Healy really cuts it

Although the US Coast Guard cutter Healy was placed “In Commission, Active” on August 21, 2000, details of its capabilities were not fully appreciated outside the USA until a recent visit to Dover. The icebreaker was on its way north to complete its first scientific mission to explore the Arctic?s Gakkel Ridge. The $350 million vessel, built at Litton Avondale Industries in New Orleans and delivered to the USCG in November 1999, was paid for out of US Navy?s budget funds since the cost of the ship would have taken up a giant portion of the Coast Guard?s funds allocated for newbuildings. At first glance the 16,500t displacement vessel looks very much like any other icebreaker. It has the traditional cut-away forefoot, a solid looking 130m long by 25.2m wide hull and a large funnel indicative of the powerful propulsion power plant installed. However, the vessel has a bigger than average accommodation block which belies its main function, that of a high latitude oceanographic research vessel. Living quarters are provided for up to 50 scientists in addition to six labs, two climate control chambers and a library/conference room, all of which make for an enlarged superstructure. Another visible difference is the A-frame located on the after deck which is used in conjunction with the two double drum trawl/core oceanographic winches. Healy is the first full diesel electric US Coast Guard polar type icebreaker to be fitted with AC drives incorporating a cycloconvertor-fed synchronous motor propulsion system. The vessel is also the only unit in the icebreaking fleet to use the state-of-the-art fully automated system for the control of the ship and the machinery plant. Electric propulsion Alstom designed the entire package of power system, propulsion drives and onboard control/diagnostics systems at a cost of $30 million. A high degree of operational redundancy features has been incorporated in the power and propulsion systems starting with four Sulzer 12Z AU40S diesel generators supplying electric power via a 6,600V AC switchboard common bus distribution system. The switchboard is split into two sections housed in separate compartments minimising the risk of fire and flood damage. This system provides several distinct advantages; eliminating the need for separate ship service generators, providing redundancy in the power generating plant, and offering the flexibility to operate only enough generators to supply the required load while permitting maintenance to be performed on the other units. Two fully reversing, variable speed, AC synchronous motors fed from the common bus through an AC/AC cycloconverter system provide propulsion power for the two fixed pitch propellers. According to Alstom?s Tony Chronnell, the variable pitch propellers used on other coastguard cutters were not deemed efficient enough for ice impact. The cycloconverter controls the speed of the propulsion motors by varying the frequency of the power provided to the motors. A number of distinct advantages are gained using AC synchronous motors including smaller size and weight, excellent torque characteristics for icebreaking, and reduced maintenance. The vessel has a maximum speed of 17 knots, a more economical cruising speed of 12.5 knots and has icebreaking capabilities of 1.4m at a continuous 3 knots and about 2.5m by backing and ramming. Self sufficient Because the ship has been designed to operate at sea for up to six months, it has to be entirely self-sufficient or in a position to obtain specialist advice at a moment?s notice. To meet this requirement, Alstom designed and supplied an advanced remote technical support system which tracks all diagnostic information onboard the icebreaker obtained from some 5,000 data points located on every conceivable piece of engine room equipment to the machinery plant control and monitoring system. This is the main point for the ship?s data collection. It is used by the crew for information and equipment updates and for the collection of internal and external data, such as vibration recordings and oil analysis to build up a historical base for trend analysis. This in turn enables service engineers to recommend system optimisation, fine-tuning and upgrades in addition to predicting equipment failures and enabling preventative maintenance to be carried out. Under breakdown conditions, data can be transferred via satellite to Alstom?s UK-based offices in Rugby where engineers can quickly analyse data from the ship?s neural network and flag up possible changes in operating scenarios or potential equipment malfunction using sophisticated software tools. Ship control is provided at three conning stations with five conning positions. The conning stations are the pilothouse, which contains the Master Ship Control Console (MSCC) and port and starboard consoles, the aloft conn and the science conn. The MSCC consists of the integrated bridge system based on Sperry Marine?s VISION 2100 IBS, which incorporates the integrated navigation system (INS), steering control system, electronic chart display information system, and communications incorporating inputs from radar, speed log, gyrocompass, wind speed and direction, motion sensor, RDF, and TDP GPS. Sophisticated navigation equipment has been installed consisting of Sperry Marine?s Voyage Management System (VMS) which utilises multiple heading, position, environmental, and navigation inputs to steer the ship along a desired course. The vessel also has a number of GPS receivers including DGPS, P-Code GPS, Loran/GPS, 3-D GPS, and GLONASS/GPS. Heading inputs include two gyrocompasses and the 3-D GPS heading information. A Dynamic Positioning System (DPS) is available for station keeping and slow speed transits involving towing or dredging. The DPS was designed and built by Alstom and integrates the use of propellers, rudders, and the 1,840kW bow thruster to accomplish highly precise ship movement. Both of these systems allow for immediate changes to track plans and ship?s movement. On the communications side, Healy is fitted out with a wide range of communications equipment most of which is accomplished using the Inmarsat satellite system. Interestingly, due to the orbit location of the satellites serving this system, coverage may only be reliable to 75? North latitude. Beyond this point, communication has to be carried out using high frequency radio or other satellite services where available. Bottom profile For oceanographic research purposes, the vessel has a number of bathymetric survey systems installed including echo sound processor and depth digitizer, a