Fast Ferry Powering and Propulsors The Options

Transcription

1 Fast Ferry Powering and Propulsors The Options By Nigel Gee Managing Director Nigel Gee and Associates Ltd, UK SUMMARY In the 1970 s and 1980 s, fast ferries were used to transport passengers only and most were propelled by a pair of industry standard 16 cylinder diesel engines each driving a waterjet. The size of these vessels was mainly suitable for passengers and with speeds of knots. Today, passenger ferry sizes have increased and speeds up to 60 knots are now possible. During the 1990 s in excess of 100 fast car/passenger ferries have been introduced into service. The speed of development possibilities for the future are to an extent governed by available prime movers and propulsors. With increasing size and speed, high installed powers are required and this has lead to multiple prime mover and propulsor installations. This paper examines some of the engine and propulsor options open to designers, builders, and operators, and shows how powering and propulsor choices have been made through a number of case studies. AUTHORS BIOGRAPHY Having graduated with an Honours Degree in Naval Architecture from Newcastle University in 1969 and, in the same year, completed a shipyard apprenticeship sandwich course with Swan Hunter Shipbuilders in Newcastle, England, Nigel Gee entered a career in the Naval Architecture of high speed and novel ship and boat forms beginning with Burness Corlett & Partners, Consultants, in Hampshire, England, moved to manufacturing industry with Hovermarine in 1971 being promoted to Engineering Manager in Left Hovermarine to pursue an academic career in 1979 as Senior Lecturer in Naval Architecture and Fluid Mechanics at the Southampton Institute. Lectured to First Degree level and undertook a number of research projects linked with industry. In 1983 returned to industry with the Vosper Group as Technical General Manager of a department with 60 technical personnel. Left in 1986 to start the design company Nigel Gee and Associates Ltd. Since 1986 the company has undertaken designs for over 120 built fast vessels. These vessel designs range from 10m, 30 knot crew boats, to 200m, 25 knots fast container ships. In the field of fast ferries, the company has produced designs for a number of SES and catamaran designs including two 36 knot ferries introduced into service in New York Harbour in 1997, and a 55 knot vessel which entered service in 1

2 Argentina in January A number of designs have been produced for fast car and passenger ferries and fast freight vessels. Design is in progress for a fast car ferry due for delivery in mid 2002 and ten vessels have been constructed to the company s design for a 25 knot fast feeder container vessel. Further designs for fast freight vessels with speeds from knots are in progress. Nigel Gee is a Fellow of the Royal Institution of Naval Architects and a Member of the Society of Naval Architects and Marine Engineers. 1. ENGINE OPTIONS Engine options for powering large fast passenger craft, or fast Ro-Pax craft have been examined. Only engine powers in excess of 2000kW per single engine have been considered. The high speed diesel engines, medium speed diesel engines and gas turbine engines normally considered for fast ferry powering are listed in Tables 1, 2 and 3. These are manufacturers data for dry engines without gearbox. Footprint is calculated from the engine overall length by overall width. Specific Fuel Consumption s (SFC s) are manufacturers quotations in ISO conditions. Figure 1 shows the distribution of high speed and medium speed diesels and gas turbines according to power ranges in steps of 2MW. It can be seen that a range of high speed diesels are available to cover powers from 2-10MW with the number of engine choices in each power band falling with increasing power. Similarly, for medium speed diesels there is a wide range of engines available up to 20MW, and then further single engines available up to a maximum of 36MW. Multiple gas turbine choices are concentrated in the range 2-6MW with individual engines covering a number of higher ranges. There is a significant gap in the availability of gas turbines for powers from 8-14MW which is becoming an increasingly common fast ferry power demand. It is of course possible to fulfil this demand by using multiple engines, albeit with more complexity and possible use of heavy combining gearboxes. Figures 2, 3 and 4 are plots of engine power to weight ratio for a range of powers. Figure 2 shows all the diesel engines and Figure 3 the gas turbines. Power to weight ratios are compared for diesels and gas turbines in Figure 4. It can be seen that the power to weight ratio of the gas turbines is very significantly higher than the diesels, generally ranging between 25 or 40 times as high for gas turbines. Similarly, Figures 5, 6 and 7 show power to footprint ratio, and once again the gas turbine engines are superior, generally having power to footprint ratios three to five times greater than those for diesels. Of course, footprint is not the only consideration when looking at the volume requirements for engine rooms, and the increased volume of intake and exhaust systems and intake air filtration systems required for gas turbines, often means that there is little difference in the volumetric requirements for gas turbine and high speed diesel engines, particularly in smaller high speed passenger ferries. 2

