Design methodology and numerical analysis of a cable ferry

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1 Design methodology and numerical analysis of a cable ferry SNAME Annual Meeting; Nov 6-8, 2013, Bellevue, WA Paper #T35 Author name(s): Dean M. Steinke (M)1, Ryan S. Nicoll1 (V), Tony Thompson2 (M), Bruce Paterson3 (M) 1) Dynamic Systems Analysis Ltd., Dallas Road, Victoria, BC, Canada 2) EYE Marine, Suite 1, 327 Prince Albert Road, Dartmouth, NS, Canada 3) British Columbia Ferry Services, Inc., Blanshard Street, Victoria, BC, Canada

Nicoll1 (V), Tony Thompson2 (M), Bruce Paterson3 (M) 1) Dynamic Systems Analysis Ltd.

2 Presentation overview What is a cabled ferry? Project description Concept selection Requirements for dynamic analysis Analysis method Verification Frequency domain analysis Time domain analysis Ferry service assessment

dynamic analysis Analysis method Verification

3 What is a cable ferry? Used for centuries Cable is connected to both shores of a straight crossing Ferry is guided by cable to prevent lateral drift and heading change Various propulsion methods

4 Cable ferries 101 Used when bridge not warranted Must be straight crossing No navigation requirements as cables direct course Typical crossing length: m Modern passenger ferry: Wire ropes Hydraulically driven bull wheel

direct course Typical crossing length: 100 1500m Modern

5 Cable ferries 101 Often single drive cable More than one drive cable can be used Electric or hydraulic powering Lateral drift is resisted by pretension in cables Guide cables can be used Pretension ~1/5th of breaking load of cables Safety factor for quasi-static analysis typically 3

by pretension in cables Guide cables can be used Pretension ~1/5th of

6 Advantages of cable ferries Simple Efficient Barge shape Simple drive system A 42m 24 car ferry can maintain 7 knots with 50 kw hydraulic motor Operations Smaller crew and reduced maintenance

7 Disadvantages Limited maneuverability Cables may pose navigation hazard

8 BC Ferries project description Replacement of MV Quinitsa 2000m route, Baynes Sound

9 Proposed ferry description Length OA 80 m Beam (WL) 16 m Depth 2.1 m Draft m Mass 526 Tonnes Vehicle capacity (AEQ = Automobile Equivalent unit, 6.5m) 50 AEQ Vessel life 40 years

6 m Mass 526 Tonnes Vehicle capacity (AEQ =

10 Proposed ferry Two guide cables and one drive cable Dual lane offloading Central wheel house and passenger area Machinery located above main deck for accessibility and safety Service speed: 7.5 knots Proposed 300kW power Substantial deck overhangs to minimize deck wetness

above main deck for accessibility and safety Service speed: 7.

11 General arrangement

12 Ferry docking Pontoon docking Held by dolphin piles Cables run through pontoon either to anchors or winches Non-flat-bottomed vessel docking Adjusts to tides

13 Cables 200 kn pretension cables

14 Concept selection Checking weights, intact stability Preliminary bulkhead arrangement was determined to confirm adherence with floodable length standards Structural analysis Resistance calculation Hull optimization using strip theory approach Result: vessel meets existing regulatory standards

standards Structural analysis Resistance calculation Hull optimization

15 Why dynamic analysis? Longer route more exposure to high wind and waves Effect of cables on ferry motion must be considered Operator must ensure acceptable level of service Unique analysis: Not a typical moored platform Not a typical freely maneuvering vessel / barge

on ferry motion must be considered Operator must ensure acceptable

16 Dynamic analysis requirements Vessel / pontoon impact loads Operability Vessel / pontoon relative motion Ferry motions (accelerations and roll) Loads on shore structures Cable fairlead loads Cable loads Damaged condition loads Pretension determination Drive system power requirement Braking loads Centerline lateral drift Cable fatigue

structures Cable fairlead loads Cable loads Damaged condition loads Pretension

17 Dynamic analysis method Software used: ProteusDS Simulation capabilities needed: Finite-element cable model Interaction of cables with seabed bathymetry Winch model / control Vessel dynamics current, wave, and wind loading

model Interaction of cables with seabed bathymetry

18 Ferry hydrodynamic model ShipMo3D seakeeping analysis software Panel method Hydrostatics, wave excitation / radiation database 0.2 m^2 panel size (5600 panels) Export database of coefficients to ProteusDS

20 Finite-element cable model Cubic finite-element cable model Axial rigidity, drag and mass of cable is key Contact with seabed Parameter name Value Diameter m Mass per unit length 5.92 kg/m Axial rigidity/ea x 109 N

Contact with seabed Parameter name Value Diameter 0.

