Siemens, MaK Cooperate With CCG For Faster Icebreaker Response
The Louis S. St-Laurent is the Canadian Coast Guard's largest icebreaker. Commissioned in 1969, she has a displacement of 14,500 tons and is driven by three fixed-pitch propellers each with a power capacity of 7 MW.
The Louis's main function is to serve as an icebreaker and ship escort in both the Gulf of St- Lawrence and the Canadian Arctic. In this capacity, one of its most important operational features is propulsion system response time.
Response time is generally measured as the time for the propeller drive shafts to go from full ahead to full astern. This shaft reversal is often referred to as "crash reversal" for free running maneuvers and this time would be in the order of 40 - 80 seconds for most commercial vessels. The need to both operate at full power in close proximity to other vessels, and the accuracy needed for repetitive bow-ramming of ice ridges, generally require a response time in the order of 10 - 20 seconds. The original turbo/electric DC drives of the Louis were replaced by a five-engine diesel/AC-DC system with MaK engines and Siemens Electric controls — during mid-life modernization in 1992. The new configuration allowed for dynamic braking and reversal of the motors by continuous field control.
Following this refit, the ship reportedly demonstrated a remarkable improvement in open water and icebreaking performance on the first Arctic mission. Analysis of ice trials data collected on this trip, however, revealed the propulsion system had untapped capability, as well as several interface problems between the new drives and the original telegraph consoles. The combined effect of these conditions resulted in shaft reversal times longer than the potential performance of the system.
The Cooperative Solution The CGC turned to Siemens Electric Ltd. of Montreal to help develop an innovative and cost-effective solution to the problem. With this project, the CGC also put in place its new mandate of Downward Delegation by giving the vessel's management team the entire responsibility for the upgrade. Every aspect of the project including specification development, contractor liaison, materials procurement, systems training, onboard installation and commissioning, and financial management would be coordinated by the Louis's own engineering crew.
Initial discussions were held between theLouis, Siemens, and MaK in May of 1994. A review of the propulsion response time curves showed that the existing control strategy did not initiate motor field reversal until the armature current had climbed to approximately 60 percent. This approach was originally adopted to improve fuel efficiency, but resulted in a nine-second lag from telegraph command until reverse power was exercised upon the propeller shafts. Other "delays" were identified in the time to unload the diesel engines and response time of the bridge telegraph consoles.
A plan was developed to make changes to three areas: telegraphs, engine control methodology, and motor control algorithms. The project was approved in November of 1994 and the Louis engineering crew immediately began work to minimize the downtime required to make the actual propulsion control change-over. This was considered a key element of the project, as the ship was about to enter its busiest operational season in the Gulf of St- Lawrence.
The Siemens work focused on changes to the electrical control software by which the armature current would be increased immediately following the telegraph command, and the motor field reversal would be achieved earlier. In this fashion, reverse power could be brought to bear on the propeller shafts much earlier while still respecting the engine unloading limits.
Through careful planning the bulk of the upgrade was able to be completed while the vessel remained in operational status. Approximately; one week of downtime was required to install the new bridge telegraph consoles and "tune" the new control software. The resultant propulsion response time curve showed that shaft reversal time had been reduced to approximately 21 seconds, a reduction of close to 65 percent. Further improvements are anticipated by additional electrical control software changes which would sense the operating condition of the engines, and use the power absorbing capability of each engine and the heat-dissipative tolerance of the motors to more quickly stop the propeller shafts. Response times of 10 seconds or less may be achievable using this approach.
Overall Project Benefits The improvement in shaft reversal response time for icebreakers has other benefits in addition to the operational performance criteria listed earlier. Perhaps the most significant is the anticipated reduction in engine maintenance as a direct result of reduced engine cycling. Eliminating the need to have more engines running for maneuvering flexibility in ice conditions, and altering the engine unloading/ loading strategy used to control motor amperage current, will positive affect engine maintenance.
The project was completed well within budget and in a four-month total time frame. By taking the vessel management team approach to this project, the CCG realized significant savings not only in external contractor costs but in the ship's operational availability — since downtime was limited to seven days, compared to an estimated three weeks for a typical shore-based managed project of this magnitude. Further benefits will be derived, since the vessel now has an engineering crew an extensive understanding of the new system, and a stronger relationship has been developed with the external suppliers.
It is expected that this will translate into reduced maintenance costs in the future.
Overall, the CCG was pleased with one of its first efforts to make its operation more cost-effective and commercially driven by delegating more "hands-on" responsibility to its front line vessels. The management and crew of the Louis S. St- Laurent have demonstrated that the benefits of vessel management and project ownership far exceed those derived from more traditional shorebased management projects.
