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53 minutes ago, uflux said:

No country for old men :rolleyes:

People must have rose tinted glasses when viewing history. In the IACC boats there were some great matches, but there was some real boring racing as well. One you were  200 meters behind you had very little chance. 

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6 minutes ago, mako23 said:

People must have rose tinted glasses when viewing history. In the IACC boats there were some great matches, but there was some real boring racing as well. One you were  200 meters behind you had very little chance. 

Sure, but a 200m lead would IIRC represent more than a minutes lead and you could still see the two boats in the same shot no problem.

A 1 minute lead in these boats puts them in different postal codes.

Also, a small fuck up that takes you off your foils ends the race - even more so than the AC50s.

With the IACCs, you could blow a spinnaker, lose 3 or 4 boat lengths and get straight back into it.

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1 hour ago, Priscilla said:

Foiling definitely gives you a WOW factor and it looks great to TV to see two boats screaming towards each other at 40 knots, but it also can kill the racing. If one team make a small mistake, that can be the ballgame right there. If the leader doesn't make a mistake and there are stable wind conditions up and down the course, the trailing team is most likely done for the race.

4ksb racing can be tedious to watch, but it makes it more about the designers, sailors and match racing tactics. Right now, it comes down to the foil designers and who makes the first mistake.

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22 hours ago, Sailbydate said:

Keel bolts?

yup, some even going so far as to use washers too !!!   who'da thought.........

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2 hours ago, Brutal said:

If one team make a small mistake, that can be the ballgame right there.

That's not what we've seen from ETNZ. They've made heaps of mistakes, and come right back into it.

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Patriot support boat just set a top mark bouy in between Taka and Tiri. 

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5 hours ago, The_Alchemist said:

1962232605_AMPatkeeladj.jpg.e9f77e05365dd9afea9d4629ba11cdfc.jpg

You can clearly see that they have added a strip down the front of the keelson. to give it closer contact to the water.  It look like the flatten out the shape and extend the depth at the back of the original keelson

I still struggle to visualise the airflow around that hull providing an "end plate" effect.   I'm more inclined to think these strips could have more to do with trying to reduce the induced drag from the hull.  Guessing as always, but I think Di must be quite substantial. :)

 

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If you blew a corner in F1 racing, or make any other mistake, the competition is gone.  Same thing here with the AC75. The problem isn't the speed differential, it's that the teams are still learning how to control these boats. That is the aspect that we aren't used to seeing at the pinnacle of any sport.

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2 minutes ago, tDot said:

If you blew a corner in F1 racing, or make any other mistake, the competition is gone.  Same thing here with the AC75. The problem isn't the speed differential, it's that the teams are still learning how to control these boats. That is the aspect that we aren't used to seeing at the pinnacle of any sport.

Well it depends on what you mean by "blew a corner". If by blew you mean crash, sure you are correct.

But this is not an appropriate analogy IMO, since the equivalency in these boats would be capsized since BOTH events prevent further racing.;

But with the AC75s, it is possible to crash off the foils and then get back up on them and continue racing. However, by the time you have done that the other boat is 1km + ahead and the only thing that can bring the race back from the precipice is your competitor doing the same.

The better analogy is a missed gear change, fucked approach to the corner or shit pit stop.

 I am sure F1 is littered with victors who fucked gear changes, approaches to corners and pit stops.

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1 minute ago, jaysper said:

Well it depends on what you mean by "blew a corner". If by blew you mean crash, sure you are correct.

But this is not an appropriate analogy IMO, since the equivalency in these boats would be capsized since BOTH events prevent further racing.;

But with the AC75s, it is possible to crash off the foils and then get back up on them and continue racing. However, by the time you have done that the other boat is 1km + ahead and the only thing that can bring the race back from the precipice is your competitor doing the same.

The better analogy is a missed gear change, fucked approach to the corner or shit pit stop.

 I am sure F1 is littered with victors who fucked gear changes, approaches to corners and pit stops.

I don't think anyone in F1 misses gear changes anymore.  Not with electronic double clutch transmissions. But maybe they still do.

I'm not talking about crashing, if they miss an Apex and lose a couple seconds or set up poorly for a major straight. Then that's all it takes for them to be seconds behind.

Pit stops are definitely culprits too. 

