Boat Speed in Small Boats: The Physics of Going Faster

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The Big Picture in Winning Races. Boatspeed:A useful application of what you learned (?) in physics!. Fact: Dinghy sailors win in more types of boats than big boat sailors?. Background:. Why? Assuming you learned something more than starts and tactics in college!. Warning:.
Boat Speed in Small Boats: The Physics of Going Faster

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1. Boat Speed in Small Boats: The Physics of Going Faster Paul Miller Naval Arch & Ocean Engineering Dept. US Naval Academy

2. The Big Picture in Winning Races

3. Fact: Dinghy sailors win in more types of boats than big boat sailors?

4. Warning: ?Boatspeed Blindness? can be detrimental to your racing success!

5. 1996 Int?l Canoe Worlds Lemon Tree Passage, Australia

6. The Key Measurement of Racing Boatspeed V = Velocity of boat Vmg = Velocity of boat made good to the next mark (sometimes V ?to windward?) Which wins boat races? They are related by: Vmg = V * cos(f)

7. Example: Two Boats Beating

8. Solution

9. How do you find the optimum V and pointing angle, f?

10. VPP ?Polar?

11. Basic Physics of Boat Speed F=m*a ! The sum of the forces equals zero ?F=0 The sum of the moments equals zero ? M=0 or, ?For every action there is an equal and opposite reaction.?

12. Sail Force

13. In Detail:

14. Why is ?Acceleration? Important?

15. The Goal?s From Physics Are: Take as much from the wind as you can Reduce the mass of the boat as much as possible Disturb the water and wind as little as possible All the while making sure you are maximizing Vmg rather than V!

16. It isn?t quite that simple (but it?s close)! Quiz 1: Which is faster?

17. Boat A and Boat B

19. Sail Force Recall that ?For every action??

20. Sail Force The Magnitude of the force is approximated by Bernoulli?s Equation: F=??(air density)?(wind velocity)2?(Sail Area)?(Coef. of Lift)

21. Sail Trim The Direction of the Sail Force depends on how much Lift and Drag the sail is producing. Lift is the force produced perpendicular to the wind Drag is the force parallel to the wind.

22. Quiz #2 Which contributes more to boatspeed; Lift or Drag?

23. Upwind Sail Trim High Lift Full sail High Angle of Attack Even twist Low Drag Flat sail Low Angle of Attack Even twist

24. Downwind Sail Trim High Drag and Lift Full sail High Angle of Attack (near stall on reach, stalled on run) Even twist

25. Tell-Tales (Results from Wind Tunnel Tests)

26. Other Sail Controls Vang (twist, forestay tension, mast and boom bend) Outhaul (lower part of the main lift/drag control) Luff adjustment (flow attachment and lift coefficient control) Mast bend (spreaders, shroud tension)

27. How do you know when to adjust the controls? Is the twist even? Boom and top batten roughly parallel Is the boat overpowered? Can?t keep it flat, luffing sails What are the faster boats doing? If they are going faster than you, find out why!

28. The Ultimate Sail?

29. IACC/Int?l Canoe Mast Project

31. Foil Basics ?F=0 So Side Force generated by the sails is balanced by the side force (Lift) of the Foils (Centerboard and Rudder)

32. Foil Lift and Drag Centerboard and Rudder The same concept as sails Bernoulli?s Eqn for force (Lift or Drag) magnitude Vector addition of lift and drag components for direction Goal is high efficiency (High Lift/Drag ratio)

33. Foil Drag Components Friction (Viscosity) Pressure (Lift induced, eddies) Aspect Ratio (Span2/Area) Planform

34. Foil Frictional Drag Two things for sailors to think about: Smoothness (1/c Huffman: EN245A) Smoother the better Laminar vs Turbulent Min sand w/400 grit All coatings were worse Area

35. Example of Area Reduction

36. Foil Pressure Drag Keep angles of attack small so as to stay in low drag area of foil performance. (High Lift/Drag ratio)

37. Example of How to Minimize Angle of Attack

39. Hull Resistance Friction Pressure (eddies) Wave Making Spray

40. Typical Dinghy Resistance Curve

41. Hull Friction Drag Like foils, make it as smooth as possible! (Min 400)(Benefit is not as great as foils) Reduce area by heel or trim (flat areas out, round sections in)

42. Hull Pressure Drag Reduce eddies by not letting transom drag (look for ?clean? flow off stern) Move forward if possible

43. Hull Wave-Making Drag To make waves takes a lot of energy! Energy used in making waves is based on: Wave length Volume of water displaced

44. Example of Weight/Length Effect

45. Research in Length

46. ?New? Navy 44 Research

48. Stability The most important factor in speed? Effect of heel on drag Increased yaw moment Increased leeway Increased rig drag Increased wave making

50. How stability fits with physics ?F=0, ? M=0

51. Example: Effect of Hiking

52. Effect of Crew Weight on Speed

53. ?Nothing?s new in Naval Architecture?

54. So what do you do when you have too much wind, knowing that heeling is slow?! Options: Decrease Sail Area or Cl- Smaller sail, reef , twist or flatten Increase weight or ?t? - Bigger crew or hike farther out Decrease ?h? - ?Lower? sail or raise centerboard Increase B - Lower traveller, barber haul, ease sheet, twist sails

55. ?Something new in naval architecture?? (Actually proposed by L. F. Herreshoff in 1947)

56. Key points to remember about boatspeed: Reduce drag of sails, hull and foils Wetted surface, rudder angle, sail fullness, total boat weight Adjust power to match righting moment Proper twist Hike harder, sail flatter ?Flat is fast and fast is fun!?

57. Just for fun, what would happen if you got in the way of a Navy 44?

58. Have fun and think fast!


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