Review of Engine Shafting, Propulsion and Transmission Systems Key Considerations for Industry

Transcription

1 Review of Engine Shafting, Propulsion and Transmission Systems Key Considerations for Industry By Dag Friis Bob McGrath Christian Knapp Ocean Engineering Research Centre MUN Engineering 1

2 Scope: Components of the Propulsion System Where engine power goes Propeller types Propulsive efficiency Cavitation Selection Guidelines What can I do with my as-installed system? Testimonials and Simulations Conclusions 2

3 Propulsion and Shafting System: Is a massive family that includes: Main Engine Gearbox Shafting Shaft couplings Journal and stern tube bearings Propeller Must be designed to work in harmony Changes or problems with one component effect the entire system 3

4 System Power Evaluation: Indicated Power Brake Power Shaft Power Delivered Power 4

5 Where Engine Power Goes: Gear Losses 4% Shaft Losses 3% Remaining 48% Prop Losses (thrust deduction) 25% PTO (if applicable) 20% 5

6 Propeller Types: Fixed Pitch Least Expensive in initial cost Efficient for wide range of operations 6

7 Controllable Pitch Propeller: Controllable Pitch Great for multi-mode operations. Engine RPM remains constant while pitch is varied for different loading conditions, or both simultaneously 7

8 Nozzles: KORT RICE Built Low Speed Efficiency Loses operational efficiency when majority of time spent steaming Built for Steaming Efficiency Multiple options by going with either speed or towing nozzle Depends on application and how much clearance you have if using a nozzle makes sense 8

9 Mewis Duct: Designed for vessels with poor inflow due to hull form Stabilizes water inflow to propeller. Uniform load distribution. Rotated fins pre-swirl the flow, generates higher load on propeller and more thrust Guaranteed efficiency gains (when designed and optimized for vessel and coupled with rudder technology) 9

10 Achieving Good Propulsive Efficiency: The Power characteristics of the engine have to be matched to the best possible propeller characteristics for this application. The main propeller characteristics are: Diameter Pitch RPM Number of Blades Blade Area Ratio 10

11 Achieving Good Propulsive Efficiency: The greater the propeller diameter the more efficient the propeller, i.e. choose the largest propeller that can be reasonably accommodated in the available propeller aperture. Propeller clearances (inches) Prop diameter (inches) minimum maximum minimum maximum minimum maximum a b c d

12 Cavitation: Cavitation occurs when the pressure in an area of the propeller falls below the vapour pressure. This results in bubbles or Cavities of steam forming The problem is that when the steam cavities collapse on the surface of the propeller it leads to erosion of the blade material Collapse also generates noise 12

13 Cavitation: TIP CAVITATION SHEET CAVITATION 13

14 Choice of Blade Area Ratio: The smaller the blade area ratio the higher the open water propeller efficiency The choice is made on the basis of choosing the smallest ratio that will give satisfactory propeller performance from a Cavitation point of view. 14

15 Hull and Propulsion System Interaction: Interaction Between Hull and Propeller Flow speed through the propeller (Wake fraction ) Effectiveness of the thrust developed by propeller (Thrust Deduction Fraction) Hull Geometry and Characteristics The higher the L/B ratio the better the flow of water to the propeller Results in a more gradual change in direction of water flow Lowers likelihood of flow separation and eddy making Increases flow velocity through propeller Results in more uniform flow velocity through propeller 15

16 Selection of Propeller Characteristics: In order to be efficient, the propeller characteristics have to be selected based on: Maximum Allowable Propeller Diameter Flow conditions at the propeller (hull form) Cavitation Operational Scenario Operating RPM (gear ratio) 16

17 Selection of Propeller Characteristics: Propeller type has to be selected based on operating regime: Fixed Pitch is best suited to a single speed operation Fixed Gear Fishery, i.e. Propeller Designed for Cruising Conditions Controllable Pitch when towing fishing gear Nozzle can be detrimental for boats that spend a major portion of their time steaming to and from the grounds due to the increased drag at cruising speed Nozzle Propeller when towing fishing gear, and affordable This is only likely to be the best alternative if the vessel spends most of its time towing gear Usually fitted with controllable pitch to optimize performance at both operating conditions 17

18 What can I do with my as-installed system? Have Clearance? Increase your diameter /decrease rpm(mind tip cavitation) No Clearance? Alter pitch and gear ratio (mind cavitation) Clearance AND Pitch restricted? Alter gearing ratio (mind cavitation and prop loading) Reduce unnecessary hotel loads (extra deep freezes, clothes dryers, T.V. s, cabin lights, etc) 18

19 Testimonials: 35 64'11" RPM VS Fuel Economy 30 GPH " Diameter 66" Diameter 86" Diameter RPM 86 diameter propeller achieving best fuel econ. and highest speed at lowest rpm 19

20 Testimonials: Identical 34'11" Vessels, Speed vs Prop Diameter at 660 RPM 10 9 Speed (kts) " Diameter 26" Diameter 28" Diameter Prop Diameter (in) 28 diameter propeller achieving highest speed at identical RPM 20

21 Simulations: 35 fixed gear vessel: Altered as-built prop from 25 to 30 diameter Achieved 12% fuel savings per hour 65 mobile gear vessel: Constrained in diameter due to as-built specs Achieved 2% fuel savings per hour by altering pitch Greater savings achievable by altering of gear ratio 21

22 Conclusions: Have your propeller checked by a qualified professional for suitability of Diameter, Pitch, RPM, and Blade Area Ratio and resulting efficiency for your operation If you are towing fishing gear a significant part of the time, a controllable pitch and possibly a nozzle propeller may be the best choice If you are not towing gear a well designed fixed pitch propeller is your best option Check that changing propeller and/or gear ratio makes economic sense for the remaining vessel life. Time and money spent in R&D can save and even make you money in the long term, but the analysis has to be done. Remember your decisions should make business sense. 22

23 QUESTIONS? VS 23

24 Propeller Cavitation Design Chart: 24

25 Considerations for Outboards: 25

26 Propeller Design Chart: 26

27 Symptoms and Causes: 27

28 Nozzle Propeller: If flow separation occurs around the nozzle one will get a significant increase in drag, i.e. reducing the efficiency of the nozzle-propeller Nozzle-Propeller diameter will be less than for regular propeller, therefore resulting a reduction in efficiency 28

29 Propeller Types: 29

30 Propeller Design Parameters: The Optimal Open Water Efficiency: Rises with increase of Propeller Diameter Rises with increase of Propeller Speed of Advance This is governed by hull characteristics and its effect on slowing of the water flow through the propeller disk (wake fraction) Decreases as the Blade Area Ratio Increases Governed by cavitation avoidance considerations 30

31 Achieving Good Propulsive Efficiency: The greater the propeller diameter the more efficient the propeller, i.e. choose the largest propeller that can be reasonably accommodated in the available propeller aperture. This is done by allowing for reasonable propeller clearances in order to reduce likelihood of pressure pulse vibrations being induced in the local hull structure. Propeller clearances (inches) Prop diameter (inches) minimum maximum minimum maximum minimum maximum a b c d