Magic Number for Boats = 61.8?

Discussion in 'Boat Design' started by Capt Ronrico, Jun 27, 2018.

  1. DCockey
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    DCockey Senior Member

    Where did time come from?

    A separate "bow wake" does not exist. You can take an arbitrary portion of the bow and talk about the disturbance it generates. That disturbance interacts to a greater or less extent with the flow around the entire hull.
    My guess is you have a different understanding of how the wake of boat is generated and how it behaves than I do.
  2. JosephT
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    JosephT Senior Member

    Oh it's all in the timing & turn radius DC ;)


    Love posts like this. I have not heard of 61.8 degrees anywhere...suspect it may be a typo or perhaps the author was drinking. About 19 degrees seems to be what most references indicate in this fine year of 2018.

    Ship Kelvin Wake - WikiWaves
  3. Ad Hoc
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    Ad Hoc Naval Architect

    It doesn't per se.

    As DC has pointed out several times in this thread already. The main influence is water depth, as noted here, and it falls into 3 categories.

  4. Capt Ronrico
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    Capt Ronrico Junior Member

    Oops. I dug out my copy of Craven - it was in storage - and he actually said: "The wedge containing the bow waves invariably makes a perfect 19 degree 28 minute angle with the path of the ship. Similarly, the bow waves diverge tangent to a line that is always 35 degrees 16 minutes with the path of the ship." I don't know how I managed to transmogrify this into 61.8; raw talent I guess.
    That said, is there an entry angle that mandates an energy spike as you approach, equal, and exceed it? And if so, what is it?
    Also, David Ritchie asked about Thresher and Scorpion. Large topics. Thresher failed due to engineering problems, apparently. Scorpion's demise is a little murkier. One theme blames it on its own torpedo - there are several variants on this theme. Another theme blames it on the Soviet navy, which was carrying out fleet exercises in the area at the time. The Sov's had just lost K-129 and may have blamed the U.S.
    It was a bad year for submarines worldwide: 4 were lost: 1 each for the US, USSR, France and Israel.
  5. DCockey
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    DCockey Senior Member

    No angle which results in an abrupt increase in drag. The 19 degree 28 minute angle occurs at a distance behind the vessel, not directly adjacent to the vessel.
  6. gonzo
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    gonzo Senior Member

    I don't understand what you mean by the bow wake being time delayed or how can that happen. Is it that the hull moves through the water and the wave is generated later? Wakes are generated by the complete hull. For example, ski and wakeboats use trim and ballast adjustments to modify the size, shape and angle of their wake.
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm pretty sure the angle of these wakes changes in direct proportion to the amount of rum consumed, but I don't have any data.

  8. messabout
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    messabout Senior Member

    Of some interest is the converging wave patterns of catamarans. I have seen claims that the distance between hulls should accommodate the 19 degree rule. That is to say that the distance between the hulls of a 25 foot cat ought to be something like 8.6 feet. I never quite bought into that claim because of the water depth factor.

    Watching cat wakes is an interesting pursuit. Two boats running parallel and close together produce the same interaction of waves. Competitive dinghy sailors are conscious of the phenomena.
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