Wind and Tide Peter Bentley Technical Projects Manager Skandia Team GBR
Wind and Tide You don't need a weather man To know which way the wind blows Bob Dylan Subterranean Homesick Blues
Wind and Tide What is the heading of a boat head to wind with the sails flapping?
Wind and Tide Answer
Wind and Tide Why does this situation occur? Because the wind is from 009 and because the tide is pushing boats down towards the committee boat.
Wind and Tide Sailing in tide - Which way does the wind blow? Solutions: Trigonometry Vectors
Wind and Tide Solutions: Trigonometry Vectors
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
Wind and Tide
Wind and Tide
Wind and Tide
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Wind and Tide
Wind and Tide COG is a long way to the right of the sailing breeze!
Wind and Tide So how do we solve this problem?
Wind and Tide Where to put the mark (assuming we want zero bias)
Wind and Tide Happiness!
Wind and Tide But where to put the windward mark?
Wind and Tide For equal time on each tack it needs to go on the COG bearing…
Wind and Tide And here is a reminder why…
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
Wind and Tide
Wind and Tide
Wind and Tide
Wind and Tide
Wind and Tide
Wind and Tide
Wind and Tide
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
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
Wind and Tide
Wind and Tide
Wind and Tide Summary so far….
Wind and Tide Sailing Wind The Sailing Wind is that experienced by a free-floating stationary boat
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
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
Wind and Tide Startlines Unbiased starting lines are set at 90 degrees to the sailing wind
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
Wind and Tide
Wind and Tide What can go wrong?
Wind and Tide The Naive Race Officer
Wind and Tide
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
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
Wind and Tide Vector Changes
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Wind and Tide
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Wind and Tide Wind Shear What is the Sailing Wind vector?
Wind and Tide Wind Shear What is the Sailing Wind vector? A very difficult question to answer Wind at mean rig height? Split-tacks?
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
Wind and Tide Taller weather-boat masts are one solution….
Wind and Tide Other Errors Small hand-held wind meters (and some more expensive ones) have notoriously poor calibration, especially at low speeds.
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
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
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
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
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
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
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
Wind and Tide
Wind and Tide To Sum-Up The tide has a significant effect on the sailing wind
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
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
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
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
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
Wind and Tide Thanks for listening…..