Yacht Design Technology

1. Yacht Design & Technology Model Testing

2. Lecture Contents When in yacht design process is model testing appropriate? What facilities are available? What are the testing and analysis techniques?

3. Introduction Prior to CFD, model testing was fundamental method for R&D of sailing yachts. Now physical experiments used in conjunction with CFD Still final arbiter of design choice

4. Facilities Large towing tanks Oceanic Consulting Corp, St Johns, Newfoundland, 200m long towing tank Qinetic, Gosport, UK, 258m long towing tank

5. Facilities Small towing tanks Southampton Institute, Southampton, UK, 60m long towing tank AMC, Tasmania, Australia, 60m long towing tank

6. Facilities Wind Tunnels Southampton University, Southampton, UK, High speed section: 2.1 m wide x 1.5m high x 4.4m long. Maximum wind speed: 50m/s. University of Maryland, USA Section: 4m wide x 2.5m high Maximum wind speed: 100m/s. University of Auckland, NZ Working section:�7m wide x 3.5m high x 5.5m long Maximum speed:�8.5 m/s

7. Facilities Wind Tunnels

8. Tank vs Wind Tunnel

9. Towing Tank Advantages of using large testing facility: Large model testing gives prospect of more reliable viscous behaviour, i.e. behaviour of boundary layer. This reduces scope for error in scaling viscous resistance. Effect of hull shape on viscous resistance & effect of keel, hull, bulb interaction more reliably investigated. Remember that boundary layer transition still needs to be forced using studs.

10. Towing Tank Advantages of using small testing facility: Easier to design dynamometer to cope with small forces of big models. Ease of model construction. Reduced testing time. Big cost reduction. Good for studies focusing on wave making resistance.

11. Wind Tunnel �Hydrodynamic� Keel, bulb and winglet tests 2. �Aerodynamic� Mast section tests and full rig and sail plan tests Flow visualisation Force measurement � dynamometer Sail tuning

12. Typical Investigations IAAC Extensive towing tank studies: relatively slow boats � viscous drag major consideration. Smaller models useful for canoe body, major appendage choices & seakeeping. Keel & bulb investigations in wind tunnel. Aerodynamic studies of mast, rigging & sail plans

13. Typical Investigations Volvo RTW Towing tank to develop hull form � fast & lightweight. Smaller models except for detail appendage work. Keel & bulb investigations in wind tunnel. Aerodynamic studies of mast, rigging & sail plans

14. Typical Investigations Open Classes Wide design scope. Low displacement & high Froude Numbers � wave making & balance effects dominate design process.

15. Typical Investigations IMS Designers aim is to beat IMS formulation, i.e. design boat that sails faster than predicted by IMS VPP.

16. Towing Tank - Technique Semi-captive technique, e.g. single post dynamometer: model free to heave � tow post runs on roller bearings model free to pitch � gimbal mechanism in tow fitting model constrained in heel � pin quadrant in heel fitting model constrained in yaw � yaw adjustment plate

17. Towing Tank - Technique Measure: heave motion pitch motion drag force roll moment lift force yaw moment

18. Towing Tank - Technique Error reduction: Construct accurate model. Use proven technique for forcing boundary layer transition. Consistent procedure to scale from model to full scale. Matrix of test conditions to allow hydrodynamic characteristics of model to be determined & performance predicted by VPP.

20. Recap/Reflect Sum over one complete wave period all local damping waves generated by number of sections along yacht length. Sum over one complete wave period all local damping waves generated by number of sections along yacht length.

21. Sum over one complete wave period all local damping waves generated by number of sections along yacht length. Sum over one complete wave period all local damping waves generated by number of sections along yacht length.