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Hydrofoil lift in different water temperature /salinity

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revhed
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Re: Hydrofoil lift in different water temperature /salinity

Postby revhed » Mon Dec 04, 2017 6:55 pm

tahoedirk wrote:
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.
For example, even just today.
There is a channel that feeds from a HUGE etang, pond into a smaller where we foil to try to avoid algae.
You could SEE clearly the BROWN, dirty H20 and dreded algae which was a challenge to cross flying EACH time!
As well fishing boats pass from time to time and even after you think the wake has calmed you can feel it, like MUCH later than you would think!
So I would think that as posted above MANY factors can and will affect your foils flying.
R H

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Re: Hydrofoil lift in different water temperature /salinity

Postby TomW » Mon Dec 04, 2017 8:23 pm

Yes, it is probably sediment I have been feeling. It feels like big difference in lift.

This weekend we had luck to get 2 sessions in 4c air and water. At times foil is jerking and veering around. I think I'm hitting individual strands of sea grass, small clumps of grass and small jellyfish I saw at waters edge. There's no fish, fished out and dead a long time ago.

In Brazil I never felt any of this, it was smooth and consistent always.

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Re: Hydrofoil lift in different water temperature /salinity

Postby cwood » Tue Dec 05, 2017 3:58 am

revhed wrote:
Mon Dec 04, 2017 6:55 pm
tahoedirk wrote:
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.
For example, even just today.
There is a channel that feeds from a HUGE etang, pond into a smaller where we foil to try to avoid algae.
You could SEE clearly the BROWN, dirty H20 and dreded algae which was a challenge to cross flying EACH time!
As well fishing boats pass from time to time and even after you think the wake has calmed you can feel it, like MUCH later than you would think!
So I would think that as posted above MANY factors can and will affect your foils flying.
R H
Always amazes me how long prop wash can be felt after a boat has passed.

juandesooka
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Re: Hydrofoil lift in different water temperature /salinity

Postby juandesooka » Tue Dec 05, 2017 4:46 am

It is a noticeable difference when surfing in a river mouth (cold water), when transition between the salt water and fresh water zones. Fresh water feels more sluggish, assumed from less salinity and also colder. This is especially noticed paddling, but also surfing. Probably same thing with foil, though maybe if moving fast enough it's only a minimal difference.

3InletsWindsports
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Re: Hydrofoil lift in different water temperature /salinity

Postby 3InletsWindsports » Tue Dec 05, 2017 11:24 am

Having gone from 6c water and 13c air temp to holiday with 22c water 28c Air.
Yes it is noticeable . Maybe 2 kts more board speed to takeoff which if takeoff is 10 knots makes it significant

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Re: Hydrofoil lift in different water temperature /salinity

Postby bohme » Tue Dec 05, 2017 11:47 am

The difference in viscosity is the most important parameter.
Warm fresh water viscosity can be 50% of cold saltwater. Reynolds number is linear with viscosity. This affect boundary layer, stall angle, drag, balance and maximum speed.
I use different wet sanding summer/winter.

cwood
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Re: Hydrofoil lift in different water temperature /salinity

Postby cwood » Tue Dec 05, 2017 11:58 am

I went from Cuba to Ontario sessions within 2 days a few weeks ago. I noticed very little on the wing difference in feel but touch downs are more forgiving on salt water due to buoyancy.

I can tell you I felt a drastic difference in kite feel in boosting between 28 C wind and 4 degree wind. I would wager about a 15% power difference, maybe more for an equivalent wind speed. Cold is just way more boosty. First send of the kite back home and I was shocked at the difference. Happy to live in cold climate as a boost obsessed person.

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Re: Hydrofoil lift in different water temperature /salinity

Postby borist » Tue Dec 05, 2017 7:08 pm

TomW wrote:
Mon Dec 04, 2017 8:23 pm
Yes, it is probably sediment I have been feeling. It feels like big difference in lift.

This weekend we had luck to get 2 sessions in 4c air and water. At times foil is jerking and veering around. I think I'm hitting individual strands of sea grass, small clumps of grass and small jellyfish I saw at waters edge. There's no fish, fished out and dead a long time ago.

In Brazil I never felt any of this, it was smooth and consistent always.
I get that during low tide when bottom growth get closer to the surface. Wings catch little bits of soft weed here and there causing sudden quick jerks or occasional "softer lift" or vibrations. Quite different from what eelgrass does

As for salt/fresh water, my experience is that I personally don't notice the difference. Take-off, speed and balance feels the same to me. Perhaps if you transition between the two quickly, but I always had at least a day between the sessions


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