But again, these are small mistakes that can add up to huge differentials. That distance is very difficult to make up, though not impossible, and often the competition making a mistake is the easiest way to recover.  Similar to what we are seeing with the AC75.

In the world of foiling, coming off the foils is a major mistake. So not surprisingly it has major consequences. 

 

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1 minute ago, tDot said:

I don't think anyone in F1 misses gear changes anymore.  Not with electronic double clutch transmissions. But maybe they still do.

I'm not talking about crashing, if they miss an Apex and lose a couple seconds or set up poorly for a major straight. Then that's all it takes for them to be seconds behind.

Pit stops are definitely culprits too. 

But again, these are small mistakes that can add up to huge differentials. That distance is very difficult to make up, though not impossible, and often the competition making a mistake is the easiest way to recover.  Similar to what we are seeing with the AC75.

In the world of foiling, coming off the foils is a major mistake. So not surprisingly it has major consequences. 

 

So by missing gear I don't mean physically missing the gates since the (presumably solenoids) perform this function but rather failing to change at the right time.

However as you said, missing an apex is seconds behind. Crashing off the foils is up to a minute behind or more.

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it would be the equivalent of losing turbo charging for a period... or being stuck in 2nd gear (i've got an error on the gearbox computer is a real thing)

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Text from son at Takapuna "Dad Amway is just off the beach" I reply cool send me a decent picture.

Screen_Shot_2021-01-05_at_5_21.44_PM.thumb.png.2590642703d62287cdab065723c86185.png

 

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6 minutes ago, Priscilla said:

Text from son at Takapuna "Dad Amway is just off the beach" I reply cool send me a decent picture.

Screen_Shot_2021-01-05_at_5_21.44_PM.thumb.png.2590642703d62287cdab065723c86185.png

 

Glad to see he’s got his priorities right. You brought him up well. 

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4 hours ago, Horn Rock said:

That's not what we've seen from ETNZ. They've made heaps of mistakes, and come right back into it.

I think the ETNZ position is that they were strategic  “sandbagging” mistakes :P

 

 

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44 minutes ago, Ex-yachtie said:

Glad to see he’s got his priorities right. You brought him up well. 

Magnificent! I love her...um...bustle.

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What boat?

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1 hour ago, Priscilla said:

Text from son at Takapuna "Dad Amway is just off the beach" I reply cool send me a decent pic.

Screen_Shot_2021-01-05_at_5_21.44_PM.thumb.png.2590642703d62287cdab065723c86185.png

 

They'd bestt watch out, or InEOS will be copying her hull profile...

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4 hours ago, MaxHugen said:

I still struggle to visualise the airflow around that hull providing an "end plate" effect.   I'm more inclined to think these strips could have more to do with trying to reduce the induced drag from the hull.  Guessing as always, but I think Di must be quite substantial. :)

 

It's simple, the windward side of the sails+hull has higher pressure than the lee side. The air can't pass from high to low pressure anywhere between the sails and the hull, because all the gaps are sealed. It can only cross at the top of the sail and under the hull. You can't do anything about the top, but you can seal the gap under the hull with the keel.  It makes a huge difference. Effective aspect ratio is doubled (look at your induced drag equation what that does with induced drag).

If you've ever windsurfed, you know that as soon as you close the sail down to the board, you switch into another gear by eliminating all those vortices and induced drag.

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8 minutes ago, erdb said:

It's simple, the windward side of the sails+hull has higher pressure than the lee side. The air can't pass from high to low pressure anywhere between the sails and the hull, because all the gaps are sealed. It can only cross at the top of the sail and under the hull. You can't do anything about the top, but you can seal the gap under the hull with the keel.  It makes a huge difference. Effective aspect ratio is doubled (look at your induced drag equation what that does with induced drag).

If you've ever windsurfed, you know that as soon as you close the sail down to the board, you switch into another gear by eliminating all those vortices and induced drag.

I am having some issues with the amt of Induced Drag - very high!   I'm using the equation provided by @Basiliscus:

Lift^2 / ( PI * e (Di_Efficiency) * (0.5 * Density_Air|Water * Velocity (ms)^2 * Span^2 )

I assume that you are doubling the 'Span' to account for 'end plating'?

That's problematic in my mind, as the pic of AM above shows a substantial gap between hull skeg and sea surface - doesn't seem like very effective end plating to me?

