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Sailing

SpurMeUp

SpurMeUp

Jimmy Cantrell
Been keeping an eye on the America's Cup. Mainly as the physics of these current foiling boats is fascinating. How does it work? How does a pressure difference lift many tonnes out the water? I know its the same as with planes but they baffle me too.

The UK boat has been shockingly bad in all the warm-up races. Our lads were beaten in every race and limped home hundreds of meters behind the faster, slicker US boat, Kiwi boat and even the Italians! But it is a race for development as much as a test of seafaring. It is the F1 of sailing. 50mph across the waves. When a crash happens it will be dramatic.

This is the first race to determine who will challenge the Kiwis - who currently hold the Cup. The British boat up first who are the underdogs vs the yanks:

 
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SpurMeUp said:
Hello Sailor! [emoji6]


Maybe someone can explain how these boats fly?

Sitting on my porcelain throne using glory-glory.co.uk mobile app
Click to expand...
They use hydrofoils don't they?

The top surface is longer than the bottom. As the water splits and runs around the hydrofoil, the water over the top edge has to travel faster than that under it. Liquids moving faster are at a lower pressure than those that are slower - that differential in pressure is what creates lift. Same as with an airplane wing.

It's over two decades since I studied this stuff but Euler's equations will tell you how much lift a certain shape and surface will create:
https://en.m.wikipedia.org/wiki/Euler_equations_(fluid_dynamics)
 
ricky2tricky4city said:
All my dingdonghead mates are foiling off East Head the last few months...Mrs reckons there must of been 30 in today.
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Wow. Don't fancy getting into a wetsuit? @Danishfurniturelover might hold his own (and others) in a wetsuit :) There is a tiny resovir where you can do some basic sailing training close to me, so might give it a go. I messed around sailing as a kid. Would love to try the small foiling dinghies. Must be a blast 'taking off' and riding above the waves.
 
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scaramanga said:
They use hydrofoils don't they?

The top surface is longer than the bottom. As the water splits and runs around the hydrofoil, the water over the top edge has to travel faster than that under it. Liquids moving faster are at a lower pressure than those that are slower - that differential in pressure is what creates lift. Same as with an airplane wing.

It's over two decades since I studied this stuff but Euler's equations will tell you how much lift a certain shape and surface will create:
https://en.m.wikipedia.org/wiki/Euler_equations_(fluid_dynamics)
Click to expand...

Yes! And they are propelled with the same physics at play, so I'm told. Rather than the sail catch the wind to push these boats along, its more of a wing creating pressure zones? In 10 knots of breeze they sail at 30 knots. Just amazing.

But I still don't really believe it. How can a pressure difference between each side of a tiny foil, lift the full weight of a 6-7 tonne boat? Witchcraft. Its one sport that has real innovation. F1 is pretty controlled and designers are impotent now. The range of weather variables ,and mix of aero, sail, foil tech, plus tactics, and racing means it's an interesting watch. Didn't even bother with F1 this year after the first few races. Predictable and lacking interest.

FWIW, Rita, the British boat made some upgrades, destroyed the yanks and beat the Italians on day 1. Day 2 highlights:


About to check out day 3, which was last night.
 
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SpurMeUp said:
Wow. Don't fancy getting into a wetsuit? @Danishfurniturelover might hold his own (and others) in a wetsuit :) There is a tiny resovir where you can do some basic sailing training close to me, so might give it a go. I messed around sailing as a kid. Would love to try the small foiling dinghies. Must be a blast 'taking off' and riding above the waves.
Click to expand...
They're doing wing foiling
upload_2021-1-17_11-4-37.png

I can't be arsed...more kit and the Mrs would moan. I'm in the sea as much as possible as it is.
They're putting foils on all kinds of watercraft these days. It lifts you above the friction of the water so everything is so much smoother.

Sailing is a lovely thing. I'm just competent crew to my two nephews who are bang into it. We go over to IOW at least 3 times a year.
 
SpurMeUp said:
Yes! And they are propelled with the same physics at play, so I'm told. Rather than the sail catch the wind to push these boats along, its more of a wing creating pressure zones? In 10 knots of breeze they sail at 30 knots. Just amazing.

But I still don't really believe it. How can a pressure difference between each side of a tiny foil, lift the full weight of a 6-7 tonne boat? Witchcraft. Its one sport that has real innovation. F1 is pretty controlled and designers are impotent now. The range of weather variables ,and mix of aero, sail, foil tech, plus tactics, and racing means it's an interesting watch. Didn't even bother with F1 this year after the first few races. Predictable and lacking interest.

FWIW, Rita, the British boat made some upgrades, destroyed the yanks and beat the Italians on day 1. Day 2 highlights:


About to check out day 3, which was last night.
Click to expand...
Ever used a kite surfing/boarding kite? It's the same again.

You can stand still and hold the kite whilst it's in the air, but make it move through the air and it'll lift you.

If the power to weight seems improbable, just think how much an aeroplane weighs. They obviously use power to move forwards, but their lift is generated the same way.
 
ricky2tricky4city said:
They're doing wing foiling
View attachment 10644

I can't be arsed...more kit and the Mrs would moan. I'm in the sea as much as possible as it is.
They're putting foils on all kinds of watercraft these days. It lifts you above the friction of the water so everything is so much smoother.

Sailing is a lovely thing. I'm just competent crew to my two nephews who are bang into it. We go over to IOW at least 3 times a year.
Click to expand...

While that looks incredible, can imagine being in the water more time than up. Also need to be able to surf or windfurf? Even foiling dinghies are probably a little too edgy for me! Guessing you spend your time trying to balance everything, with reduced friction and increased speed, its a bit of tightrope walk to keep everything balanced. A normal sailing boat would be my preference. Sounds like you're on it, the water around the IOW some of the busiest and full of currents etc. My family used to have a little sailing boat and beach hut in Dorset. Sadly it didn't get used enough.
 
Been catching up with the last few days. Great viewing and commentary for novices like myself on the americas cup site.

I have followed this before one of my distant Aussie kin was involved in boat design of Alan bonds Aussie team back in the day. Also followed that previous English America’s cup effort can’t remember his name now.

looking forward to the rest of this now.

^^Edit was it Peter de Savaray?
 
scaramanga said:
Ever used a kite surfing/boarding kite? It's the same again.

You can stand still and hold the kite whilst it's in the air, but make it move through the air and it'll lift you.

If the power to weight seems improbable, just think how much an aeroplane weighs. They obviously use power to move forwards, but their lift is generated the same way.
Click to expand...

Is it because water is so much denser than air, that a small foil can lift a huge boat?

Haven’t got my head around how the sail ‘wing’ works yet.


Sitting on my porcelain throne using glory-glory.co.uk mobile app
 
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