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shes legit ... foil arm looks to be in the front end of the box ... opposite of all other teams ... what are we going to read into that?

ETNZ are probably favorites .....but win or lose....Team New Zealand have firmly established themselves as the all time great AC nation in the modern era.   From the time they first emerged, they have

And so it begins. Image credit and copyright Allesandro Spiga  

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23 minutes ago, Chris UK said:

One is back to winning ways, taking the Tour of Italy earlier today. Well done Tao Geoghegan Hart!

Great young talent , humble too. Good win on final TT and apparently did not need a asthma TUE to do it unlike so many of the other Sky /Ineos Grand tour wins. Their car won today as well in a run-away. 

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For the record, flap rules (ver 1.10)

Quote

15 Foil flaps

15.1 A foil flap must be a linear component connected to a foil wing by a foil system.

15.2 Each foil shall include two foil flaps, one lying entirely on one side of the foil wing symmetry plane, and
one lying entirely on the other side of the foil wing symmetry plane.

15.3 For the purposes of Rule 15:

(a) a “cross-section” is defined locally at any spanwise location along the rondure of the foil wing as a
section through a foil wing and foil flap, on a plane perpendicular to the rondure at that spanwise
location; and

(b) the “chord length” at a given cross-section and a given foil flap rotation angle is the distance between
the most forward point and the most aft point on the cross-section, when projected on to the foil
wing projection plane shown in Figure 13.1.

15.4 At any cross-section, the only permitted movement of a foil flap relative to a foil wing is a rotation about
an axis that remains approximately stationary with respect to the foil wing at that cross-section. This axis
must be designed to be stationary, but is permitted to have some movement resulting from:

(a) play in a mechanical bearing; or

(b) a flexure or soft hinge, such as a thin flexible material joining the foil flap to the foil wing.

15.5 Through a foil flap’s range of rotation angles and twists, a foil flap cross-section shall not significantly
deform except as permitted in Rules 15.4, 15.8 and 15.9, or as a result of external forces.

15.6 Both foil flaps of a foil shall have the same range of angular rotation and twist. With both foil flaps of a
foil centred in their ranges of motion, each foil flap shall be symmetric with respect to the other about
the foil wing symmetry plane, with a build tolerance of 3.0 mm.

15.7 At any cross-section and all rotation angles, when projected on to the foil wing projection plane, the length
of a foil flap must not be greater than 50% of the chord length. Hinges or other parts of a component which
occur at occasional cross-sections for connection purposes can be excluded from the projected lengths.

15.8 A foil flap may contact a foil wing, and in the absence of external forces, and at any cross-section and
rotation angle, either may cause deformation in the other in a single zone covering not more than 20% of
the local chord length. Outside this zone, neither shall cause deformation in the other.

15.9 Connections between sections of a foil flap are exempt from Rules 13.9, 15.4 and 15.5, providing such
connections span a combined total of no more than 10% of the span of a foil wing, where the span is
measured along the rondure

At any cross-section there can be only one flap & operating on one axis.

But it envisages multiple sections connected flexibly & doesn't seem to require all sections to be on the same axis.

 

I thought we'd agreed back when B1 launches happened that at least a couple of the teams seemed to be using external hinges

a2820065-48-Flaps%2015.JPG

I'm not necessarily convinced its a fast solution but it seems to be what they're doing.

You can see its made of 2 parts in @mikenz2 pics.

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2 hours ago, mikenz2 said:

A couple of new photos for y'all:

 

 

@mikenz2.  Great photos thanks!  Have run them through Gigapixel AI as per usual to allow reasonable blur-free enlargement.  Link here: https://www.dropbox.com/sh/eh6esoolboxnl48/AAAIrh-p3IjPNjcJ1lgEaMMea?dl=0 .  I'll add to the folder if any more appear.

Cheers,

Geoff

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From Americas Cup 36 Facebook page. Found it interesting.

