# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: DR thread from Nov-Dec '04
From: Bill B
Date: 2005 Jan 19, 18:52 -0500

```Jared

Some observations come to mind:

I would agree with your dictionary definition of fetch, and duration in
partnership with fetch, but with the following caveats:

In the example you gave the fetch was from a wind blowing from Japan to
California.  If you are on the beach in California, the distance (4000
miles) is indeed the fetch.  If you are on a watercraft half way between,
then from the craft's perspective (which is what we are interested in for
calculating set and drift) the "fetch" is 2000 miles. In either case, I
would guess ample distance for the wind to affect surface currents.  On Lake
Michigan if the wind was out of the north or south, a greater fetch than out
of the east or west.

Also, the dictionary definition deals with waves, not wind-induced current.

Lastly, can we count on the wind direction and velocity being identical in
both Japan and California?  From the texts I have read wind-induced current
can be a relatively local event, e.g. Chesapeake Bay or Great Lakes.  On
Lake Michigan we get these wonders called seiches.  High pressure on one end
of the lake, low pressure on the other, plus the wind in the right direction
and bam, a foot or more "tide" over a matter of hours.  The first time we
experienced it was when tied up along the wall in Chicago.  Blew my mind.
Perhaps Frank can offer a better explanation of the seiche from the Chicago
vantage point.

All this raises the question, how "local" can the affect be?  I don't know.

I have no argument for or against the proper use of the word "fetch" in the
text I read, just the above observations.  If the author of the text misused
it, I am guilty only of propagating that error ;-)

Bill

> Bill-
> <>
>
> I've never seen it used that way. From my cheap dictionary:
> "4.a. The distance over which a wind blows. b. The distance traveled by
> waves with no obstruction."
>
> Which agrees with the way I've always heard it, i.e. a west wind, perhaps
> better called a easterly wind , blowing from Japan toward California
> unobstructed, from the California local sailors' perspective, would cause
> waves and current to build with a four thousand mile fetch. That is, the
> wind had been acting on the water for four thousand miles.
>
> The longer the wind has been blowing, and the longer the fetch is, the
> stronger the impact on the water will be.
>
> (Four thousand being a terribly rough number, don't use it for

```
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