| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
17 Apr 2004 10:22:24 AM |
| Object: |
??? about wave action on inland lake |
Hi,
I have a boat on Lake Lanier in GA. The other morning I took it out,
and the overall wave action appeared to be different than usual.
It was a flat calm day, except when a passing boat produced some
waves. Most of the time the waves seem to be sort of peaked and
a bit sharp, but on this morning they were more rounded and flatter.
The first boat I noticed it from, I thought it might be simply due to
the shape of the boat itself. But after a while I noticed it was true of
all of them...which was cool with me because it meant I could go
faster without getting tossed in the air too much. It still made me
wonder *why* though. Could it have something to do with what
creates high and low tides, and/or why sometimes when you dig
a hole you seem to have more dirt than you took out and sometimes
you seem to have less? If so, is there a way to predict when waves
will tend to be sharper and when they will tend to be flatter, like
people can predict high and low tides?
.
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| User: "Androcles" |
|
| Title: Re: ??? about wave action on inland lake |
17 Apr 2004 11:20:50 AM |
|
|
<dh_ld@nomail.com> wrote in message
news:rsi280t88f22q34p7aulmob9raqhtu8bl9@4ax.com...
| Hi,
|
| I have a boat on Lake Lanier in GA. The other morning I
took it out,
| and the overall wave action appeared to be different than
usual.
| It was a flat calm day, except when a passing boat
produced some
| waves. Most of the time the waves seem to be sort of
peaked and
| a bit sharp, but on this morning they were more rounded
and flatter.
| The first boat I noticed it from, I thought it might be
simply due to
| the shape of the boat itself. But after a while I noticed
it was true of
| all of them...which was cool with me because it meant I
could go
| faster without getting tossed in the air too much. It
still made me
| wonder *why* though. Could it have something to do with
what
| creates high and low tides, and/or why sometimes when you
dig
| a hole you seem to have more dirt than you took out and
sometimes
| you seem to have less? If so, is there a way to predict
when waves
| will tend to be sharper and when they will tend to be
flatter, like
| people can predict high and low tides?
Possible causes are change in depth of water, change in
viscosity and oil slick. Alert the EPA.
Androcles
.
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|
|
|
| User: "zigoteau" |
|
| Title: Re: ??? about wave action on inland lake |
18 Apr 2004 08:59:31 AM |
|
|
wrote in message news:<rsi280t88f22q34p7aulmob9raqhtu8bl9@4ax.com>...
Hi, Dave,
I have a boat on Lake Lanier in GA. The other morning I took it out,
and the overall wave action appeared to be different than usual.
It was a flat calm day, except when a passing boat produced some
waves. Most of the time the waves seem to be sort of peaked and
a bit sharp, but on this morning they were more rounded and flatter.
The first boat I noticed it from, I thought it might be simply due to
the shape of the boat itself. But after a while I noticed it was true of
all of them...which was cool with me because it meant I could go
faster without getting tossed in the air too much. It still made me
wonder *why* though. Could it have something to do with what
creates high and low tides, and/or why sometimes when you dig
a hole you seem to have more dirt than you took out and sometimes
you seem to have less? If so, is there a way to predict when waves
will tend to be sharper and when they will tend to be flatter, like
people can predict high and low tides?
The following may not be the explanation of what you are seeing, but
could be worth bearing in mind:
Monolayers of surface-active materials can significantly dampen out
waves, and they're essentially not observable otherwise. It's related
to the old saw about pouring oil on troubled waters. This was known in
Antiquity (there is a reference in the works of Gaius Plinius
Secundus, Pliny the Elder, in AD 77). "Oil" in this context is not
mineral oil, which is essentially all hydrocarbons, but vegetable oil,
which is largely unsaturated long-chain fatty acids. A little oil goes
a long, long way, as found by Benjamin Franklin. In his letter to
William Brownrigg dated Nov. 7, 1773, he recounts that a teaspoonful
of oil calmed an area of about half an acre.
I was put onto this by a lecture I heard some years ago about a guy
responsible for a sewage-treatment pond. Suddenly, the sewage wasn't
breaking down as fast as it used to, and this was creating problems.
He tracked it down to a surface monolayer which was slowing down the
diffusion of oxygen. He had photos showing a very clear demarcation in
the wind-induced roughness of areas covered by monolayer and areas
which were clear. While I haven't ever had the equipment to go into
this scientifically, I've since often noticed vast differences in the
choppiness of a water surface when the wind is blowing, with a very
clear demarcation between them, and I think this must be due to
monolayer coverage.
The lecturer eventually got access to analytical equipment sensitive
enough to identify the material in his monolayer. He was expecting it
to be biological in nature, but it turned out to be oxidized motor oil
which someone had disposed of by pouring down the toilet.
Cheers,
Zigoteau.
.
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| User: "N:dlzc D:aol T:com \dlzc\ N: dlzc1 D:cox" |
|
| Title: Re: ??? about wave action on inland lake |
17 Apr 2004 01:06:13 PM |
|
|
Dear dh_ld:
<dh_ld@nomail.com> wrote in message
news:rsi280t88f22q34p7aulmob9raqhtu8bl9@4ax.com...
Hi,
I have a boat on Lake Lanier in GA. The other morning I took it out,
and the overall wave action appeared to be different than usual.
It was a flat calm day, except when a passing boat produced some
waves. Most of the time the waves seem to be sort of peaked and
a bit sharp, but on this morning they were more rounded and flatter.
The first boat I noticed it from, I thought it might be simply due to
the shape of the boat itself. But after a while I noticed it was true of
all of them...which was cool with me because it meant I could go
faster without getting tossed in the air too much. It still made me
wonder *why* though. Could it have something to do with what
creates high and low tides, and/or why sometimes when you dig
a hole you seem to have more dirt than you took out and sometimes
you seem to have less? If so, is there a way to predict when waves
will tend to be sharper and when they will tend to be flatter, like
people can predict high and low tides?
Wave speed is a function of water depth. Wave shape is a function of
dispersion (how far away the source is, temperature of the water), wave
speed vs. "boat" speed, and what is happening in the air.
I'd say the boats were just moving slower, which would not require as much
"cresting".
David A. Smith
.
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