We followed both Britain and USA on the water today there was a good breeze but both needed to be pulled onto their foils by one of the tenders. Neither could get up without assistance. Does anyone know why?
Image may contain: ocean, sky, boat, outdoor, water and nature
 
 
 
 
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9 minutes ago, GeeJay said:

@mikenz2.  Great photos thanks!  Have run them through Gigapixel AI as per usual to allow reasonable blur-free enlargement.  Link here: https://www.dropbox.com/sh/eh6esoolboxnl48/AAAIrh-p3IjPNjcJ1lgEaMMea?dl=0 .  I'll add to the folder if any more appear.

Cheers,

Geoff

Thanks got my copy and these foils are getting  weirder and weirder

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27 minutes ago, Forourselves said:

From Americas Cup 36 Facebook page. Found it interesting.

We followed both Britain and USA on the water today there was a good breeze but both needed to be pulled onto their foils by one of the tenders. Neither could get up without assistance. Does anyone know why?
Image may contain: ocean, sky, boat, outdoor, water and nature
 
 
 
 

I watched INEOS jump into its foils unassisted yesterday, so I wouldn’t get too excited. 

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Very quiet northerly conditions today on the sparkling Waitemata Amway got away unassisted and fanged off towards Whangaparoa well north of course A into a better breeze whilst the Frackers buggered about for ages on course B and finally got underway taking it all very cautiously.

 

 

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4 hours ago, hoom said:

For the record, flap rules (ver 1.10)

At any cross-section there can be only one flap & operating on one axis.

But it envisages multiple sections connected flexibly & doesn't seem to require all sections to be on the same axis.

 

I thought we'd agreed back when B1 launches happened that at least a couple of the teams seemed to be using external hinges

a2820065-48-Flaps%2015.JPG

I'm not necessarily convinced its a fast solution but it seems to be what they're doing.

You can see its made of 2 parts in @mikenz2 pics.

Yes I think it is a hybrid so the inner flap is like this and the outer is a simple flap sharing a common axis of rotation. 

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This pic from @weta27 seems to confirm they're running a continuous jib track...? independent sheet control to get around the rule but perhaps marginally more clew/leech control through the tacks compared to split tracks?

And also if you look just forward and down from my yellow circle there's what appears to be a camera mounted on the side of the boat looking down at the foils..

RB2 jib.jpg

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23 minutes ago, NZK said:

This pic from @weta27 seems to confirm they're running a continuous jib track...? independent sheet control to get around the rule but perhaps marginally more clew/leech control through the tacks compared to split tracks?

And also if you look just forward and down from my yellow circle there's what appears to be a camera mounted on the side of the boat looking down at the foils..

RB2 jib.jpg

There's cameras at the top of the mast as well.

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Wow... The photos from @mikenz2  and then pimped up by @GeeJay show lots of interesting and confusing detail!
 

I've had a go at marking up, but... I just don't know. The photo of the top surface of the foil seems to show a number of 'hinge' lines, which one is real?

Could it be that the only actual hinge is '2'? It's the only one that has a continuous bright strip visible on the under-side. 

It's as if the leading edge section starts to bend down at '1'  (or hinge??) and its marked with a line of evenly space 'dimples'. From previous photos I assumed these were just low resolution effects on the actual hinge or flexible joint. But these enhanced and taken from closer distance photos seem to show that these are some flow conditioning/disturbing dimples...

Then at line '2', the inward part of the flap is hinged and is connected with a flexible patch marked '?'. Then line '2O' is not hinged and also has 'dimples' along it.

In any case, these foils don't seem agricultural to me...

Ineos-Foil_top-and-bottom.png

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3 hours ago, JALhazmat said:

Where does 4.3 and 23.8 degree come from? 

From transposing a photo on the forum into scalable vector graphics, where angles can be measured. Accuracy is debatable, but may be around 90% considering the subject photo quality (not the best).

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1 minute ago, MaxHugen said:

From transposing a photo on the forum into scalable vector graphics, where angles can be measured.