Also did some calcs for TR in Race 4 of the ACWS.  At ~15 knots they consistently foiled with a Median Arm Cant of 63° upwind.  At this angle, with the foil tip just out of the water, I calculate the avg height of the bustle from water surface to be about 0.5m.   Again, I don't think this really qualifies as effective end plating...

I don't have facts.

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About the return to non-foiling mono's - I heard recently that the origins of the AM challenge were similar to that of Prada in that Fauth and De Vos were both expecting a more traditional monohull package in this AC, that was what they fronted their money for (makes sense based on their histories in the TP and Maxi72 fleets). Apparently at least Hap Fauth has been so far quite unimpressed with the amount of cash he's been throwing at something that doesn't tickle his fancy - this may have changed since the Xmas regatta after AM put in a solid performance. 

Part of me would be quite keen on the 100ft mono proposal - as much as the 75s are spectacular it would also be quite cool to have the quality of video and comms coverage available today onboard a boat with actual sail manouvres and more 'dynamic' crew work (The go-pro vids of the Quantum TP team are about as close as we can get right now). 

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38 minutes ago, OldWoodenShip said:

The span is squared (not doubled) because it forms part of the aspect ratio.

Have a look here for a brief overview: https://www.grc.nasa.gov/www/k-12/airplane/induced.html.

Thanks, yes I understand that.

I should have been more explicit... I was referring to doubling the sail span (height) first - to account for the "end plating" - before squaring it.

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1 hour ago, MaxHugen said:

Thanks, yes I understand that.

I should have been more explicit... I was referring to doubling the sail span (height) first - to account for the "end plating" - before squaring it.

Not quite. You (roughly) double the aspect ratio if the foil is end plated, not the span.  That means you double the span after squaring it - otherwise you’ll quadruple the AR. 

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Vittorio & Pietro’s latest video, on Patriot’s “Louboutin 12 cm pumps stance”, not a bad similitude

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Patriot's silhouette has always reminded me of a particular style of chef's knife...

g-7_1.jpg

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17 hours ago, Brutal said:

Foiling definitely gives you a WOW factor and it looks great to TV to see two boats screaming towards each other at 40 knots, but it also can kill the racing. If one team make a small mistake, that can be the ballgame right there. If the leader doesn't make a mistake and there are stable wind conditions up and down the course, the trailing team is most likely done for the race.

4ksb racing can be tedious to watch, but it makes it more about the designers, sailors and match racing tactics. Right now, it comes down to the foil designers and who makes the first mistake.

Nascar did a unique take on this.  Let's make the races 1 leg, after which the lead boat has to wait for the boat behind to catch before starting the next leg.

Nascar does their racing in stages to recompress the field.

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3 hours ago, fish7yu said:

 

At about 10:30 they do an interesting maneuver.  They also scare the hell out of the jet skier...

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29 minutes ago, The_Alchemist said:

At about 10:30 they do an interesting maneuver.  They also scare the hell out of the jet skier...

Double gybe to make a mark you're under-stood on then upwind?Good thing to practice.  

 

Seems like AM has really developed their systems and crew work. I have to wonder if they're hitting the limits on their boat though.  Originally I thought the traditional boom, for example, would be nice from a simplicity and reliability point of view, but the battens/chokers/rams of NZ gives them so many more options and room for improvememnt. It seems like they were at least similar pace with as light edge to NZ at the XMas Xup,  but how close are they both to fully realized?  Gut feeling is they're close now but NZ has a much higher ceiling. 

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Several things:

1) The short luff jibs seem to have gone to the bottom of the sail locker after the Christmas Regatta.  I conclude that ETNZ almost exclusive use of big jib is the reason for this. During the racing ETNZ accelerated out of tacks faster and this might well have been because of the bigger jib.  The small jib may be faster in a straight line, but does not race as well.

2) We should expect more racing errors and boat handling problems because the work up regattas were cancelled.  These are very talented crews, but there is no substitute for actual boat on boat competition.  This boat on boat training was banned by the protocol, and canceled by Covid and this is a novel class racing in its first regattas.  See the above as one of the first adjustments.

