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Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

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Stefano De Martini
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#11

Post by Stefano De Martini »

I believe that one of the determining factors is the density of the air. The denser this is, the more friction increases. For example in the indoor Tallinn World Cup the temperature is often close to 0 and believe me the line does not even run with dynamite. Mine is the longest throw of any event of all years and is 34.62m with the MED if I remember correctly. This is probably because the air is dense due to the low temperature and the humidity is high. Conversely casting at 2000m above sea level is much more effective due to the thin air.
Regarding the concept of the wind in favor that can facilitate the cast with a "sail" effect, I can only say that the flight speed of a MED line is very close if not higher than 100 km/h so even a good tailing wind of 15/20 km/h would have little influence in my opinion. Instead, since the friction increases proportionally with the speed, the tailing wind also in this case considerably reduces the friction during the flight because the relative speed respect to air is reduced.
Paul humid air is denser than dry air. So in my opinion the answer to your question is in what I have tried to expose above...
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Paul Arden
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#12

Post by Paul Arden »

Hi Stefano, that’s actually the issue because humid air is less dense than dry air. There is a good explanation as to why this is so, about half way through this page. https://iflycoast.com/understanding-air ... s-effects/

I know! It’s surprising because the results in fly casting would indicate the complete opposite. However in golf I believe the results are consistent with humid air being less dense. Maybe Phil can add something to this topic?

Cheers, Paul
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Dirk le Roux
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#13

Post by Dirk le Roux »

Stefano De Martini wrote: Tue May 11, 2021 8:02 am Paul humid air is denser than dry air. So in my opinion the answer to your question is in what I have tried to expose above...
Hi Stefano

Humid air is less dense than dry air.

Cheers,
Dirk
Stefano De Martini
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#14

Post by Stefano De Martini »

My apologize, you are right and it seems that I am totally ignorant in physics.
I apologize but it seemed as obvious to me as when adding salt to water. Honestly i didn't checked before. :D
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#15

Post by Dirk le Roux »

No prob, Bob

It certainty is counter intuitive. I only learned that the hard way (years ago) landing hang gliders at altitude on hot and humid days, in zero wind!
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#16

Post by Paul Arden »

It would be the natural assumption, Stefano. I also believed if to be true until only a few years ago and you would certainly think it to be the case if you were casting in the tropics. But the opposite is true. Consequently I should be throwing my longest casts here in Malaysia, but anything over 120’ and angels start singing.
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Richard Floggwater
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#17

Post by Richard Floggwater »

A point Paul made - explain dew point and fog. I still can’t explain the cast/kill effect.

From the National Atmospheric and Oceanagraphic Administration in the US

Dew Point vs. Humidity
The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold more water in the gas form. If the air were to be cooled even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.

The higher the dew point rises, the greater the amount of moisture in the air. This directly affects how "comfortable" it will feel outside. Many times, relative humidity can be misleading. For example, a temperature of 30 and a dew point of 30 will give you a relative humidity of 100%, but a temperature of 80 and a dew point of 60 produces a relative humidity of 50%. It would feel much more "humid" on the 80 degree day with 50% relative humidity than on the 30 degree day with a 100% relative humidity. This is because of the higher dew point.

So if you want a real judge of just how "dry" or "humid" it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel.

General comfort levels USING DEW POINT that can be expected during the summer months:

less than or equal to 55: dry and comfortable
between 55 and 65: becoming "sticky" with muggy evenings
greater than or equal to 65: lots of moisture in the air, becoming oppressive

Fog -
Radiation Fog

This type of fog forms at night under clear skies with calm winds when heat absorbed by the earth’s surface during the day is radiated into space. As the earth’s surface continues to cool, provided a deep enough layer of moist air is present near the ground, the humidity will reach 100% and fog will form. Radiation fog varies in depth from 3 feet to about 1,000 feet and usually remains stationary. This type of fog can reduce visibility to near zero at times and make driving very hazardous.

Valley fog is a type of radiation fog. When air along ridgetops and the upper slopes of mountains begins to cool after sunset, the air becomes dense and heavy and begins to drain down into the valley floors below. As the air in the valley floor continues to cool due to radiational cooling, the air becomes saturated and fog forms. Valley fog can be very dense at times. This type of fog tends to dissipate very quickly once the sun comes up and starts to evaporate the fog layer.

Advection Fog - The type I’d think one would see at the Golden Gate Casting ponds

Advection fog often looks like radiation fog and is also the result of condensation. However, the condensation in this case is caused not by a reduction in surface temperature, but rather by the horizontal movement of warm moist air over a cold surface, such as warm moist air flowing over snow. Advection fog can sometimes be distinguished from radiation fog by its horizontal motion along the ground.
Richard Floggwater
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#18

Post by Richard Floggwater »

Apologies but I think I need to clarify a question point.

Please note that although I mentioned a sail effect in the question, I am really not a full proponent of the idea, but respect the people I know that suggested it. I believe something happens to relieve the drag on the loop with a downwind cast not seen on a calm distance cast situation. I believe that the loop’s turnover time is lengthened potentially by the rod leg having less drag traveling downwind, and this in turn delays the fly leg unrolling to the lines end allowing for a longer cast. On turnover a cast tends to really start falling, and although there may be some final forward motion the control a loop provides is at that time absent. This situation I think is very different from calm wind scenarios where I believe the turnover time is accelerated with stunted rod leg travel due to more drag compared to downwind situations. Downwind does not equal Calm distance casting.
Bianchetti Ivan
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#19

Post by Bianchetti Ivan »

I would not be wrong but I have the feeling that it centers the heat exchange of the ground, when the sun irradiates the earth and becomes hotter than the air, a kind of hot bubble forms, this could affect, the wind carries things therefore it probably also carries the line, of course I'm ignorant on the subject, that's why I have a feeling and not a certainty.
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Re: Distance Casting In Hot-Humid-Calm Conditions: Thin Air Tough Casting?

#20

Post by Stefano De Martini »

:D Ivan, you need to adjust some translation of Google. By the way because i'm italian i well undestand what you are meaning. Yes i agree. The hot air on a sunny summer day certainly tends to create a convective motion by "lifting" the line as well.
Certainly with the warm air that is less dense than the cold one and with a little push upwards there can be some advantages.
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