Theoretical Maximum Boat Speed?

Discussion in 'Laser Talk' started by drjoefo, Jul 4, 2007.

  1. drjoefo

    drjoefo New Member

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    Is there a maximum speed a hull can travel at? If so, what is it limited by? E.g Length of waterline:rolleyes:

    P.s. Theoretical is possibly spelt wrong
     
  2. sorosz

    sorosz Member

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    Maximum hull speed is 1.34 X square root of the length of the waterline. The Laser is 13'9" length overall so say about 13' 6" at the waterline. That gives you a theoretical maximum hull speed of 4.9234743 knots.
    Hull Speed Calculator

    That's why planing is good since it gets you up and over the bow wave and frees you from that constraint. Essentially a boat's displacement mode (ie hull speed) is limited by the bow and quarter waves which are determined by the waterline length. Good, basic references like Chapman's and Annapolis Book of Seamanship (among others) have better and more detailed explanations.
     
  3. drjoefo

    drjoefo New Member

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    so the rule only applies to displacement hulls and not dinghys that can plane ?
    - what is the definition of planing ? when your boat speed exceeds that of the bow wave ?

    thanks a bunch.
     
  4. sorosz

    sorosz Member

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    A planing hull is in displacement mode when it is not planing, so hull speed is limited then. Once the boat increases speed enough to climb up and over its bow wave then it begins planing.

    The simple dictionary definition of planing is "skimming across the water", but your definition is probably just as good for the task at hand. The definition below might help make more sense:

    From Chapman's Glossary p902 64th ed.:
    Planing Hull A hull designed so that forward speed creates water lift, reducing friction and increasing speed.
    More from Chapman's . . .
     
  5. phosphor

    phosphor Member

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    I don't think there is a simple mathematical way to determine your max speed when planing. Would there be a point when the skin friction becomes too great and can't be overcome? Hmmm.... I'll let you know if I ever come across anything in my studies. I'd guess someone somewhere figured out the equations but I have no doubt that it's wicked complex.
     
  6. Josef

    Josef New Member

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    The theoretical speed of a planing boat with unlimited wind and waves and perfect crew work is only limited by the equipment, you can go faster untill it breaks =P
     
  7. drjoefo

    drjoefo New Member

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    Does that mean that the boat can go so fast as to leave the bow wave all togeather?
     
  8. Old Geezer

    Old Geezer Member

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    Sure. When Michael Blackburn crossed the Bass Strait in a Laser his max speed was 19.7 knots. And he averaged 8.6 knots for 117 miles. He esitimated that he caught a wave every 10 seconds for 13.5 hours.
     
  9. KdaP

    KdaP New Member

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    although it sounds silly, i have to ask:
    why dont they make boats with a really big sail and really big racks for trapezing off ?
     
  10. Wavedancer

    Wavedancer Upside down? Staff Member

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    There are lots of those; they just aren't Lasers
     
  11. John Gilmour

    John Gilmour Member

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  12. GeoffS

    GeoffS Member

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  13. GeoffS

    GeoffS Member

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    Likely the limiting effect would be keeping the hull in contact with the water.

    So far as I (and Wikipedia) know, the fastest boat was clocked at 511 km/h (317 mph).

    Cheers,

    Geoff S.
     
  14. phosphor

    phosphor Member

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    Isn't is impossible to leave the bow wave all together without being a WIG? Or maybe hydrofoils maybe, but anyways... I think of it as you climb over the bow wave, it simply moves farther and farther aft. You can't stop creating one...
     
  15. drjoefo

    drjoefo New Member

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    Thats exactley what I was thinking.
     
  16. Josef

    Josef New Member

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    Well you'll always make some kind of wave but it won't really be the same as the bow wave made by a boat in displacement mode.
     
  17. KdaP

    KdaP New Member

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    bigger bigger bigger :D
    i know im exaggerating a bit, but what stops you from having a sail the size of a yacht and some racks the size of well, something big...

    kp
     
  18. phosphor

    phosphor Member

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    The strength of the materials, and the feasibility. After a certain point it's not practical.
     
  19. MasterMike

    MasterMike D22

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  20. phosphor

    phosphor Member

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    There is a dude who hit 48. something knots on a stinkin' windsurfer. He's a big guy with a lot of sail on a windy day.
     

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