Like the seagulls then. 
 

look I get that clever stuff can be deduced from pics but unless you know that shot was completely 100% square on and you could precisely determine the centreline of the foil profile then it’s not going to be as precise as you would like it to be 

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16 hours ago, Forourselves said:

Im still picking an INEOS v Luna Rossa Prada Cup final

Nah mate, I'm going for American Magic vs. Luna Rossa.  Deano will be out for revenge.

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3 hours ago, MaxHugen said:

From transposing a photo on the forum into scalable vector graphics, where angles can be measured. Accuracy is debatable, but may be around 90% considering the subject photo quality (not the best).

Fun discussion on an excellent subject, am enjoying all of it.

About foil measurement devices, I once posted a long Foiling Week YT video that included  Bernasconi where he explained something about the lengths they went to during AC35 to verify just exactly what shapes and deformations were happening on the foils. He may also have given as a reason the necessity of trying match real-world observations against internal stress gauges and sim predictions. With flaps allowed in AC36, the same requirement may be even more important this time. 

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19 hours ago, FinnFish said:

INEOS will collapse inward when the pressure is applied. Can't build a team around one individual.

Ironic given your username that you ignore talent such as Giles Scott. 

I could point out the other talent and experience, but of course when that team had to deliver in a real race on foiling boats in the SailGP they really fell to bits. 

 

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Ineos look good in that video above. Not exactly ripping through the turns like Patriot is, but staying dry. Weird that "over the hill" view when they were a long way away. He is using a very long lens. Bit of a swell rolling in?

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INEOS will be fine with pressure. Historically that is not Ben's issue.  Luna Rossa on the other hand tends to explode with pressure, plus their crew selections often do not operate purely on merit.   

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5 minutes ago, Horn Rock said:

Ineos look good in that video above. Not exactly ripping through the turns like Patriot is, but staying dry. Weird that "over the hill" view when they were a long way away. He is using a very long lens. Bit of a swell rolling in?

The problem is that they are all bloody fast compared to almost everything else. They are doing dry turns a lot of the time (but all seem to have the occasional splash down).

Which is faster/fastest I don't think we have a hope of working out- how ever many seagulls fly past. Even assuming that there is a single answer and that in fact there isn't one boat faster in light winds, one in heavier winds etc

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6 minutes ago, enigmatically2 said:

The problem is that they are all bloody fast compared to almost everything else.

Still very early days with the B2's. I don't think Ineos is any where near fully optimised. Rig tension doesn't look to be really cranked on. No rake in the mast, and the fore stay looked to have a bit of sag.

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50 minutes ago, Horn Rock said:

Ineos look good in that video above. Not exactly ripping through the turns like Patriot is, but staying dry. Weird that "over the hill" view when they were a long way away. He is using a very long lens. Bit of a swell rolling in?

No swell, just a long way away. 

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1 hour ago, Horn Rock said:

Still very early days with the B2's. I don't think Ineos is any where near fully optimised. Rig tension doesn't look to be really cranked on. No rake in the mast, and the fore stay looked to have a bit of sag.

All the forestays have sag. It is called jib sheet tension.

I doubt any of the B2s are optimised yet.

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18 hours ago, hoom said:

For the record, flap rules (ver 1.10)

15 Foil flaps

15.1 A foil flap must be a linear component connected to a foil wing by a foil system.

15.2 Each foil shall include two foil flaps,

one lying entirely on one side of the foil wing symmetry plane, and
one lying entirely on the other side of the foil wing symmetry plane.

15.3 For the purposes of Rule 15:

(a) a “cross-section” is defined locally at any spanwise location along the rondure of the foil wing as a
section through a foil wing and foil flap, on a plane perpendicular to the rondure at that spanwise
location; and

(b) the “chord length” at a given cross-section and a given foil flap rotation angle is the distance between
the most forward point and the most aft point on the cross-section, when projected on to the foil
wing projection plane shown in Figure 13.1.