3) After the DOG fight, Oracle under the guise of ACM conducted a series of screen tests to determine what type of vessel would produce the most compelling television.  IF you were going to restructure a traditional event to turn it into a televised spectacle, this was totally sensible.  I believe they used RC44s and GP 32s as test beds.  You know what they concluded.  If you can accept that this was a good faith effort, it would seem that going back to TP52 style monohull, which while very good race boats, would be bad for the commercialization of the Cup. 

4)  There are other legitimate goals for the America’s Cup.  One might seek to have more participation in an International Sporting Event far more like the 12 meter and IACC days.  Certainly those boats were more accessible to a greater pool of owners and syndicates and provided more employment for the rank and file Yachting Professionals.   You could easily argue that 10 teams racing anything would be better sport than the  4 extraordinary specialized boats we see in New Zealand.  As an economic proposition to a host community, participation is better than broadcasting.

SHC

 

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10 hours ago, MaxHugen said:

I am having some issues with the amt of Induced Drag - very high!   I'm using the equation provided by @Basiliscus:

Lift^2 / ( PI * e (Di_Efficiency) * (0.5 * Density_Air|Water * Velocity (ms)^2 * Span^2 )

I assume that you are doubling the 'Span' to account for 'end plating'?

That's problematic in my mind, as the pic of AM above shows a substantial gap between hull skeg and sea surface - doesn't seem like very effective end plating to me?

Also did some calcs for TR in Race 4 of the ACWS.  At ~15 knots they consistently foiled with a Median Arm Cant of 63° upwind.  At this angle, with the foil tip just out of the water, I calculate the avg height of the bustle from water surface to be about 0.5m.   Again, I don't think this really qualifies as effective end plating...

I don't have facts.

It's not an ON /OFF effect. Even if it's not a perfect seal, the smaller the gap the better. I vaguely remember a story in the Marchaj book when they looked at Dragon models with a flush deck or with the cabin, and they were surprised that the little cabin actually improved upwind performance by filling the gap between the boom and the hull. They also found that it's most important to close the gap close to the leading edge of the sails, whereas farther aft is less important.

Also, real life is different from these simple static models and calculations we can do. There are gusts and shifts, the boat's heel and pitch angles keep changing, there are waves, the ride height is not constant either, so that 0.5m gap can be close to zero for 30% of the time. I'm sure the teams are also training hard to get better at controlling their height to minimize that gap.

 

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46 minutes ago, erdb said:

It's not an ON /OFF effect. Even if it's not a perfect seal, the smaller the gap the better. I vaguely remember a story in the Marchaj book when they looked at Dragon models with a flush deck or with the cabin, and they were surprised that the little cabin actually improved upwind performance by filling the gap between the boom and the hull. They also found that it's most important to close the gap close to the leading edge of the sails, whereas farther aft is less important.

Also, real life is different from these simple static models and calculations we can do. There are gusts and shifts, the boat's heel and pitch angles keep changing, there are waves, the ride height is not constant either, so that 0.5m gap can be close to zero for 30% of the time. I'm sure the teams are also training hard to get better at controlling their height to minimize that gap.

So for the induced drag equation, are you using Span2, or (Span*2)2, or (Span2)*2... or something else?

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5 minutes ago, MaxHugen said:

So for the induced drag equation, are you using Span2, or (Span*2)2, or (Span2)*2... or something else?

Aspect ratio is defined as span / mean chord. The confusion comes from how you get this ratio. For simplicity, instead of calculating a mean chord, you can use span^2 / area. It's the same thing, because area = span x mean chord, so basically you're dividing span^2 with (span x mean chord) and arrive to the same span / mean chord ratio.

For the sails, I get the induced drag from the vortex sheet, for the foils, I use span^2 / area.

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4 hours ago, NZK said:

Patriot's silhouette has always reminded me of a particular style of chef's knife...

g-7_1.jpg

 

With the rudder as heel, the Louboutin look is more fitting

 

 

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4 minutes ago, Xlot said:

 

With the rudder as heel, the Louboutin look is more fitting

 

 

 

4 hours ago, NZK said:

Patriot's silhouette has always reminded me of a particular style of chef's knife...

g-7_1.jpg

That is an interesting observation NZK. Then would this represent INEOS?

The Best Meat Cleaver: A Complete Guide To Choose The Right One - Knife  Planet

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3 hours ago, RMac said:

Double gybe to make a mark you're under-stood on then upwind?Good thing to practice.  

