Brits having a hard time in AC?

[wully1]

How do you know what proportion of time they spend on the foils. Anyway, it's not as simple as that. The bigger the foils and the more lift they create, the more drag they create also. So big foils with a high lift profile will get the boat foiling sooner but will have a slower top speed, whereas smaller, thinner foils will allow a higher top speed but will not create as much lift. So the whole "ground effect" hull shape really does matter, as this can create lift without the associated drag. Don't forget that the first iteration of the boat (and the American boat) were basically very flat underneath, and I suspect that they found the hulls very "sticky" (i.e. it took a lot of power to get the hulls to break clear of the water), which is why they have all shaped the hulls with things that look like steps (they are basically steps which reduce the wetted area, and hence the drag, quickly in stages as the boat begins to foil). This is a horribly complicated subject.

My worry is that it all comes crashing down because if there isn't enough wind for these boats to foil, the entire event becomes a failure.

The foil design has to be optimised - I never mentioned increasing size. These boats are supposed to be foiling so the proportion of time on foils is or should be 100%.

Also dropping off the foils at the speed these boat go at means your race is lost by a leg or so.

Also you cannot create lift without drag.

And...a flat hull surface has less surface area than a concave and so less skin friction drag. But..conclaves give more surface area. It’s tricky to get the balance of that and the requirement below.

And....to get planing you need a ‘planing flat’ don’t know what the yottie term is for that but curvy plan form hulls don’t plane.

All the stuff you talk about as been tried and tested before in surfing and windsurfing - guess what works? I’ll give you a clue - it’s not the clunky extreme shapes like Ineos.

 

[Bobc]

The foil design has to be optimised - I never mentioned increasing size. These boats are supposed to be foiling so the proportion of time on foils is or should be 100%.

Also dropping off the foils at the speed these boat go at means your race is lost by a leg or so.

Also you cannot create lift without drag.

And...a flat hull surface has less surface area than a concave and so less skin friction drag. But..conclaves give more surface area. It’s tricky to get the balance of that and the requirement below.

And....to get planing you need a ‘planing flat’ don’t know what the yottie term is for that but curvy plan form hulls don’t plane.

All the stuff you talk about as been tried and tested before in surfing and windsurfing - guess what works? I’ll give you a clue - it’s not the clunky extreme shapes like Ineos.

Optimised - how? As stated, there is a balance between lift and speed. Ineos currently lacks both.

You are correct that you cannot create lift without drag, but there's hydrodynamic drag and aerodynamic drag. If you optimise the hull for ground effect lift, you are gaining this without compromising top speed through the foils.

Planing? These boats don't plane. The reason for the hull steps is that a small amount of foil lift can reduce the wetted area, reducing drag and allowing a higher displacement speed, thus allowing the foil to create more lift and so on. With a simple flat hull, once you are in the water, you need to create a huge amount of power and lift to get it out again.

 

[wully1]

If I knew how to optimise their foils I’d be eating The Ineos designers lunch..... but he’s being paid a shed load of money for not much it would seem.

 

[TernVI]

What are the rules restricting the foils?
An aircraft wing has adjustable bits to vary its optimisation between takeoff, landing and flight,
Are these boats using one piece foils?

Is there a danger that the boat which is optimised to the conditions which actually happen will generally beat a boat better optimised for more or less wind?

 

[Whippersnapper]

Watching the AC mega yachts doing 4-5 knots in 10 knots of wind in the last race made me wonder if any previous AC race could have been won by a club racing dinghy.

They were never in 10 knots of wind. the Christmas race started in about 7knots and was down to about 6 near the end. Do t worry there is normally much more than 6knots of wind during an Auckland summer

 

[savageseadog]

I would imagine that the transitions between displacement/planing and foiling is absolutely critical, it would be easy to nose dive or climb if the transition wasn't perfect and as ever the more the foils are used to control the boat the greater the drag. I could only see the boat being developed as a complete package.

 

[Bobc]

They were never in 10 knots of wind. the Christmas race started in about 7knots and was down to about 6 near the end. Do t worry there is normally much more than 6knots of wind during an Auckland summer

I am led to believe that the predominant wind strength between January and March is less than 10kts.

 

[Bobc]

What are the rules restricting the foils?
An aircraft wing has adjustable bits to vary its optimisation between takeoff, landing and flight,
Are these boats using one piece foils?

Is there a danger that the boat which is optimised to the conditions which actually happen will generally beat a boat better optimised for more or less wind?