15.4 At any cross-section, the only permitted movement of a foil flap relative to a foil wing is a rotation about
an axis that remains approximately stationary with respect to the foil wing at that cross-section. This axis
must be designed to be stationary, but is permitted to have some movement resulting from:

(a) play in a mechanical bearing; or

(b) a flexure or soft hinge, such as a thin flexible material joining the foil flap to the foil wing.

15.5 Through a foil flap’s range of rotation angles and twists, a foil flap cross-section shall not significantly
deform except as permitted in Rules 15.4, 15.8 and 15.9, or as a result of external forces.

15.6 Both foil flaps of a foil shall have the same range of angular rotation and twist. With both foil flaps of a
foil centred in their ranges of motion, each foil flap shall be symmetric with respect to the other about
the foil wing symmetry plane, with a build tolerance of 3.0 mm.

15.7 At any cross-section and all rotation angles, when projected on to the foil wing projection plane, the length
of a foil flap must not be greater than 50% of the chord length. Hinges or other parts of a component which
occur at occasional cross-sections for connection purposes can be excluded from the projected lengths.

15.8 A foil flap may contact a foil wing, and in the absence of external forces, and at any cross-section and
rotation angle, either may cause deformation in the other in a single zone covering not more than 20% of
the local chord length. Outside this zone, neither shall cause deformation in the other.

15.9 Connections between sections of a foil flap are exempt from Rules 13.9, 15.4 and 15.5, providing such
connections span a combined total of no more than 10% of the span of a foil wing, where the span is
measured along the rondure

 

 

18 hours ago, hoom said:

At any cross-section there can be only one flap & operating on one axis.

But it envisages multiple sections connected flexibly & doesn't seem to require all sections to be on the same axis.

 

I thought we'd agreed back when B1 launches happened that at least a couple of the teams seemed to be using external hinges

a2820065-48-Flaps%2015.JPG

I'm not necessarily convinced its a fast solution but it seems to be what they're doing.

You can see its made of 2 parts in @mikenz2 pics.

Not seeing what you are seeing.

- 2 flaps per foil

- one on each side of the arm

Seems clear enough no?

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3 hours ago, Horn Rock said:

Ineos look good in that video above. Not exactly ripping through the turns like Patriot is, but staying dry. Weird that "over the hill" view when they were a long way away. He is using a very long lens. Bit of a swell rolling in?

At about 5 km, the horizon curve appears - unless you're a member of the Flat Earth Society, I guess, HR.

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11 minutes ago, Sailbydate said:

At about 5 km, the horizon curve appears - unless you're a member of the Flat Earth Society, I guess, HR.

I see you "rounders" have now even started altering videos on sailing forums to support your whacky round earth theories!

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1 hour ago, nav said:

 

 

Not seeing what you are seeing.

- 2 flaps per foil

- one on each side of the arm

Seems clear enough no?

15.9 that you quoted says that the flap can be in multiple sections, and that the join between them is exempt from some of the rules. So as long as the flap sections each rotate around an axis that is in the plane of the section of foil they attach to, no problem.

Apart from how to design that join and keep it smooth

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On 10/26/2020 at 8:28 AM, FinnFish said:

INEOS will collapse inward when the pressure is applied. Can't build a team around one individual.

So you either haven't bothered to look at their sailing roster or you are dismissing some of the best sailors in the world. I might be biased, but I think that overall, they have the strongest sailing roster. Just a few stand outs.....

Ben Ainslie - not bad 

Giles Scott - Only one Olympic gold (so far), 3rd AC Campaign

Iain "Goobs" Jensen - Gold and silver medals, considered by many to be the best "wing" trimmer in the world (I personally don't - I think he is equal best with Glenn Ashby) 3rd AC campaign

Xabi Fernandex - Gold and Silver Olympics 3rd AC campaign

Joey Newton - crew on 2 AC winners 5th AC Campaign

Then add the likes of Freddie Carr (3rd AC), Chris Brittle (4th AC) and Andrew Mclean (5th AC)

Let's not forget the CEO, Grant Simmer (only 4 AC wins across roles from sailor to design head to CEO), who has the best track record of anybody in AC management.

