt opening the Baltic to the Jutland Sea. The depth of the Kadettrinne, however, is only 75 feet. This not only limited the size and draft of submarines, it required them to operate there at periscope depth and required high maneuverability. The 20.8 square meter (224 square foot) rudder area of the tail X- and fin rudders of the U212As guarantees turning rates of more than 200 degrees per minute to maneuver in shallow waters and near harbors and offshore installations. Even more important, though, is precision: at times it might be important to go to 41 feet and not 42.5 feet. This is where the SCS comes in. Even while conducting quick turns at periscope depth, the SCS is able to keep the ship on depth. If there is a need to go deep quickly, a U212A is able to reach maximum operating depth within two minutes with all planes on full dive.
As in most navies, the helmsman is supervised by the diving officer of the watch, who is also the engineering control supervisor, a task usually assigned in the German Submarine Service to an experienced engineering CPO. However, due to the easy and intuitive steering system, the helmsman watch aboard a U212A-class submarine is manned by the boat’s paramedic, the radio operator, and the sailors of the electronics department. To be capable of operating the SCS under stress in all conditions and emergency modes, all helmsmen are trained and drilled at the German submarine training center’s depth steering simulator. To follow the maxim “train as you fight,” a real world SCS provides optimum training benefit to the trainees, while the movement of the three-axis motion simulator gives them the realistic feeling of driving a submarine even in heavy seas. A prominent feature of the SCS is its capability to change operating modes, thus providing the CO the ability to optimize the performance of the system for different tasks. The A-mode (automatic mode) reduces the strain on human resources, requiring less concentration from the helmsman on long transits. The helmsman simply enters the desired course, depth, and ship’s angle via the keypad. The computer system moves the control surfaces to reach the ordered parameters, then holds the depth within one foot and the course within half a degree. The variables are constantly monitored, and any divergences beyond the limits allowed by the operator are reported with an alert signal. Only the roughest seas or very dynamic operations at periscope depth reveal the limits of the computer-controlled maneuvering.
In A-mode, the SCS calculates offsets for the planes to adjust for trim. Based on these offsets, the
EMCS is able to put the boat back in trim automatically by pumping, flooding, and trimming. Additionally, the system calculates a safe operating envelope depending on the current speed, depth, and rate of turn and/or descent, and an alarm sounds if the ship departs from this envelope.
A U-32 crew member operates the Integrated Engineering Maneuvering
and Control System
For ASW tasks, the preferred operating mode is the E-mode (Ersatzbetrieb – manual steering via joysticks). In E-mode, the planes are under direct control of the helmsman; he decides when and how to move the planes. This reduces the frequency of movements of the planes and reduces transient noises, but depth control is less precise. E-mode is in a way the multi-purpose mode of the SCS. The helmsman steers the sub with two joysticks, left hand for the sail planes and right hand for the X-rudder. Thus, the right joystick has both a rudder and a stern plane function. The helmsman views a screen that gives a graphic impression of moving through the water, similar to an artificial horizon indicator in an airplane cockpit. All turning, ascending, and descending can be monitored and manipulated in an intuitive way. Effective variables in follow-up control are the angles of the rudder and the planes. When A-mode operates at its limits, especially in rough seas at PD, a seasoned helmsman has the advantage. He can let the boat move with the sea to some extent and is not obliged to hold a neutral ship’s angle, as the computer would. But these are the only circumstances in which the helmsman can outperform the SCS. In fact, the opposite is more often the case: if the helmsman finds himself in danger of losing stable control, he can switch back to automatic mode; the
SCS will stabilize the submarine immediately, even out of extreme rates of turning or descending, and put it on an even keel. Then, the helmsman can safely revert to E-mode.
The SCS is a computer aided steering system that is multi-redundant. Several computers are computing the same values but are physically decoupled from each other, even to the point of having independent power supplies. The different operating modes are further redundancies in and by themselves and if all systems fail, the crew retains the ability to operate the planes mechanically, directly on the levers controlling the hydraulic valves of the rudder engines.
The X-rudder itself consists of four independently driven blades, each with an angle range of ±35°. Each blade’s angle will have an effect on the course and balance of the submarine. With all four blades, a total angle of ±35° stern plane or rudder can be achieved. It is also possible to order a plane angle and rudder angle at the same time as long as the sum is less than 35°. The sail plane is integrated into the tower construction and has an angle of ±25°. Its placement has been chosen carefully such that it will not affect the boat’s trim.
Although the maximum angle of any of the X-rudder blades is limited to ±17.5° the boat’s maneuverability is still impressive, even if two blades fail. Thus, the maneuverability is highly redundant, not only through the number of the blades but also by the design of the hydraulic system. The sail plane drive and each X-rudder blade drive has a redundant hydraulic oil supply and an additional emergency oil supply. Emergency control stations are on standby in all sensitive situations such as diving stations, shallow water operations, and piloting.
In more than seven years of operations with the SCS both in the German and the Italian submarine services, the dive-by-wire system has proven all nay-sayers wrong: reliability and precision are high and its maneuverability is quite impressive. Particularly in light of the challenge of recruiting and retaining highly qualified personnel, the significance of reducing the crew size and relieving crew-members from performing boring and tedious—but critical—tasks should not be underestimated. The second batch of U212As will therefore see little change with respect to the steering control system apart from the change of manufacturer. The drive of the sail plane is now hull mounted so that the steering rod no longer penetrates the pressure hull.
From the German perspective, dive-by-wire is by now a proven design. For the future, two avenues of development are conceivable to reduce acoustic signature of control surfaces: hydraulic drives with variable pressure supply or an “all-electric-ship” concept with electric drives for planes and masts.
Cmdr. (jg) Rico Jarschke is Head of Basic Operational Training, 1st Submarine Squadron, Submarine Training Centre. Lt. Cmdr. Roman Schwab is Head of Systems Support Submarines, 1st Submarine Squadron, Systems Support Group