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1. Boat Speed in Small Boats:The Physics of Going Faster Paul Miller
Naval Arch & Ocean
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 Intl Canoe WorldsLemon 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
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
For every action there is an equal and opposite reaction.
12. Sail Force
13. In Detail:
14. Why is Acceleration Important?
15. The Goals 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 isnt quite that simple(but its 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 Bernoullis 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 #2Which contributes more to boatspeed; Lift or Drag?
23. Upwind Sail Trim High Lift
High Angle of Attack
Low Angle of Attack
24. Downwind Sail Trim High Drag and Lift
High Angle of Attack (near stall on reach, stalled on run)
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?
Cant 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/Intl 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 DragCenterboard and Rudder The same concept as sails
Bernoullis 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)
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
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
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:
Volume of water displaced
44. Example of Weight/Length Effect
45. Research in Length
46. New Navy 44 Research
48. StabilityThe most important factor in speed? Effect of heel on drag
Increased yaw moment
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. Nothings 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
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!