[Public-List] (no subject)

[Bill Wallace]

I'm not sure where the Bay is, but that sort of sounds like something big/heavy fell into the water some distance away - something big like the side of a cliff or a large boat launching if it was far enough away that you didn't see/notice the cause.  It wouldn't likely be a microburst because waves take a fairly long time to develop from wind alone (you can compute how hard a burst it would need to be from the wind/fetch/time curves - but I would guess that nothing short of a tornado would generate the viewed waves).  It seems unlikely to be a boat wake if there were 10 of them - it would have to be a very large boat travelling quite slowly (say 10 kts for a tanker) to get that many waves - you can use the hull speed formula to calculate the distance required to get waves at a given velocity - say at 6 knots, roughly 30' for each additional wave beyond the first, so 10 waves would require 9*30 = 270' of boat length roughly.

Bill



----- Original Message ----
From: Dave Terrell <Dterrell at message.nmc.edu>
To: public-list at alberg30.org
Sent: Friday, September 18, 2009 9:35:01 AM
Subject: [Public-List] (no subject)

Earlier this summer while I was sailing Grand Traverse Bay in winds of 2 to 4 kts apparent with calm flat water and no power boats in the area, there suddenly appeared about about ten wave crests - one was a breaking wave - I thiink some of them might have been two feet high. The water around these waves was flat like all the rest of the water on the bay. When they passed - having  bumped me around  pretty well - the sea remained flat and the winds remained at the same speeds for most of the rest of the afternoon. The wave crests went all the way across the bay. I saw an other sail boat get knocked around as I was. The whole event lasted about two minutes - maybe a little more or less.

Any thoughts on what this event was? no reported midwest earthquakes or tremors that I know of tha day. The waves did not resemble the wake of a large power boat. To be sure I looked carefully and found none. Later a large power boat passed by and its wake did not resemble what I experienced in any way.

really curious. I have never seen this sort of thing before.

David, 432
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