Does that really look like a team built around one individual? Or is the use of Ben Ainslie just a great marketing tool?

 

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They looked very fast in that video. Looked to me that the chase boat couldn't keep up? And the hull shape seems to be assisting with lift IMO. Let's hope Ben has learnt from the last AC in terms of a team approach? Can't wait until the December racing as we'll see some match racing and some sort of indicative feedback as to what the racing will look like?

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18 hours ago, MastaVonBlasta said:

Wow... The photos from @mikenz2  and then pimped up by @GeeJay show lots of interesting and confusing detail!
 

I've had a go at marking up, but... I just don't know. The photo of the top surface of the foil seems to show a number of 'hinge' lines, which one is real?

Could it be that the only actual hinge is '2'? It's the only one that has a continuous bright strip visible on the under-side. 

It's as if the leading edge section starts to bend down at '1'  (or hinge??) and its marked with a line of evenly space 'dimples'. From previous photos I assumed these were just low resolution effects on the actual hinge or flexible joint. But these enhanced and taken from closer distance photos seem to show that these are some flow conditioning/disturbing dimples...

Then at line '2', the inward part of the flap is hinged and is connected with a flexible patch marked '?'. Then line '2O' is not hinged and also has 'dimples' along it.

In any case, these foils don't seem agricultural to me...

Ineos-Foil_top-and-bottom.png

I suspect that the flap would start moving at you line 1.  You can see how the angles between the bulb and foil arms are all smooth until you get to line 1.  It then changes to a flat side on the bulb that would allow the flap to move free up and down.

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A couple of grainy close-ups to add to the foil discussion.

The first is just after the starboard foil has been raised, showing the flap still partly up (I think?) and the water flowing from what appears to be the lower trailing edge of the foil but is actually the gap between the fixed foil and flap - both sections of the flap are partly hidden due to the angle they are raised by.

The larger "tail" on the bulb in the first shot also looks like evidence that the flaps are up?

The next (a few seconds later) shows the flap back down but with a couple of streams of water still coming out of the gap.

foil-1.jpg

foil-2.jpg

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7 minutes ago, The_Alchemist said:

Speed calc of about 36 knots near the end of the video.

Any chance you could get a calc of any of the boats' speed at take-off?  19 knots (on one foil) has been quoted, but seems a bit high to me...

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5 minutes ago, MaxHugen said:

Any chance you could get a calc of any of the boats' speed at take-off?  19 knots (on one foil) has been quoted, but seems a bit high to me...

It would be difficult.  There is not a lot of video of the take offs and most of them are not perpendicular to the camera with a stationary point of reference.

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1 minute ago, Indio said:

That Jonathan Livingston gets around...:)

It appears he's...

Lost
On a painted sky
Where the clouds are hung
For the poet's eye

Got that album on vinyl and CD. Can't say kids are a fan (yet). Philistines...

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13 minutes ago, The_Alchemist said:

It would be difficult.  There is not a lot of video of the take offs and most of them are not perpendicular to the camera with Understand. a stationary point of reference.

Understood.   There was a video not long after Te Aihe's launch (I think) that showed her taking off in calm water in the harbour, reasonably close to perpendicular... but of course I can't find that vid now!

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50 minutes ago, The_Alchemist said:

It would be difficult.  There is not a lot of video of the take offs and most of them are not perpendicular to the camera with a stationary point of reference.

I know I am delinquent on this, but is there a post that explains the methodology you are using to calculate the boat speed?

 

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2 hours ago, nroose said:

I know I am delinquent on this, but is there a post that explains the methodology you are using to calculate the boat speed?

 

Guess work.. 

they are only square on to the camera  with 33 seconds left of the video and then rapidly start moving away messing up any accuracy 

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4 hours ago, weta27 said:

A couple of grainy close-ups to add to the foil discussion.

