Boats and foils comparison

Sidecar

…………………………
3,700
2,010
Tasmania
What is your hunch so far about the ideal AC75 foil area size if you can target, gamble on, lighter winds in October - as what Mozzy suggests ETNZ may be gambling on? Too early?
Foil area needed depends on how efficient the foil sections are, (ie how variable can you make CoL) and how much drag can be reduced from foil tips, flap tips, flap controllers, nose spine intersection, etc.

The more flap area, the better the chance of better CoL variation and control. The cleaner and smaller/fewer the flap ends and foil ends the better the drag reduction.

I don’t know the rules, but if allowed, I would be developing two sets of foils, max efficiency, min drag, of different areas and optimised sections, then decide at the last possible moment which set to use for the anticipated weather. And it looks exactly like what many of the teams seem to be doing.

It’s beyond my pay grade to make any main foil area predictions, I barely understand the physics as it is, and it depends on so many details…. and don’t forget the rudder……
 

enigmatically2

Super Anarchist
5,206
2,695
Earth
And for clarity, they cannot make 2 sets of foils and decide at the last moment. As soon as one set get wet, they are it. Though modifications are allowed within rule
 

shebeen

Super Anarchist
What is your hunch so far about the ideal AC75 foil area size if you can target, gamble on, lighter winds in October - as what Mozzy suggests ETNZ may be gambling on? Too early?
This is one of the big sneaks in the rules. By limiting all boats to just one foil design for both challenge series and match, Ineos as the CoR potentially handed ETNZ a huge advantage.

I really don't see the point to this restriction. By making all boats stick to a compromise jack of trades foil or gamble on a certain configuration we won't see the boats in their optimal package. 2 sets that can be changed daily would work just fine and probably not add that much additional cost.
 

JALhazmat

Super Anarchist
5,054
1,933
Southampton
likely, at the point that the foils were decided, it wasn’t intended to be racing in Barcelona with its slightly mental weather patterns and sea state.

certainly when the boats were conceived that Sea state definitely wasn’t part of the planning
 

Sidecar

…………………………
3,700
2,010
Tasmania
Here are some things to play with for the number crunchers:


You can change the equation to suit any variable you want.


Spend as much time as you like going through the library, but after a quick look, the one above gives some numbers which roughly relate to what I posted earlier. CoL is pretty much a linear increase from 0 degrees to 10 degrees AoA for most foils, so what you want is the foil with the highest CoL/CoD ratio at the highest AoA you can find/design.

Have at it!
 

Sidecar

…………………………
3,700
2,010
Tasmania
^^^^ And then there is the “climate change” trend which has affected weather records everywhere…. Certainly, down here, the weather has been abnormal (again) for this time of year…..
 

robingimblett

Member
61
78
Here are some things to play with for the number crunchers:

.......... CoL is pretty much a linear increase from 0 degrees to 10 degrees AoA for most foils, so what you want is the foil with the highest CoL/CoD ratio at the highest AoA you can find/design.

Ta, will have a read. This page https://web.mit.edu/2.972/www/reports/hydrofoil/hydrofoil.html
has a nice concise summary of hydrofoil physics which I found interesting, maybe you will also. The optimum AoA is around 3-4 degrees for hydrofoils for good lift / drag ratio.

Based on how they use the foils and foil arms through various manoeuvres, they appear to be lift neutral until the flap is engaged. I say that because the ride height of the boats rarely changes when the second foil drops in, and if the windward foil were to provide lift in that moment it would drastically alter the centre of lift position and also drastically reduce the righting moment.

It would be great to get some high res photos of a windward foil as it's dropping into the water to see if negative flap is applied.
 

Sidecar

…………………………
3,700
2,010
Tasmania
The optimum AoA is around 3-4 degrees for hydrofoils for good lift / drag ratio.
If you wade through the section library link, you can see that most of the foils in there have best lift to drag ratio at around 3-4 degrees.

In your linked article, lift to drag ratios of 20 to 25:1 are mentioned. Most of the sections in the library link have lift/drag ratios >80 even up to ~ 120. No mention of CoL’s either, but at 3-4 degrees AoA, they would be barely half of most foils’ maximums.

if you halved the CoL to 0.7 instead of the 1.4 upthread, the lift off speed goes up to 21 knots for a lift of 7700 kg?

And we are talking about whole foil AoA‘s and CoL’s, not flapped ones, which can’t be as efficient?
 

robingimblett

Member
61
78
@Kiwing sorry, no areas yet. But I've tried to create a bit of a template so images are more aligned with one another and includes the rule box for context.
Mozzy. The rule box overlaid is the AC75 size foil isn't it? Is there an AC40 foil dimension box we could use to compare actual size of ETNZ, AM & RB AC40 foils. Appreciate LR and INEOS LEQ12s may not have the same scale / mass as the other boats.
 

enigmatically2

Super Anarchist
5,206
2,695
Earth
As soon as anyone puts a new LEQ23 foil on an a Ac40 it doesn't have to confirm to AC40 rules either so could be bigger (or smaller if they think that tests at scale better/
 

enigmatically2

Super Anarchist
5,206
2,695
Earth
I get what you mean about the testing with and without tubucles as a single foil, but ita very hard to eliminate the effects of the different sides to work out which is best.
And they could have just done it as a modification, because that is a small fraction of the foil area changing
 

Sidecar

…………………………
3,700
2,010
Tasmania
Was discussing tubercules over in the ‘89er sports boat thread, and it came to me that perhaps they are also looking at reducing span flow on their main foils, which have easily the most sweep of any of the foils in this round of iterations. A bit like the row of riblets you see topside on most jet wings these days?

Also wondering how much flexibility they are building into the foils, especially the tips, so that they auto-flex to more feathering positions/shapes at high speeds/loads, making them less critical to stalling out? Again, a big sweep might help?
 

shebeen

Super Anarchist
Re the weather. Dont know about anyone else but I've observed the more important the regatta, the more "its never usually like this" happens.
ETNZ has "Clouds" heading up their weather team, right?
He's been top of the pile for years, for good reason.

As a casual weather "enthusiast", I have no reason to think he is not the best person for the job. I'm sure with all the years of experience he has assembled the best knowledge, the best people and the best tools.

Except this is his website, surely he is just trolling by not updating it?
 

I ride bikes

Member
205
129
Auckland
ETNZ has "Clouds" heading up their weather team, right?
He's been top of the pile for years, for good reason.

As a casual weather "enthusiast", I have no reason to think he is not the best person for the job. I'm sure with all the years of experience he has assembled the best knowledge, the best people and the best tools.

Except this is his website, surely he is just trolling by not updating it?
Who they really need, is Ken Ring.
Wind is created by waves don't you know 🙃
 



Latest posts

SA Podcast

Sailing Anarchy Podcast with Scot Tempesta

Sponsored By:

Top