 

Seems like AM has really developed their systems and crew work. I have to wonder if they're hitting the limits on their boat though.  Originally I thought the traditional boom, for example, would be nice from a simplicity and reliability point of view, but the battens/chokers/rams of NZ gives them so many more options and room for improvememnt. It seems like they were at least similar pace with as light edge to NZ at the XMas Xup,  but how close are they both to fully realized?  Gut feeling is they're close now but NZ has a much higher ceiling. 

In the interview with Goodison he talked about how they feel there is so much better control of the main when you use a boom.  He says that he is constantly asking for more buttons on his sail trim controller so he can try new adjustments. Another interesting point he made is how you can really change the tuning of the sails with just the mast rotation.  It sounds like you could really sandbag it by just making some subtle changes in the mast rotation that may be hard to detect.

https://yachtracing.life/the-yacht-racing-podcast-americas-cup-special-part-2-paul-goodison/ )

I think that AM still has a tremendous amount of room for improvements in their maneuvers.  Even the broadcasters mention how they were not as polished on their turns and you could see them lose ground on every turn.  I think they were way too conservative and losing speed and VMG.   You can see them out making quicker turns and dropping the second foil much later.

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16 minutes ago, The_Alchemist said:

In the interview with Goodison he talked about how they feel there is so much better control of the main when you use a boom.  He says that he is constantly asking for more buttons on his sail trim controller so he can try new adjustments. Another interesting point he made is how you can really change the tuning of the sails with just the mast rotation.  It sounds like you could really sandbag it by just making some subtle changes in the mast rotation that may be hard to detect.

https://yachtracing.life/the-yacht-racing-podcast-americas-cup-special-part-2-paul-goodison/ )

I think that AM still has a tremendous amount of room for improvements in their maneuvers.  Even the broadcasters mention how they were not as polished on their turns and you could see them lose ground on every turn.  I think they were way too conservative and losing speed and VMG.   You can see them out making quicker turns and dropping the second foil much later.

If "better control" means the adjustment points holding their position better, for sure.  I originally thought the booms would be superior as you have a stiffer control member so wouldn't have the sail changing with wind stretngth. BUT.  The incredible depth of the mains means that the boom is a limiting factor. I mean you can ease both outhaul rams to get the clews fwd, but eventually the shape of the boom is distorting the bottom of the sail, and you also have no (or at least less) batten control of the shape of the foot. The boats with the weirdo battens/guys/rams, panels are able to make the mains incredibly deep, and then send them right back to flat (ish) as the boat accelerates.  I think out of turns and in light air the soft booms are better. 

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24 minutes ago, The_Alchemist said:

In the interview with Goodison he talked about how they feel there is so much better control of the main when you use a boom.  He says that he is constantly asking for more buttons on his sail trim controller so he can try new adjustments. Another interesting point he made is how you can really change the tuning of the sails with just the mast rotation.  It sounds like you could really sandbag it by just making some subtle changes in the mast rotation that may be hard to detect.

https://yachtracing.life/the-yacht-racing-podcast-americas-cup-special-part-2-paul-goodison/ )

I think that AM still has a tremendous amount of room for improvements in their maneuvers.  Even the broadcasters mention how they were not as polished on their turns and you could see them lose ground on every turn.  I think they were way too conservative and losing speed and VMG.   You can see them out making quicker turns and dropping the second foil much later.

Sounds like they need a good Penguin sailor to trim main!

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2 minutes ago, RMac said:

If "better control" means the adjustment points holding their position better, for sure.  I originally thought the booms would be superior as you have a stiffer control member so wouldn't have the sail changing with wind stretngth. BUT.  The incredible depth of the mains means that the boom is a limiting factor. I mean you can ease both outhaul rams to get the clews fwd, but eventually the shape of the boom is distorting the bottom of the sail, and you also have no (or at least less) batten control of the shape of the foot. The boats with the weirdo battens/guys/rams, panels are able to make the mains incredibly deep, and then send them right back to flat (ish) as the boat accelerates.  I think out of turns and in light air the soft booms are better. 

However. This only really impacts at any level just above or below the boom. Their boom is a deck sweeper, contoured to follow the deck shape, so the distorted portion is nominal. They are still sealing off the flow at deck level.