The first is just after the starboard foil has been raised, showing the flap still partly up (I think?) and the water flowing from what appears to be the lower trailing edge of the foil but is actually the gap between the fixed foil and flap - both sections of the flap are partly hidden due to the angle they are raised by.

The larger "tail" on the bulb in the first shot also looks like evidence that the flaps are up?

The next (a few seconds later) shows the flap back down but with a couple of streams of water still coming out of the gap.

foil-1.jpg

foil-2.jpg

Well spotted @weta27

To me it looks as if the flap is indeed not along the full width of the foil wing and it's more likely at that '2' line I've marked before.

The spray and brighter line seem to be starting aft of the 'half-chord' line '1'.

Interestingly, in the second photo, the lowest bit of spray seems to be where the flexible (rubber?) patch would end, just beyond the kink.

The actual movable flap would be the part marked in yellow?

 

Ineos-GapSplash.png

IneosFlapSection2.PNG

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3 minutes ago, MastaVonBlasta said:

Well spotted @weta27

To me it looks as if the flap is indeed not along the full width of the foil wing and it's more likely at that '2' line I've marked before.

The spray and brighter line seem to be starting aft of the 'half-chord' line '1'.

Interestingly, in the second photo, the lowest bit of spray seems to be where the flexible (rubber?) patch would end, just beyond the kink.

The actual movable flap would be the part marked in yellow?

 

Ineos-GapSplash.png

IneosFlapSection2.PNG

Could lines 1 & 2 both be hinges in a Fowler Flap arrangement?

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19 minutes ago, MastaVonBlasta said:

They look quite fast in this clip!

And is the guy at the very back sending emails while on the boat...? ;)

 

LaptopSailor.PNG

No way we can just see the difference between 35 and 40, and those are very different speeds. I calculate 34 at about the time of that still.

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38 minutes ago, Indio said:

Could lines 1 & 2 both be hinges in a Fowler Flap arrangement?

Fowler Flap: "A split flap that slides backwards, before hinging downward, thereby increasing first chord, then camber."  I think that falls outside of the Rules:

15.4 At any cross-section, the only permitted movement of a foil flap relative to a foil wing is a rotation about an axis that remains approximately stationary with respect to the foil wing at that cross-section. This axis must be designed to be stationary...

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3 hours ago, JALhazmat said:

Guess work.. 

they are only square on to the camera  with 33 seconds left of the video and then rapidly start moving away messing up any accuracy 

I didn't actually ask you, but as you seem to know, perhaps you can explain the methodology, including why it matters that they be square to the camera?

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5 minutes ago, nroose said:

I didn't actually ask you, but as you seem to know, perhaps you can explain the methodology, including why it matters that they be square to the camera?

No I am just sceptical as to the accuracy.

alchy will explain it 

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10 minutes ago, nroose said:

I didn't actually ask you, but as you seem to know, perhaps you can explain the methodology, including why it matters that they be square to the camera?

Boat is 75ft, so you are measuring how long the boat takes to cover it's own length i.e. against a reference object (wave crest, crane) in background. If boat is at an angle, it will take longer to cover the distance. Easiest to think about it at extreme angles to viewer...

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1 hour ago, RobG said:

Only need 1 boat length.

You mean capturing the time interval between the bow passing an object and the stern?

These boats are 75ft long. Let us assume that they are doing 40kts. That means that they will move one boat length in about 1.1s

But if they were doing 35kts it would take 1.27s a difference of 0.16s

Even if the boat were square on its very unlikely that you could measure the time difference more accurately than that because of human reaction times, video rate etc (noting that with standard video at 24fps, one frame at the start and one at the end would equate to half of that time interval).

The angle of the boat to the camera would always lead to an underestimation of the speed, 10 degrees equates to a 1.5% underestimate ; 20 degrees equates to a 6% underestimate; 30 degrees equates to 14% underestimate. Those are relatively low in comparison, but I would point out that there is something about these boats that tends to make you think you are more square on than you are based on my observations

And that is before you get into the difficulties of comparing boat with boat which requires an understanding of wind conditions AWA/TWA, sea state and knowledge of what the crew were trying to test out at the time.

