Yacht Design

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Yacht Design Technology

• Model Testing

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Lecture Contents

• When in yacht design process is model testing
  appropriate?
• What facilities are available?
• What are the testing and analysis techniques?

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Introduction

• Prior to CFD, model testing was fundamental
  method for RD of sailing yachts.
• Now physical experiments used in conjunction with
  CFD
• Still final arbiter of design choice

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Facilities

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

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Facilities

• Small towing tanks
• Southampton Institute, Southampton, UK,
• 60m long towing tank
• AMC, Tasmania, Australia,
• 60m long towing tank

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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

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Facilities

• Wind Tunnels

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Tank vs Wind Tunnel
 
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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.

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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.

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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

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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

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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

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Typical Investigations

• Open Classes
• Wide design scope. Low displacement high Froude
  Numbers wave making balance effects dominate
  design process.

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Typical Investigations

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

High budget campaigns may conduct tank studies to
improve on wave making resistance predictions
seakeeping. Also wind tunnel for keel/bulb
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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

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Towing Tank - Technique

• Measure
• heave motion
• pitch motion
• drag force
• roll moment
• lift force
• yaw moment

• Although minimal interaction between forces is
  designed for in dynamometer, it is necessary to
  calibrate cross talks
• roll into lift cross talk
• yaw into drag and lift cross talk

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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.

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Recap/Reflect
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