They must figure that this distortion is of little consequence compared to the improved sail control of a stiff boom. Otherwise you’d see them adopt it like all others have.

 

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5 hours ago, NZK said:

Patriot's silhouette has always reminded me of a particular style of chef's knife...

LR-PP LR-PP.thumb.JPG.d84d17c7d59dc224c5763c4c23a184e4.JPG

Team Brexit Ineos229805245_IneosChopper.thumb.JPG.d82f3f3ae2c8046efeb8bb78a296230d.JPG

AM

UCUC3345-AM.thumb.jpg.ef1b8bb1bc05a46b486384b7173c4cfe.jpg

ETNZETNZ-honshu.thumb.jpg.e98af442b1ebae8037685df9acf7c5f2.jpg

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1 hour ago, Ex-yachtie said:

ETNZ

(Sorry, but it had to be done). 

2A012948-DAD6-4861-96F1-B32CF93D05D2.jpeg

Don't bring a knife to a gunfight. But don't bring a popgun to a real gunfight, either.

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2 hours ago, Ex-yachtie said:

ETNZ

(Sorry, but it had to be done). 

2A012948-DAD6-4861-96F1-B32CF93D05D2.jpeg

The gun is stretching the metaphor a bit much...

 

However, ETNZ is next-gen knife...

images (19).jpeg

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2 hours ago, Ex-yachtie said:

ETNZ

(Sorry, but it had to be done). 

 

2 hours ago, Ex-yachtie said:

ETNZ

(Sorry, but it had to be done). 

2A012948-DAD6-4861-96F1-B32CF93D05D2.jpeg

 

If you know anything about 1911 pistols, this particular model is high on flash and low on function.  Are  you comparing it to ETNZ?

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3 minutes ago, pluscount said:
If you know anything about 1911 pistols, this particular model is high on flash and low on function.  Are  you comparing it to ETNZ?

.45 ACP is the only way to go. Makes an unforgettable  impression on whatever is on the receiving end.

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4 hours ago, Rasputin22 said:

 

That is an interesting observation NZK. Then would this represent INEOS?

The Best Meat Cleaver: A Complete Guide To Choose The Right One - Knife  Planet

Nah here is my teams boat

Screenshot (1701) - Copy - Copy.png

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Nah, the teapot is functional... 8)

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13 minutes ago, accnick said:

.45 ACP is the only way to go. Makes an unforgettable  impression on whatever is on the receiving end.

You did notice that this pistol is .22 long rifle I hope.

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24 minutes ago, pluscount said:
If you know anything about 1911 pistols, this particular model is high on flash and low on function.  Are  you comparing it to ETNZ?

It was a "gun to a knife fight" quip. I don't give a fuck about guns or anyone who thinks they're cool or a "right".

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1 hour ago, pluscount said:

You did notice that this pistol is .22 long rifle I hope.

Ya think? That's why I said don't bring a popgun to a real gunfight.

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1 hour ago, Ex-yachtie said:

It was a "gun to a knife fight" quip. I don't give a fuck about guns or anyone who thinks they're cool or a "right".

Hot and bothered?

Tell us how you really feel Ex...:)

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59 minutes ago, Kiwicupfan said:

Sent that to my non sailing friends who have known me for years , know the sport and I have taken out on TP52s , J109s, MORC30s and Vipers and generally unimpressed with sailing... their collective  reaction to this video is “dude that if fucking sick” . 

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11 hours ago, NZK said:

Patriot's silhouette has always reminded me of a particular style of chef's knife...

g-7_1.jpg

That's pretty sharp, NZK. ;-)

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8 hours ago, erdb said:

Aspect ratio is defined as span / mean chord. The confusion comes from how you get this ratio. For simplicity, instead of calculating a mean chord, you can use span^2 / area. It's the same thing, because area = span x mean chord, so basically you're dividing span^2 with (span x mean chord) and arrive to the same span / mean chord ratio.

For the sails, I get the induced drag from the vortex sheet, for the foils, I use span^2 / area.

OK, I thought you were also calculating the sail induced drag from @Basiliscus 's previous posts.

Still looking for a good tech article that considers end plate... and how to deal with 'partial' end plate effect.

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5 hours ago, barfy said:

Hot and bothered?