Quite. Air liner wings can transition between turbulent flow and laminar flow by shortening the chord length. Unfortunately there isn't the space if power to fit such mechanisms into an AC75 foil. They basically have to rely on the NACA profile to product lift and some trim tabs to adjust ride height.

 

[Ravi]

a balance between lift and speed. Ineos currently lacks both.

Not true. The fastest speed clocked was INEOS at 49 knots.

A donkey. But a donkey with the occasional kick.

 

[Ravi]

INEOS up for sale ..

America's Cup 2021: INEOS Team UK's Britannia II boat jokingly listed on TradeMe - NZ Herald

 

[Bobc]

Not true. The fastest speed clocked was INEOS at 49 knots.

A donkey. But a donkey with the occasional kick.

During the racing (on the breezier day), they were consistently 1-2kts slower than the other teams. Ben even said so in the post-race interview.

 

[Ravi]

During the racing (on the breezier day), they were consistently 1-2kts slower than the other teams. Ben even said so in the post-race interview.

Yes, but my point is that INEOS still clocked the fastest TOP speed of all the boats over the 3 day race series (despite being an all round embarrassment in every other respect).

So, the boat is not 'slow' given the right conditions. It went at a TOP SPEED of 49 knots.

INEOS can go fast. It may only go fast between 11:00 and 11:15 on a Friday when there is an R in the month but it CAN go fast. The trick for the designers and crew is to achieve those speeds under a wider range of conditions.

 

[Buck Turgidson]

Quite. Air liner wings can transition between turbulent flow and laminar flow by shortening the chord length. Unfortunately there isn't the space if power to fit such mechanisms into an AC75 foil. They basically have to rely on the NACA profile to product lift and some trim tabs to adjust ride height.

I like your posts and consider you a very knowledgeable sailor. Aerodynamics however isn't your strong suit.

 

[Bobc]

I like your posts and consider you a very knowledgeable sailor. Aerodynamics however isn't your strong suit.

You may well be right. My bible is the Ladybird book of aeroplane design ;-)

 

[TernVI]

Yes, but my point is that INEOS still clocked the fastest TOP speed of all the boats over the 3 day race series (despite being an all round embarrassment in every other respect).

So, the boat is not 'slow' given the right conditions. It went at a TOP SPEED of 49 knots.

INEOS can go fast. It may only go fast between 11:00 and 11:15 on a Friday when there is an R in the month but it CAN go fast. The trick for the designers and crew is to achieve those speeds under a wider range of conditions.

Top speed is rarely what you're looking for while racing. You're generally looking for vmg towards the next mark.
It would be interesting to see what speeds the boats could clock if they were doing a record attempt style 'mile in any direction'.

 

[LONG_KEELER]

INEOS up for sale ..

America's Cup 2021: INEOS Team UK's Britannia II boat jokingly listed on TradeMe - NZ Herald

Nice one .

Sport can certainly make you look stupid sometimes. You are only as good as you are today rather than yesterday. Thank god some keep trying anyway.

I remember about 20 years ago the England cricket team couldn't win a thing. It just happened that the team was not particularly talented at that time and others were, notably the Australians. The press still gave them a hammering though after every game though . Trouble is, things always come around again .

Zen master says, " When you judge, you do not define them, you define yourself".

 

[matt1]

Worth a watch re Ineos

 

[siwhi]

Worth a watch re Ineos

Interesting comments about boat pitch to take off. I thought while watching the racing that Ineos struggled to point as high (or as low 'downwind'), and therefore obviously had even lower VMG (ie compounding the lower SOG). They lost grip on the rudder more than once as well. Of course there is an interplay of factors, but the rudder could be important here to generate both the right pitch to facilitate initial foiling, and also lift to windward (akin to yaw) to work with the foils to crab / ferry glide upwind. What did he mean in the video when he says AM has 'negative leeway' and a less tightly sheeted main - does that mean lift to windward generated because the foil is in the water at a off-vertical or more flared angle in the water thus pushing the boat upwind, to some extent independently of heading?

 

[Bobc]

So what these guys are suggesting from what I can gather is that the other boats have some way of twisting the entire canting arms which changes the angle of attack of the foil, in order to help get the boat out of the water, and that the Ineos boat currently lacks this. If that is the case, then one would assume the problem can be resolved, but will need some significant engineering around the cant system mounts and the hydraulic systems.

 

[JumbleDuck]

As a matter of interest, how are the foils moved around? Are they allowed an engine (or a battery) to power hydraulics or does everything have to be operated by human power?