3 In general, it can be stated that the weight of gas turbine installations will be very significantly less than for diesel installations, and volumes may be less particularly in larger power installations. On the basis of weights and volume alone, gas turbines would be favoured. Figure 8 shows a comparison between specific fuel consumption for the range of gas turbines and diesels, and it can be seen that at any given power level gas turbine SFC s are higher than diesel SFC s. Of course it is also true that gas turbine installations require less power for a given vessel speed, because of their lower weight contributing to a lower displacement for the vessel. If less power is installed then there is an effective saving in SFC and this is shown in Figure 8. Nevertheless, in general even this reduction in fuel consumption is insufficient to offset the increased SFC of the gas turbine in most cases. Table 4 shows some typical vessel displacements and machinery weights for a range of vessels designed by Nigel Gee and Associates. In each case, the percentage reduction in displacement which could be achieved by substituting gas turbines for diesels is shown together with the percentage SFC increase. In four of the five cases, the SFC increase more than offsets the displacement reduction. In the case of the very large 40 knot ro-pax, there is a larger displacement reduction than SFC increase. This particular vessel has an installed power in excess of 100MW, which accounts for the large reduction in weight and at this power, gas turbines fuel consumption is approaching that of large diesel engines. These figures must be viewed with some caution since the weight of the engine and gearbox only has been considered and not the associated inlet and exhaust. Nevertheless, there is a clear indication that for larger vessels the installation of large lightweight efficient gas turbines could have advantages in fuel consumption as well as weight and volume. A criterion often advanced for assisting in the choice between diesel and gas turbine installation is that of range. Figure 9 shows the variation of speed with range for a vessel fitted with alternative diesel or gas turbine installations of the same power. Clearly, the gas turbine vessel will have a lower empty weight and, therefore, a higher speed at low range. However, since the fuel consumption is higher, then as range increases, the amount of fuel carried increases to the point where at a certain range the gas turbine vessel is actually heavier than the diesel vessel and its speed lower. The preliminary conclusion would be that at up to the critical range the gas turbine installation would be selected and above the critical range the diesel selected. However, if the power of the diesels are increased to give the same empty speed, then because the percent weight increase is normally less than percent SFC saving the diesel vessel will show benefit throughout the range. Weight, volume and SFC are of course only part of the story. Table 5 lists other considerations which owners and operators will need to look at before deciding on a particular engine installation. The figure is self-explanatory and perhaps the main features are the purchase and maintenance costs and the reliability, availability and maintainability of the chosen units. The case studies in Section 3 of this paper show how these considerations often become dominant in engine choice. 3