seabeam bottom mapping sonar, acoustic Doppler current profiler and a Knudsen 320 B/R sub bottom profiler. This equipment allows for three dimensional imaging creating a realistic portrayal of the seabed. The USCG has been working with Nasa to develop an autonomous underwater vehicle capable of working under the icepack on future missions. Healy carries one 11.7m aluminium cargo carrying craft as part of normal outfit and, if a mission requires, it can carry a second cargo boat or an arctic survey boat based on the same design but with a cabin for limited science operations independent of the ship. These boats are launched by crane and require good environmental conditions for launch and recovery. The ship also carries two rigid hull inflatable boats (RHIB) that are 7m in length and are launched with Miranda type launch and recovery system which can be used in a wide variety of weather/sea conditions and can accommodate up to nine passengers. To complete an impressive list of equipment, the icebreaker is fitted with a flight deck, hangar, helo workshop and storeroom and accommodates two HH-65 helicopters. The primary function of the helicopters is to seek out the best route through the ice pack and guide the ship. As with most government run organisations these days, the US Coast Guard is under constant budgetary pressure to constrain its expenditure. Consequently Healy is operated by a crew of 67 which is nearly half the crew of the Coast Guard?s two older polar icebreakers. Having to operate in extreme climatic conditions, the vessel was designed and built to operate in temperatures as low as -45?C, to withstand 100 knot beam winds and cope with up to 17.75cm of topside ice. Although expensive, Healy is an extremely capable ship benefiting from the most up-to-date electronic equipment. The only major improvement the Coast Guard has in mind is the eventual retrofitting of the vessel with a podded propulsion system. At the time the vessel was designed back in 1992/3, pods were in their infancy and therefore a twin propeller configuration was adopted. Multipurpose solution with a difference The 6,370g Botnica, a combined icebreaker, towing and supply vessel, provides an interesting comparison with Healy. Built in 1998 for the Finnish Maritime Administration (FMA) by Aker Finnyards in Finland at a cost of around $60 million, the vessel operates as an icebreaker during the winter months and as a supply/towing/well-intervention vessel for the offshore industry during the summer. Completed in just 13 months, it differs from its predecessors, Fennica and Nordica, in its propulsion method. Both the previous ships use Wärtsilä medium speed diesels as their main propulsion plant. For Botnica it was decided to install an ?engine-generator-engine? diesel electric plant. This comprises six packages of twin Caterpillar 3512B units giving a total output of 12MW. These are connected to six ABB generators powering a Megastar controlled thrusters system of two 5MW Azipods driving 3.8m diameter four-bladed fixed pitch propellers at speeds up to 220 rev/min. The Azipods also support the icebreaking effort by creating a propeller wave which pushes the broken ice away from the hull and creates a wider channel of at least four times the width of the vessel. In addition, three 1,150kW Brunvoll bow thrusters are fitted to further enhance manoeuvrability. An open water speed of 15 knots is provided by the plant while the vessel can maintain 8 knots in 0.6m ice and four knots in 1.2m ice. For towing, Botnica has a 105t bollard pull capability. No idle downside The design challenge was to combine a cost effective vessel capable of using the maximum power needed for a front line icebreaker without the economic and environmental downside of running a massive slow speed engine at virtually idle power for offshore standby or positioning duties. By employing a diesel electric system and using the Azipod propulsion units, significant weight, space and maintenance benefits resulted as well as enhanced operational flexibility and redundancy. The security of power supplies and redundancy was enhanced by dividing the six gensets between two fully watertight engine rooms. In addition, the ability to vary the number of engines in service to meet the given power demand enhances the operational flexibility of the ship. All 12 engines can be run to meet maximum propulsion and auxiliary loads while running a single engine will often be sufficient for harbour power generation duties. In developing the hull form for the first of the trio Fennica, the designer, had to overcome the rolling movements of the traditional wide body icebreaker which would be excessively violent in rough North Sea conditions, particularly in beam seas, for safe offshore support deployment. To achieve good icebreaking performance with good sea keeping, the resulting unique hull form, which was also used for Botnica, provides optimum performance from the fore section of the hull for icebreaking while having exceptional stability from the aft section of the hull as required for offshore support duties. The unique characteristics of the 97m long by 24m wide hull shape are a broad bow to create the required ice channel, a narrow stern section giving the smallest possible water plane to reduce rolling, underwater bilge keels, reamers to break the ice when going astern and a plough stem for steering ice blocks sidewards. A combined stabiliser and anti-heeling tank system from Intering of Germany (now owned by Rolls Royce) was also fitted to enhance sea-keeping by achieving an average reduction in roll amplitudes of 40-60%. This anti-heeling system also assists in reducing friction between the hull and ice by inducing cyclic rolling. Conclusion It is difficult to draw a straightforward comparison between Healy and Botnica given the different multi-function requirements of both vessels, particularly when considering that Healy is, in some respects, a warship. On balance, however, Botnica, although smaller, represents better value for money and has the major benefit of being fitted with azimuthing pod propulsion units which, provided they maintain their reliability in service, give the vessel greater manoeuvrability, flexibility and economy for its multi functional role. It will be interesting to see by how much Healy?s performance improves as and when she is retrofitted with podded drives. Clearly, both vessels demonstrate the continued drive towards multipurpose ship types and perhaps one day an icebreaker will be designed that will have both offshore, escort and Arctic research capabilities. n