Tell us how you really feel Ex...:)

Watched AM and LR train while having a swim off the bays this afternoon. I feel better now. 

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1 hour ago, Ex-yachtie said:

Watched AM and LR train while having a swim off the bays this afternoon. I feel better now. 

Awesome!!! I chased errant cows through deep bush in 28 degrees for three hours. Swim tomorrow..or kill fish

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On 1/6/2021 at 12:07 AM, sosoomii said:

Not quite. You (roughly) double the aspect ratio if the foil is end plated, not the span.  That means you double the span after squaring it - otherwise you’ll quadruple the AR. 

In this Span Squared | North Sails article they illustrate that the 'reflected' span is included in "span" measurement prior to the drag calc. Span in my calcs is sail height, so now I've doubled it before it gets squared. Seems right, the drag distribution is looking far more realistic:

image.png.d33dfc44a4b5815dcf47508ecb18ad06.png

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43 minutes ago, MaxHugen said:

In this Span Squared | North Sails article they illustrate that the 'reflected' span is included in "span" measurement prior to the drag calc. Span in my calcs is sail height, so now I've doubled it before it gets squared. Seems right, the drag distribution is looking far more realistic:

image.png.d33dfc44a4b5815dcf47508ecb18ad06.png

That North article is good, and it is ultimately span that matters not AR. But end plating one end of a foil will not quadruple the effective aspect ratio.  In reality it won’t even double it. See NACA Tech Note 2440, Table 1 for example. http://naca.central.cranfield.ac.uk/reports/1951/naca-tn-2440.pdf
 

6F14B46C-3736-4234-A576-AF461702FE70.jpeg

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1 hour ago, sosoomii said:

That North article is good, and it is ultimately span that matters not AR. But end plating one end of a foil will not quadruple the effective aspect ratio.  In reality it won’t even double it. See NACA Tech Note 2440, Table 1 for example. http://naca.central.cranfield.ac.uk/reports/1951/naca-tn-2440.pdf

Hmmm... that's from 1951.

North Sails appears to use Span*2 (shown as 'b' below) but there is no specific reference to end-plating of a sail.

image.png.d811469c63084270681bea69aad8651d.png

Not easy finding anything specific on this topic!

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3 hours ago, MaxHugen said:

In this Span Squared | North Sails article they illustrate that the 'reflected' span is included in "span" measurement prior to the drag calc. Span in my calcs is sail height, so now I've doubled it before it gets squared. Seems right, the drag distribution is looking far more realistic:

image.png.d33dfc44a4b5815dcf47508ecb18ad06.png

 Nice, but the rudder contribution seems a lot, no?

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2 hours ago, Xlot said:

 Nice, but the rudder contribution seems a lot, no?

Quite agree, have to recheck the calcs for that.  I have equations coming out of my ears!  :wacko:

The "Spray" is also a bit suss I think.

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3 hours ago, MaxHugen said:

Hmmm... that's from 1951.

LOL. So? The physics hasn’t changed! 

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3 hours ago, MaxHugen said:

Hmmm... that's from 1951.

North Sails appears to use Span*2 (shown as 'b' below) but there is no specific reference to end-plating of a sail.

image.png.d811469c63084270681bea69aad8651d.png

Not easy finding anything specific on this topic!

Max, it doesn't matter how you calculate AR - whether you use span / mean chord or span^2 / area. It's the same thing once you replace area with span x mean chord.

When you double AR assuming a perfect seal under the sails, you can use 2 x (b/c)  or 2 x (b^2/A) or  [(2b)^2] / 2A. It all gives the same number.

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It would seem the imminent death of ITUK has been greatly exaggerated.

Good line speed and pretty sharp in manoeuvres too.

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7 hours ago, erdb said:

Max, it doesn't matter how you calculate AR - whether you use span / mean chord or span^2 / area. It's the same thing once you replace area with span x mean chord.

When you double AR assuming a perfect seal under the sails, you can use 2 x (b/c)  or 2 x (b^2/A) or  [(2b)^2] / 2A. It all gives the same number.

It makes a huge difference when calculating the Di using the equations from @Basiliscus.  As per my original query, applying a doubling of the Span before or after squaring is quite crucial for balancing longitudinal forces etc, since I'm calculating these myself.