4 2. PROPULSORS Table 6 shows the propulsor options of fast ferries, together with an indication of the maximum efficiency that might be expected, and some qualitative descriptions of the potential advantages and disadvantages of a particular propulsive device. For most small vessels, the choice is between propeller or waterjet and the selection will normally be made on the basis of speed. Vessels having a speed capability over 35 knots are most likely to have waterjet propulsion because high efficiencies are still possible. Propeller efficiencies at these higher speeds are diminishing and propeller sizes may become unmanageable on small lightweight high speed vessels. For very large vessels electric podded propulsion is becoming a significant option. 3. CASE STUDIES Table 7 below lists six vessels designed by Nigel Gee and Associates which are used to illustrate some of the criteria used in selecting prime movers and propulsors for these vessels. 3.1 Case Study 1 This is a 30m, 45 knot passenger vessel (see Figure 10) currently at the detailed design stage and due for delivery in The vessel is designed to meet a requirement for a very small craft to achieve high speeds with a high degree of passenger comfort when operating in sea state 3-4. To achieve the speed and comfort required, it is necessary to fly the vessel on a combination of foils and buoyant pods. The hull design of the vessel is based on the NGA Patented Pentamaran form, with a combination pod and lifting hydrofoils spanning the aft sponsons, and a T-Foil at the bow which also contributes net lift to the system The main problem with such a vessel is the high vertical distance between the prime mover and the propulsive device. Choices for this application are either a propeller driven through a V box and steeply angled shaft, a waterjet with a deep scoop, or a Z-drive. In this particular case, the propeller solution was regarded as relatively high risk, mainly from the point of view of the cavitation of a propeller running at knots on a high angled shaft. Waterjets were rejected because of the lower efficiency associated with lifting water from the intake scoop to the hullmounted waterjet, and the drag of the scoop itself. Because the power of this vessel is quite low (approximately 2.3MW) an Ulstein Speed-Z unit was chosen as the propulsor. These units have been fitted to a variety of high speed craft including SES, catamarans and foil catamarans. The necessity to keep weight to an absolute minimum and the very limited space involved in the single slender hull led to a gas turbine being selected as the prime mover despite the higher fuel consumption. 4

5 3.2 Case Study 2 This vessel is designed to carry 400 passenger at 40 knots in sea state 3 on a 30nm route. The design requirement and choices made are summarised in Figure 11. For this vessel a number of powering options were considered, three of which are shown in Figure 12. Speeds of between knots were considered. The final selection was for 2 x TF50 gas turbines driving waterjets. It is interesting to note that a solution using four diesel engines would have yielded a slightly higher speed at a lower overall fuel consumption, but nevertheless the gas turbine solution was selected. The operator wished to have the facility to run at 100% MCR reasonably frequently and also preferred gas turbine maintenance routines. 3.3 Case Study 3 Figure 13 shows the prime mover and propulsor selection for a 55 knot passenger vessel built during 1999 for Buquebus. Once again despite superior fuel consumption figures for a diesel solution the operator selected gas turbines. The decision was made on a complex mix of space, weight and vessel trim considerations. When considering costs it is significant that this operator s major competition on routes across the River Plate are aircraft and, therefore, fuel cost considerations may not be as significant on some other routes. 3.4 Case Study 4 This vessel is shown in Figure 14 and is currently in detail design destined for delivery in late The vessel carries 300 passengers and 40 cars and has a maximum speed of 40 knots. Fuel economy was of paramount importance on this vessel and four diesel engines were selected. 3.5 Case Study 5 This vessel is a 40 knot large ro-pax ferry and at the preliminary design stage for a Mediterranean customer (see Figure 15). The vessel can carry 800 passengers and 200 cars at 40 knots. The prime mover selection on this vessel is further complicated by the possibility of building the vessel is either aluminium or steel. For the same speed and payload the aluminium hull/gas turbine propelled vessel will have better fuel economy than a steel vessel fitted with medium speed diesel engines. The potential operator for this vessel is currently weighing the trade-off between better fuel economy and higher purchase cost of the vessel. 5