21 Winch and fairlead model PID controller mimics hydraulically driven traction winch Limits power and force Guide cables and a traction cable sliding connection model: Lateral stiffness and damping Allows translation of cable Reactions passed to ferry

22 Wind model verification Surge and sway loading matches Heave loading and yaw loading resisted by cable stiffness and hydrostatic forces so not as critical Surge drag: 1.15 Sway drag: 0.97

23 Seakeeping model verification Comparison of model tests carried out by Oceanic, NRC tank in St. Johns, NL Good match of ShipMo3D with tank tests, except roll Roll damping was adjusted

24 Design basis: Environmental conditions To examine the ferry performance, environmental conditions must be selected 1 year 100 year Extreme Significan 0.67 t wave height (m) Wave measurements made with a Peak 3.39 wave buoy and wave model of area period (s) Current 0.69 was developed Expected 1, 50 and 100 year extreme wind speeds were determined (historical records) Extreme current values Wave model used to hind-case hind cast conditions Wind speed (m/s) speed (m/s)

25 Frequency domain analysis Frequency domain forward speed RAO Cable stiffness included Reduce speed in head waves Yaw natural period 15 sec Waves < 4 sec RAO response at 4m/s forward speed and 90 deg absolute wave direction; note the yaw natural period due to the extra cable stiffness in the yaw response.

26 Time domain analysis Video

28 Ferry drift 92m with 200 kn pretension High pretension will reduce catenary snap loads Low pretension increase drift, winch issues

29 Summary of transit simulation results Condition Max Cable Load (kn) Drift (m) Roll ( ) Vertical Acceleration (m/s2) 100 Year Storm Extreme Storm Damage Case

30 Additional dynamic analyses Braking study Docking study Stopping distance: 65m (<1 ferry length) Check impact loads Check effect of relative roll Check effect of deflectors Fatigue analysis Rainflow Fatigue life >89 years

31 Ferry service Based on frequency of occurrence of waves and wind Criteria established for restricted operations Maximum of 35 trips per year (out of 12,400) may be affected Criteria Condition Vertical Acceleration <0.275g RMS at any point <0.10g RMS at any on the ship point within the passenger accommodation Restricted Operability Roll +/- 4 degrees RMS +/- 8 degrees Significant Restricted Operability +/- 2.5 Degrees RMS +/- 5 degrees Significant Caution Range Pitch +/- 1.5 degrees RMS +/- 3 degrees significant Restricted Operability Deck Wetness < 5% at the top of the bulwarks Restricted Operability

32 Conclusions The analysis of a 2000m cable ferry consisted of: Model basin resistance tests Wave basin roll motion tests Wind tunnel tests Frequency domain seakeeping analysis Environmental conditions analysis Time domain model verification transit simulations docking simulations braking simulations damaged condition simulations Cable fatigue analysis

33 Data determined from study Cable and shore loads due to ferry motion Ferry motion response in wind and waves Ferry interaction with pontoon Loads Relative motions Evaluated the environmental conditions at the site Drive system powering requirements Service levels

34 Acknowledgments BC Ferries Bruce Patterson E.Y.E. Marine Consultants Tony Thompson, Alistair Covill DSA Ryan Nicoll Oceanic Consulting Corporation

35 Thank you. For more information:

Design Methodology and Numerical Analysis of a Cable Ferry

Design Methodology and Numerical Analysis of a Cable Ferry Dean M. 1 (M), Ryan S. Nicoll 1 (V), Tony Thompson 2 (M), Bruce Paterson 3 (M) 1. Dynamic Systems Analysis Ltd., 101-19 Dallas Road, Victoria, BC, Canada 2. EYE Marine, Suite 1, 327 Prince Albert Road,