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Hydrofoil lift in different water temperature /salinity

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TomW
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Hydrofoil lift in different water temperature /salinity

Postby TomW » Sat Dec 02, 2017 5:13 pm

With there be a noticeable difference in hydrofoil lift in water that is 4c vs 20c or ocean water and fresh water?
Or combination? for example 4c ocean water. Vs 24c fresh water.

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Re: Hydrofoil lift in different water temperature /salinity

Postby plummet » Sat Dec 02, 2017 6:13 pm

No.

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Peter_Frank
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Re: Hydrofoil lift in different water temperature /salinity

Postby Peter_Frank » Sat Dec 02, 2017 6:46 pm

The lift difference equals the density difference.

For water with 3.9 % salinity versus fresh water, the lift is about 3 % higher in the salty one.

If the temperature changes from 24 C to 4 C, the lift is only 0.3 % higher in the cold water.

So I doubt you can feel the difference, as it is only 3.3 % total :wink:

It would correspond to having a 700 cm2 wing and a 723 cm2 wing - can you feel the difference ? Some might, most cant I think.

On the other hand in some scenarioes it is more evident, when windsurfing on shortboards that only just floats, or maybe just sinks, I remember it was clear that it sank deeper in the fresh water, very noticeable even if just 3 % difference.

8) PF

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Re: Hydrofoil lift in different water temperature /salinity

Postby TomW » Sat Dec 02, 2017 9:22 pm

Thanks Peter. I couldn't do the math.
What I'm feeling must be turbulence or debris in the water.
I'm foiling near a river mouth, but the ocean isn't very salty.

I also felt that foiling in Brazil, there was more lift. The water is very salty there.

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Re: Hydrofoil lift in different water temperature /salinity

Postby baxterbradford » Sat Dec 02, 2017 9:30 pm

Isn't the sinker issue the difference between static and dynamic buoyancy Peter which is more affected by relative density of saline vs fresh water? Hydrofoil having virtually no buoyancy and producing almost all dynamic lift.

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Re: Hydrofoil lift in different water temperature /salinity

Postby kiterocky » Sat Dec 02, 2017 9:31 pm

Hahaah this post win..

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Re: Hydrofoil lift in different water temperature /salinity

Postby plummet » Sat Dec 02, 2017 9:39 pm

If you added air temp difference than maybe you have conditions that force the next size up kite.

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Peter_Frank
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Re: Hydrofoil lift in different water temperature /salinity

Postby Peter_Frank » Sat Dec 02, 2017 10:05 pm

baxterbradford wrote:
Sat Dec 02, 2017 9:30 pm
Isn't the sinker issue the difference between static and dynamic buoyancy Peter which is more affected by relative density of saline vs fresh water? Hydrofoil having virtually no buoyancy and producing almost all dynamic lift.

The sinker issue when uphauling, or at least when no speed, is the static buoyancy difference indeed so the relative density is the very difference, correct.

And a hydrofoil wing will lift proportional to the water density (given the same speed), meaning you have a tad more lift with the same size wing in salty water.
I have left out the hydrofoil buoyancy, it is neglectable.

So you are right, it is two different physical things, but they are affected with the same amount :thumb:

And plummet is spot on, the air temperature difference means somewhat more, as air can be compressed a lot more than water, so from 26 to 4 degree air temp you get 8 % more lift from the kite.
And in reality, in the given conditions from winter 4 degree water to somewhere with 26 c water, the air difference could easily be 30 degree, which means 11 % more pull from the kite, when cold.

8) PF

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Re: Hydrofoil lift in different water temperature /salinity

Postby tahoedirk » Mon Dec 04, 2017 5:32 pm

The answer to the first post is YES.

Huge difference !

Salt , debris, sediment ,temperature, and who knows what else, make an obvious difference in foil performance.

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Re: Hydrofoil lift in different water temperature /salinity

Postby Mossy 757 » Mon Dec 04, 2017 5:52 pm

I've ridden through tide lines that separated clear ocean water from silty brown bay water and felt an enormous difference crossing between the interface. On the clear side, it was very light and easy to ride. On the silty brown side I couldn't stay on foil or seem to power up properly, the foil would start to accelerate then just crash down without warning.

I'm still not sure what to make of this session, I've only seen it one time, but it was night and day.


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