6 3.6 Case Study 6 This vessel is certainly not fast having a top speed of 12 knots (see Figure 16). It is included as a case study to illustrate another set of design drivers on prime mover and propulsor selection. This ro-pax vessel is very small (approximately 35m) it has to carry a high load of 16 cars or 2 x 38 tonne articulated trucks at speeds of 12 knots in seas with a maximum wave height of 5m. Installed power levels on the vessel are driven by the berthing requirement in Beaufort 10 winds, rather than by the free-running speed of 12 knots. As well as a high power required for berthing, very high side thrusts are required, which has led to the selection of azimuthing pods for main propulsion and very large twin bow thrusters. The huge power range and high cyclic loading demanded by frequent berthings and very short passage times has led to the selection of diesel electric machinery. Small high speed diesel engines were selected on space and cost grounds. 4. CONCLUSION This short paper and selection of case studies has indicated that prime mover and propulsor selection is normally made on the basis of a wide range of owner/operator requirements and rarely restricted to simple considerations of weight, space and fuel consumption. 6

7 Table 1.- Engine Power Comparison Table High Speed Diesel (Ferry Rating; ISO Conditions: air & water temp. 25 o C) Power Weight Footprint Power/Wt Power/Footp'nt SFC Type kw kg m 2 kw/kg kw/m 2 gr/(kw.hr) (Dry) (LxB) (ISO rating) MTU 16V 396 TE74L Ruston 8RK270HF Paxman Valenta CM 12V Cummins-Wärtsilä CW170 16V Ruston 6RK Paxman VP185 12V MTU 16V 4000 M Cummins-Wärtsilä CW170 18V Cummins-Wärtsilä CW200 12V Paxman Valenta CM 16V Ruston 8RK Ruston 12RK270HF Paxman Valenta CM 18V Cummins-Wärtsilä CW200 16V Paxman VP185 18V Cummins-Wärtsilä CW200 18V Pielstick 12 PA6 STC MTU 16V 595 TE70L Ruston 16RK270HF Ruston 12RK Pielstick 12 PA6 B STC Ruston 20RK270HF Pielstick 16 PA6 STC MTU 16V 1163 TB73L Ruston 12RK CAT MTU 20V 1163 TB Ruston 16RK Pielstick 16 PA6 B STC MTU 20V 1163 TB73L MTU 16V 8000 M Ruston 16RK MTU 16V 8000 M CAT Ruston 20RK Pielstick 20 PA6 B STC MTU 20V 8000 M Ruston 20RK MTU 20V 8000 M

8 Table 2.- Engine Power Comparison Table Medium Speed Diesel (Ferry Rating; ISO Conditions: air & water temp. 25 o C) Power Weight Footprint Power/Wt Power/Footp'nt SFC Type kw kg m2 kw/kg kw/m2 gr/(kw.hr) (Dry) (LxB) (ISO rating) Ruston 12RK Wärtsilä 32 6R Wärtsilä 32 6L Ruston 16RK Wärtsilä 32 8R Wärtsilä 32 8L Wärtsilä 32 9R Wärtsilä 32 9L CAT Wärtsilä 38 6L-B Sulzer ZA40S 6L Wärtsilä 26X 12V Wärtsilä 32 12V-E Wärtsilä 32 12V Wärtsilä 38 8L-B Sulzer ZA40S 8L Wärtsilä 46 6L-C Wärtsilä 26X 16V Wärtsilä 38 9L-B Wärtsilä 32 16V-E Sulzer ZA40S 9L Wärtsilä 26X 18V Wärtsilä 32 16V Wärtsilä 32 18V-E Wärtsilä 32 18V Wärtsilä 46 8L-C Wärtsilä 38 12V-B Pielstick 12 PC 2.6 B Sulzer ZA40S 12V Wärtsilä 46 9L-C Wärtsilä 64 5L Pielstick 14 PC 2.6 B Sulzer ZA40S 14V Wärtsilä 38 16V-B Pielstick 16 PC 2.6 B Sulzer ZA40S 16V Wärtsilä 64 6L Wärtsilä 46 12V-C Wärtsilä 38 18V-B Pielstick 10 PC4.2B Sulzer ZA40S 18V Wärtsilä 64 7L Pielstick 20 PC 2.6 B Pielstick 12 PC4.2B Wärtsilä 64 8L Wärtsilä 46 16V-C Wärtsilä 64 9L Wärtsilä 46 18V-C Pielstick 16 PC4.2B Wärtsilä 64 12V Pielstick 18 PC4.2B Pielstick 20 PC4.2B Wärtsilä 64 16V Wärtsilä 64 18V

