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    Re: DR thread from Nov-Dec '04
    From: Trevor Kenchington
    Date: 2005 Jan 23, 14:32 -0400

    It certainly sounds as though you had reflected waves running across the
    ones running downwind. Shoal water and a windward-going current may have
    added to steepness of the waves but the short crests (measured along the
    line of the crest -- I think it is technically "narrow", not "short")
    sure suggests a second wave train crossing the main one and, at the
    southern end of the lake after a period of steady winds, reflection is
    the only explanation I can come up with.
    I'm surprised that enough energy would reflect off a shelving sand beach
    but there are plenty of surprises left in the ocean (for me at least)
    and no doubt more then enough in the Great Lakes too.
    Which should be a warning against trying to speculate about conditions
    that I didn't see on a lake that I have never sailed and have only the
    once seen from the shore. But, to ignore that warning ...
    You wrote:
    > Perhaps a problem with word usage.  I think of swells as a long series of
    > nicely formed "wave forms" 100 or more yards in length (across the crest).
    > Picture perfect.  Next would come "waves" which may come in a shorter series
    > but are maybe 75 ft or more wide, a bit choppy.  Some may be "squares", a
    > wall of water.  Mashed potatoes are a form confused sea. Piles of water,
    > perhaps the shape of pile of sand, 10'-12' high in this case .  (I say
    > perhaps as I could only view one side).
    As you probably know, technically "swell" is wind waves that have
    travelled out of the area where the wind built them. They do become much
    more regular with longer/wider crests, and with more even periods, as
    they move away from the wind which made them.
    What you are calling "waves" should likely be "seas" -- wind waves that
    are still being built, or at least maintained, by the wind. More
    irregular shapes, shorter/narrow crests, a wide variety of periods all
    Your "mashed potatoes" are most probably the result of two wave trains
    passing through one another at a rather wide angle, producing a "pile of
    water" where two crests coincide.
    You might, however, encounter something similar in a tide race, where
    the water can move vertically in a chaotic manner. I doubt that the
    currents in the lake would be fast enough to do that in anything but
    very shallow water but I may be wrong.
    > Now that you mention it, wind from the north would want to run parallel to
    > the lake's western shoreline.  If it were a billiard ball hitting the
    > Chicago coastline (rail) it would indeed head almost directly toward
    > Michigan City.
    > If it were a set up, then the water would continue to pile up on the
    > southern end as the wind velocity increased, right?  In this case, could it
    > have, like water in a creek that piles up to the outside of a bend, been
    > redirected as a southeast current (rather than the northeast current you
    > mentioned)?
    A north wind (meaning blowing from 360 exactly) ought to set up the
    water highest just about at Gary, that being the southernmost tip of the
    lake. I don't know whether or not some water water would downwell and
    flow back north as a near-bottom counter-current. I doubt that any would
    flow up the western shore of the lake, since that would be straight into
    the teeth of the wind. What I was suggesting before was that a flow
    might develop, following the shore from Gary past Michigan City, which
    would be about ENE.
    To flow SE, the water would have to be moving up the slope of the set-up
    (as it will while the set-up builds) but deflected to the left of the
    wind (i.e. contrary to the effects of Coriolis force). What might drive
    it that way? A wind somewhat east of north might have built the set-up
    more along the Chicago waterfront than centred on Gary. A windshift to a
    bit west of north could then readily slide water along the contours of
    the set-up, without having to fight gravity. There's probably a number
    of other explanations, dealing with the shape of the shoreline,
    underwater contours, inflow of less-dense waters from various rivers and
    whatever else. So a local, SE flow is always possible.
    Still, to get a marked effect on the waves, I'd expect a fairly intense
    current, which is more what I would expect from gravity pulling the
    set-up down as a narrow jet, rather than wind blowing over a wide area
    to pile the water up.
    Besides, if waves from the north are steepened by a current, that
    current must have some north in it. As SE wind would smooth out seas
    from the north, not steepen them.
    > All I can say for sure is that a 34' Catalina is usually pretty dull
    > compared to my Hobie 16 in the mid-20 kt breezes, but that day day was pure
    > fun!
    Never sailed a Hobie but the A-Class Unicorn cat I used to race when I
    was younger, and arguably more foolish, wasn't so much pure fun as pure
    terror when the weather breezed up past Beaufort 5.
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

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