1. Wind and Tide Peter Bentley Technical Projects Manager
Skandia Team GBR

2. Wind and Tide You don't need a weather man
To know which way the wind blows
Bob Dylan
Subterranean Homesick Blues

3. Wind and Tide
What is the heading of a boat head to wind with the sails flapping?

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Answer

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Why does this situation occur? Because the wind is from 009 and because the tide is pushing boats down towards the committee boat.

6. Wind and Tide Sailing in tide - Which way does the wind blow?
Solutions:
Trigonometry
Vectors

7. Wind and Tide
Solutions:
Trigonometry
Vectors

8. Wind and Tide Vectors Vectors are easy!
The length of the line represents the magnitude of the action – speed of wind, tide, boat etc.
The angle of the line represents the direction the wind, boat, tide etc. is moving.
If we draw the lines so they touch at the ends, we can ‘add’ the vectors

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COG is a long way to the right of the sailing breeze!

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So how do we solve this problem?

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Where to put the mark (assuming we want zero bias)

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Happiness!

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But where to put the windward mark?

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For equal time on each tack it needs to go on the COG bearing…

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And here is a reminder why…

22. Wind and Tide Downwind: Which way does the wind blow?
Where shall we put the mark?
Trig too hard and prone to mistakes. Vectors easy and simple

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30. Wind and Tide Windward-Leeward Courses
Using just two buoys you can’s set a perfect beat and a perfect run in a cross-tide situation

31. Wind and Tide Windward-Leeward Courses Compromise
Using just two buoys you can’s set a perfect beat and a perfect run in a cross-tide situation
Compromise
In all but the most extreme situations it is possible to produce a good compromise

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Summary so far….

35. Wind and Tide Sailing Wind
The Sailing Wind is that experienced by a free-floating stationary boat

36. Wind and Tide Sailing Wind Upwind
The Sailing Wind is that experienced by a free-floating stationary boat
Upwind
The Sailing Wind is always influenced by the tide
The COG and SOG is always influenced by the tide
The two effects are additive

37. Wind and Tide Sailing Wind Upwind Downwind
The Sailing Wind is that experienced by a free-floating stationary boat
Upwind
The Sailing Wind is always influenced by the tide
The COG and SOG is always influenced by the tide
The two effects are additive
Downwind
The two effects are subtractive

38. Wind and Tide Startlines Unbiased starting lines are set at 90 degrees
to the sailing wind

39. Wind and Tide Startlines Course Axis
Unbiased starting lines are set at 90 degrees
to the sailing wind
Course Axis
Unbiased legs are set based on VMG with equal time on each tack

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What can go wrong?

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The Naive Race Officer

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44. Wind and Tide The Very Naive Race Officer
I’m not suggesting any of you would do this….. But
If using our original scenario, we put the windward mark directly upwind of the committee boat using a wind reference from the Committee boat (Ground Wind)
60 seconds on long tack
Time on short tack a) 40 seconds
b) 22 seconds
c) 17 seconds

45. Wind and Tide The Very Naive Race Officer
I’m not suggesting any of you would do this….. But
If using our original scenario, we put the windward mark directly upwind of the committee boat using a wind reference from the Committee boat (Ground Wind)
60 seconds on long tack
Time on short tack
c) 17 seconds

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Vector Changes

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Wind Shear
What is the Sailing Wind vector?

53. Wind and Tide Wind Shear What is the Sailing Wind vector?
A very difficult question to answer
Wind at mean rig height?
Split-tacks?

54. Wind and Tide Wind Shear What is the Sailing Wind vector?
A very difficult question to answer
Wind at mean rig height?
Split-tacks?
Well instrumented race-boats use split-tacks to set up the system calibration

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Taller weather-boat masts are one solution….

56. Wind and Tide Other Errors
Small hand-held wind meters (and some more expensive ones) have notoriously poor calibration, especially at low speeds.

57. Wind and Tide Other Errors
Small hand-held wind meters (and some more expensive ones) have notoriously poor calibration, especially at low speeds.
Shore based anemometers are often badly sited

58. Wind and Tide Other Errors
Small hand-held wind meters (and some more expensive ones) have notoriously poor calibration, especially at low speeds.
Shore based anemometers are often badly sited
Official reported winds are in degrees True. Sailors and race committees work in degrees Magnetic. Not generally a problem in the UK

59. Wind and Tide How significant are the Errors Goals
Unbiased start lines
Approximately equal time one each tack - upwind
Approximately equal time one each gybe - downwind

60. Wind and Tide Errors in course axis 5 degrees error
60 seconds on long tack
Time on short tack a) 60 seconds
b) 50 seconds
c) 40 seconds

61. Wind and Tide Errors in course axis 5 degrees error
60 seconds on long tack
Time on short tack a) 60 seconds
b) 50 seconds
c) 40 seconds
10 degrees error
b) 40 seconds
c) 30 seconds

62. Wind and Tide Errors in course axis 5 degrees error
60 seconds on long tack
Time on short tack a) 60 seconds
b) 50 seconds
c) 40 seconds
10 degrees error
b) 42 seconds
c) 30 seconds
18 degrees error
Time on short tack a) 40 seconds
b) 30 seconds
c) 20 seconds

63. Wind and Tide Errors in course axis 5 degrees error
60 seconds on long tack
Time on short tack
b) 50 seconds
10 degrees error
b) 42 seconds
18 degrees error
b) 30 seconds

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65. Wind and Tide
To Sum-Up
The tide has a significant effect on the sailing wind

66. Wind and Tide
To Sum-Up
The tide has a significant effect on the sailing wind
The tide has a significant effect on the Course Made Good

67. Wind and Tide
To Sum-Up
The tide has a significant effect on the sailing wind
The tide has a significant effect on the Course Made Good
These effects are not always easy or intuitive to work out

68. Wind and Tide
To Sum-Up
The tide has a significant effect on the sailing wind
The tide has a significant effect on the Course Made Good
These effects are not always easy or intuitive to work out
The errors introduced by these effects are very significant to the quality of the racing

69. Wind and Tide
To Sum-Up
The tide has a significant effect on the sailing wind
The tide has a significant effect on the Course Made Good
These effects are not always easy or intuitive to work out
The errors introduced by these effects are very significant to the quality of the racing
There are no hard and fast answers

70. Wind and Tide
To Sum-Up
The tide has a significant effect on the sailing wind
The tide has a significant effect on the Course Made Good
These effects are not always easy or intuitive to work out
The errors introduced by these effects are very significant to the quality of the racing
There are no hard and fast answers
As with so much involved in race officering, awareness and experience are the best tools

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Thanks for listening…..