 

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32 minutes ago, Chris UK said:

Boat is 75ft, so you are measuring how long the boat takes to cover it's own length i.e. against a reference object (wave crest, crane) in background. If boat is at an angle, it will take longer to cover the distance. Easiest to think about it at extreme angles to viewer...

It matters not whether the boat is at an angle to the camera. You do have to measure the bow to the center of the stern. It does matter if the hull is at an angle to it's direction of travel or if it is turning at the time. So the accuracy is relative to how well you identify the center of the stern and the amount of angle of the hull relative to the direction of travel., as well as the accuracy of the frame timing on the video. Seems reasonable to assume we could estimate within 2 or 3 frames, which would be about 10%.

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33 minutes ago, nroose said:

as well as the accuracy of the frame timing on the video

As well as wether the frames you are looking at are interpolated or not, and what other affects have been applied to the video. The time between frames is not a known factor without knowing the settings used to encode the video, the algorithm used, and some form of reference timecode.

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2 hours ago, nroose said:

Oh, and the hull is 68.5 feet, no? With a 6.5 foot sprit?

Rule 11.3 The forward most point on the hull shall be no less than 20.600 m and no greater than 20.700 m from TRP(67.59 ft - 67.91 ft)
17.2 The bowsprit shall extend from the hull to at least 22.760 m forward of TRP. (74.67 ft)
17.3
No part of the bowsprit shall be:(a) forward of a plane 22.860 m forward of TRP (75.00 ft)

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8 hours ago, nroose said:

I know I am delinquent on this, but is there a post that explains the methodology you are using to calculate the boat speed?

 

Well, JALHazmat thinks it is magic, so let's just keep it between us.  I heard he got real upset when he found out how the Easter Bunny and the Tooth Fairy worked.  :D

 

I dug up some of the earlier discussion on how I did the calculations.  I get the time it take for one boat length (hull w/o bowsprit) to pass a stationary object.  Time from the frame rate of the video (typically 25 or 30 frames/sec), step through and count the frames.  I typically try to get multiple readings

It doesn't really work if the camera is moving, like traveling in another boat (unless you know the boat speed).  I usually noted that the speed is typically within about 2 knots of accuracy, but posted the speed in tenths of a knot to show differences in speed. (e.g. 23.5 knots going in one direction is slower than the 24.4 knots going in the other direction).  One time I even used the speed of a seagull to prove that the UK video had been speed up to 2x speed.

 

Here are some good speed estimates for when you look at a video.  The camera must be stationary (not in a moving boat) and exclude the bowsprit from the length of the hull.

If you count out the time it takes for the hull to pass a stationary object.  Count by using the old:  1 one thousand 2 one thousand (each being a ~0:25 secs), or use a timer...

time              speed

0.75 sec     53 knots

1.00 sec     40 knots

1.25 sec     32 knots

1.50 sec     27 knots

1:75 sec     23 knots

2.00 sec     20 knots

2.25 sec     16 knots

 

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I'll be honest Alchemist, I don't think you can get to 2kts of accuracy for the reasons I gave in my post (which you kindly liked). I think at best you can claim +/ 5kts at the sort of speeds these boats are going. And that is assuming a timer not relying on verbal counting

p.s. I completely agree with JonRowe's point that frame rate is not enough on its own, the coding can make a difference. Hence why I allowed a complete frame at start and end. I reckon that is the best you can do.

 

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12 minutes ago, The_Alchemist said:

I dug up some of the earlier discussion on how I did the calculations.  I get the time it take for one boat length (hull w/o bowsprit) to pass a stationary object.  Time from the frame rate of the video (typically 25 or 30 frames/sec), step through and count the frames.  I typically try to get multiple readings

How do you go through a video frame by frame?

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