9 Table 3.- Engine Power Comparison Table - Gas Turbines (ISO Conditions: 15 o C, 1.013mbar, 60% relative humidity) Type Power Weight Footprint Power/Weight Power/Footprint SFC kw kg m 2 kw/kg kw/m 2 gr/(kw.hr) (Ferry Rating) (LxB) (ISO rating) Rolls Royce UT Allied Signal TF Pratt & Whitney ST30 Dry Allied Signal TF50A Pratt & Whitney ST40 Dry GE LM Solar Taurus 60M Rolls-Royce 501-KF Rolls-Royce 601-KF Rolls-Royce 601-KF GE LM ABB GT Rolls-Royce Spey GE LM GE LM GE LM6000PC Rolls-Royce Trent

10 Table 4.- Engine Weight & SFC Comparisons Involving NGA Designs Ferry Type & Application Diesel Full Load Displacement (tonnes) Diesel Engine + GB Weight (tonnes) GT Engine + GB Weight (tonnes) % Displacement Reduction % SFC Increase 35 knot Passenger Ferry NYFF knot Passenger Ferry BUQUEBUS knot Ro-Pax PECAN (HSD) knot Ro-Pax PECAN (MSD) knot Ro-Pax SEABRIDGE

11 Table 5. Other Considerations Will Diesels Fit? Small boats, high powers Slender craft Cost / kw Maintenance Costs Can A Lightweight Diesel Provide High Enough Power High speed diesel limit 10 MW Medium speed diesel limit 35 MW Gas turbine 50 MW (90 MW Soon!) Reliability, Availability, Maintainability Frequency of Need To Use 100% MCR

12 Table 6.- Propulsor Options Propulsor Type Preferred Speed Range (knots) Maximum Efficiency Advantages Disadvantages Propeller up to Low Cost Waterjet Surface Propeller Electric POD Drives up to * - Compact - Low Vulnerability - Steerable - High Efficiency at very high speeds - Steerable - Very high efficiency - Flexibility for type alocation of prime movers - High diameter - Vulnerability - High Cost - Few commercially proven systems - High cost Z-Drives up to * Airscrews High efficiency - Deep shaft line - For Hydrofoils and POD supported boats (no water contact required) - Limited Power & Torque torque range - Low efficiency - Noise (*) Excludes Strut Drag

13 Table 7. Case Studies knot Small Passenger Vessel knot Passenger Vessel knot Passenger Vessel knot Ro-Pax Ferry knot Large Ro-Pax 6. Small Diesel - Electric Ro-Pax Vessel

14 Figure 1.- Marine Propulsion Engines For Fast Ferries The Ranges Gas Turbines Medium Speed Diesel High Speed Diesel

15 Figure 2.- Power/Weight Ratio As A Function of Power - Diesel High Speed Diesels 0.30 Power/Weight (kw/kg) Medium Speed Diesels Power (kw)

16 Figure 3.- Power/Weight Ratio As A Function of Power Gas Turbine Large scatter in data is caused by differences in the way manufacturers quote gas turbine weight. Some include acustic insulation, some others don't Power/Weight (kw/kg) Power (kw)

17 Figure 4.- Comparison of Power/Weight Ratio Between Diesel And Gas Turbine Power/Weight (kw/kg) Diesel Gas Turbine Power (kw)

18 Figure 5.- Power/Footprint Ratio As A Function of Power - Diesel Power/Footp'nt (kw/m 2 ) Power (kw)

19 Figure 6.- Power/Footprint Ratio As A Function of Power Gas Turbine Large scatter in data is caused by differences in the way manufacturers quote gas turbine weight. Some include acustic insulation, some others don't Power/Footp'nt (kw/m 2 ) Power (kw)