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2 minutes ago, MaxHugen said:

It makes a huge difference when calculating the Di using the equations from @Basiliscus.  As per my original query, applying a doubling of the Span before or after squaring is quite crucial for balancing longitudinal forces etc, since I'm calculating these myself.

They are mathematically the same thing. If you are getting different results, then there is an error somewhere in your calculations. Just put some numbers in the three versions I posted above. You should get the exact same AR with either of them.

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4 minutes ago, erdb said:

They are mathematically the same thing. If you are getting different results, then there is an error somewhere in your calculations. Just put some numbers in the three versions I posted above. You should get the exact same AR with either of them.

The equation I'm using is exactly as presented by B - which as he explained, does not use non-dimensional values such as AR, CL, etc:

Di = Lift2 / ( PI * e * 0.5 * Density_Air * Velocity2 * Span2 )     I have changed the Span part to (Span*2)2

Would be interesting to know how Vortex handles end-plating re Span when calculating Di - to double or not, or use a deduced  'factor' instead?

 

 

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9 hours ago, sosoomii said:

LOL. So? The physics hasn’t changed! 

No, but it's slightly easier to read and digest. :)

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26 minutes ago, MaxHugen said:

The equation I'm using is exactly as presented by B - which as he explained, does not use non-dimensional values such as AR, CL, etc:

Di = Lift2 / ( PI * e * 0.5 * Density_Air * Velocity2 * Span2 )     I have changed the Span part to (Span*2)2

Would be interesting to know how Vortex handles end-plating re Span when calculating Di - to double or not, or use a deduced  'factor' instead?

OK that's just written in a different form, but it's the same thing as calculating cdi first as cdi = cl^2 / PI * e * AR , and then Di = 0.5 * cdi * dens * A * v^2

So using your version, the (span*2)^2  is correct if you want to double the AR.

Vortex does handle end-plating, you have to specify if the wing is on a solid surface, but in addition to that and the AR, it also considers the shape of the planform (which is factored in as 'e' in the other equation). The advantage is that you can input the dimensions of the whole rig (jib and main), so I think it's more accurate than calculating induced drag separately for each sail.

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45 minutes ago, MaxHugen said:

The equation I'm using is exactly as presented by B - which as he explained, does not use non-dimensional values such as AR, CL, etc:

Di = Lift2 / ( PI * e * 0.5 * Density_Air * Velocity2 * Span2 )     I have changed the Span part to (Span*2)2

Would be interesting to know how Vortex handles end-plating re Span when calculating Di - to double or not, or use a deduced  'factor' instead?

 

 

image.png.b18443976df321c8b4657e19095b2af0.png

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If that's what they were aiming for with the boat noises (whalesong) they instead have exactly replicated a small cow being raped (as someone pointed out weeks ago). However they have the best looking hull.

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2 hours ago, fish7yu said:

 

Is there meant to be something new there?

Title of the vid suggests we are seeing the 3rd set of AM foils, but can't see shit cos of the fence.

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2 hours ago, jaysper said:

Is there meant to be something new there?

Title of the vid suggests we are seeing the 3rd set of AM foils, but can't see shit cos of the fence.

Yeah really stupid headline for this video. When I saw it I thought the exact same thing. 

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14 hours ago, buckdouger said:

well that was weird..

The real link (not the ad)

 

Does anyone else see Patriot's rudder foil cavitate, spray all over then she nosedives at the "end" of this race? Looks like they

lost rudder grip in the gybe. One of the risks of being overpowered downwind?

 

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5 hours ago, oysterhead said:

Does anyone else see Patriot's rudder foil cavitate, spray all over then she nosedives at the "end" of this race? Looks like they

lost rudder grip in the gybe. One of the risks of being overpowered downwind?

 

It happens when they come out of the jibe too hot with too much heel, but it's the opposite of nose dive. Assdive?? The same thing happened to them on the first day of sailing Patriot:

I think what happens is that normally they correct heel by turning off the wind, but if they come out too hot from the jibe, they can't correct it. It's probably a combination of ventilating the vertical blade of the rudder and maybe letting the sails out, which suddenly removes the forward pitch generated by the sails and that pushes down the transom overpowering the lift by the stabilator (which may also be ventilating). In this most recent video they actually did a great job preventing the jump that happened on the first day.

 

 

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