20 Figure 7.- Comparison of Power/Footprint Ratio Between Diesel And Gas Turbine Power/Footp'nt (kw/m 2 ) Diesel Gas Turbine Power (kw)

21 Figure 8. SFC Comparison Between Gas Turbine and Diesel SFC (gr/(kw.hr)) Effective Reduction in SFC by Weight and Power Saving Gas Turbine Diesel Total Installed Power (MW)

22 Figure 9. Speed Variation With Range for Diesel and Gas Turbine Same Installed Power Diesel & Gas Turbines Normal expected range where % Wt increase < % SFC saving Speed at Full Load Displacement Increased power Diesels where % Wt increase > % SFC saving Increased power Diesels where % Wt increase < % SFC saving GAS TURBINE DIESEL Range

23 Figure 10. Case Study 1 45 knot Small Passenger Vessel Design Requirement 149 passengers; 40/45 knots. Sea state 4; High comfort level. Hull Form Selected Stabilised monohull (Pentamaran) with submerged Pods. Weight critical design. Power Required 2 / 2.5 MW. Gas turbine selected on weight and space criteria. Propulsor Vessel flies, needs high vertical separation between prime mover and propulsor. Waterjet and scoop or Z-Drive. Z-Drive available and gives higher efficiency Designer s Note: Limited range of Z-Drives or other propulsors available for this type of application

24 Figure 11. Case Study 2 40 knot Passenger Vessel Design Requirement 400 passengers - 40 knots Sea state 3 Hull Form Selected Round bilge catamaran Power Required 7.2 MW (gas turbine) 8.1 MW (diesels) Diesels 12½ % higher power But gas turbines SFC 30% higher Operator Choice TF50 gas turbines Wants to run 100% MCR, often prefers gas turbine maintenance routine Propulsor KaMeWa waterjets

25 Figure 12. Case Study 2; Power Requirements Power Required - 4 x MTU 16V4000 Power Required - 2 x TF Power Required - 2 x TF x TF80 Turbines Required Power (kw) x MTU MTU 16V V x TF50 Turbines Vessel Speed (knots)

26 Figure 13. Case Study 3 55 knot Passenger Vessel Design Requirement 55 knot top speed 50 knot cruise at full load in sea state 3 Hull Form Selected Hard chine catamaran Power Required 13.0 MW diesel 11.0 MW gas turbine Diesels 18% higher power But gas turbines SFC 30% higher Operators Choice Propulsor TF80 (2 x TF40) gas turbines Decision based on space weight and trim considerations Hull form allows side-by-side installation MJP waterjets

27 Figure 14. Case Study 4 40 knot Ro-Pax Ferry Design Requirement 350 passengers and 40 cars; 40 knots Hull Form Selected Round bilged catamaran Power Required 9.0 MW diesel 7.5 MW gas turbine Operators Choice Diesel for fuel economy 4 x MTU 4000 M70 Propulsor Waterjets

28 Figure 15. Case Study 5 40 knot Large Ro-Pax Ferry Design Requirement 800 passengers and 200 cars; 40 knots Hull Form Selected Pentamaran Power Required Aluminium / gas turbine 22 MW Aluminium / high speed diesel 25 MW Steel / medium speed diesel 28 MW Aluminium / gas turbine 22% less power Steel / medium speed diesel 18% less SFC Aluminium/gas turbines better fuel economy - but higher cost Operators Choice Under discussion Propulsor Waterjet

29 Figure 16. Case Study 6 Small Diesel-Electric Ro-Pax Vessel Design Requirement 16 cars or 2 x 38t articulated trucks and 100 passengers; 12 knots Maximum length 35m Sea state 4/5; Beaufort 10 Hull Form Selected Full form monohull Power Required 2.0 MW (docking condition) Steerable thrusters with very high bow thrust requirement Diesel / electric solution Engines Selected High speed diesels - 3 installed, 2 running Propulsors Selected Aquamaster