LionessRacing

Light Air Polars: How low do you go?

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The US SAILING VPP polars are 6 kt increments from 0. 

I find that I am doing quite a bit of sailing in < 6, and that there are distinct differences in how Lioness seems to perform in < 2, 2 -4 and 4-6 especially off wind.  

Both B&G and Exp interpolate, but the 0-6 range is essentially an extrapolation from the singularity at 0. 

What's the reasonable best practice in setting up polar tables for lighter winds? 

Given that force is proportional to square of wind speed, an argument could be made to take data for 2, 4, 8 and let that bracket./calibrate the 6 kt VPP reading. 

 

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I installed the Yacht Devices - Voyage Recorder -> convert the native data into Excel format (download converter from website) and do the analysis using standard Excel features.

 

image.png.98a3406c72ce6f556088e06721f0e24c.png

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34 minutes ago, bgytr said:

What kinda boat?

<--- Mine's listed in the signature (1958 CCA design full keel centerboard yawl), yours would probably be different. 

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4 minutes ago, LionessRacing said:

Mine's listed in the signature (1958 CCA designed full keel centerboard yawl), yours would probably be different. 

Different? The signature or the boat?  I don't see any boat type in a signature but did a search online and got a Bermuda 40.  Is that your boat?

If so, and the wind is below 6, you ain't goin nowhere.  Kidding aside, plot the polar data you have in excel and extrapolate some curves.  Likely will be close enought for routing purposes.  But for targets while sailing, stuff gets too variable and unstable below 6 kts true, especially in a slower heavy boat.  Just sail her as best you can.

If it was a lightweight rocket like a TP52 or larger where it makes its own wind, VPP polars would be a bit more accurate at lower speed.

My guess would be for your polars, you're gonna go about 45% of the true wind speed in the low range, maybe a bit less, for just about all true wind angles between 48 to about 120.  Maybe up a couple percent in the beam reaching range.  Drop to about 30 pct true wind speed dead downwind and smooth the curve. Probably will be close enough for planning.

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1 minute ago, bgytr said:

don't see any boat type in a signature

 
 
 
 
Quote

SV "LIoness"

1962 Bermuda 40 Classic Yawl

hull #24

That boat type... 

And we do make our own wind going up in > 4 kts. You just never want to have to tack... 

Going down in < 2 kts is an exercise in patience and meditation and finding 1/10 kts of better current

 

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Regardless of boat, light air sailing requires so much more sensitivity to keep the boat moving what practical use are polars except a distraction?

If a below deck navigator pops his head out of the hatch to tell everyone on deck they’re 10% below theoretical and basically rely on data that’s at the threshold of instrument sensitivity - throw them over board. 

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I don’t build my polars out below 4 knots tws. I find it hard to get good data below 6 knots on the bay, there is always current mixed into the data. 

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Boat speed and wind speed are mostly just noise in those ranges and without instrument data, the polars are a waste of time.

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What moonduster said. There's a reason why the VPP's don't create the polars below 6 kts. ORR-ez add a "v. light" rating, but the 4kts is really just an interpolation and aiui no real calcs are done at that speed because they are 'meaningless.'

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Below 6 knots TWS is actually the most interesting and dynamic portion of the whole displacement sailboat performance problem. Sadly, most race committies summarily throw it out and most sailors show zero interest down there. I could take you through the maths about it but most people don't give a shit about it.

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46 minutes ago, fastyacht said:

Below 6 knots TWS is actually the most interesting and dynamic portion of the whole displacement sailboat performance problem. Sadly, most race committies summarily throw it out and most sailors show zero interest down there. I could take you through the maths about it but most people don't give a shit about it.

In some parts of the country, throwing out racing below 6 knots means throwing out racing. My boat does ok in those conditions, depending on the time of year/actual weather conditions. Gradients can make it difficult if I'm seeing 6 kts at the masthead but it's never getting down to the surface because our rig is shorter than most of the other 30'+ boats in our class, and it's only a 108% jib. I've always maintained it's harder to be a good light air sailor than a heavy air sailor, if for no other reason the enormous amount of patience involved.

I can remember one deathless Fall Offsoundings Saturday where the only reason we didn't withdraw was because the GPS showed us making 1 knot over ground toward the finish. It was definitely a race of attrition though. After about an hour and a half of zero breeze, one of my crew opened a bag of potato chips and I nearly exploded it was so loud and distracting. 15 minutes later we started to get zephyrs (named for the greek god of false hopes and dashed promises) and the crew was elated that we had exceeded 2 kts boatspeed through the water, for the first time since about a half hour after the start. Wind built after that and another boat in our class managed to beat the time limit so we had time to finish. Ended up pretty good for us overall, ultimately, but man was that a grind. My neck was more sore from that than from any 25 knot downwind blast.

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1 hour ago, Moonduster said:

Boat speed and wind speed are mostly just noise in those ranges and without instrument data, the polars are a waste of time.

Yes, and against proficient opponents the advantages of sailing to the polars are overwhelmed by hunting for pressure, keeping speed on, offense, defense,, et cetra.

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I keep an eye at VMG. With my old Bristol 43.3, I'd try to build some speed, find some pressure and head down and then bring her back up. I'm happy if I can do 40-45% of the apparent wind at that speed range.  I once did  a regatta on my old Flying Scot. I had a great sailor who was a sail maker crewing with me and my 5 yr old son. It was drifting conditions on the Navasink River in NJ. He just kept on saying point the bow at the mark... We ended up winning.

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Having a polar percentage in a drifter is not useful;

having a Target wind angle to optimize VMG is, and recognizing that it will be very dynamic as the wind speed (and apparent direction) will likely be changing faster than the boat. 

 

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3 minutes ago, LionessRacing said:

Having a polar percentage in a drifter is not useful;

having a Target wind angle to optimize VMG is, and recognizing that it will be very dynamic as the wind speed (and apparent direction) will likely be changing faster than the boat. 

 

There is too much hysteresis to make trying to sail to some specific angle useful. The moment you lock your course you slow down. It must needs be dynamic sailing to vmg. The closest parallel is 18 foot skiffs in 30 kts. Just not as wet and as fast. Same dynamics of apparent wind apply.

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3 hours ago, fastyacht said:

Below 6 knots TWS is actually the most interesting and dynamic portion of the whole displacement sailboat performance problem. Sadly, most race committies summarily throw it out and most sailors show zero interest down there. I could take you through the maths about it but most people don't give a shit about it.

We all too often are racing in < 6 kts average, and occasionally that turns into a "typical" SF afternoon thermal, at 1200-1300 in the summer as the Central Valley heats up.  

On weeknights it's usually the fading breeze against the tide... 

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Just now, fastyacht said:

There is too much hysteresis to make trying to sail to some specific angle useful. The moment you lock your course you slow down. It must needs be dynamic sailing to vmg. The closest parallel is 18 foot skiffs in 30 kts. Just not as wet and as fast. Same dynamics of apparent wind apply.

Understand hysteresis and dynamic optima, hence the question of how much to heat up vs drive down with a boat that is in a gentle term "stately" in it's response. 

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In a heavy boat in the light stuff, I keep the rudder as still and straight as possible.  Need good trimmers, constant lead and sheet adjustment on the headsail, same on the main vang, traveler and sheet.  Upwind I take a course roughly 5 or so degrees off tight upwind and play the sail trim.  Only use the rudder if absolutely necessary.

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Target wind angle to optimize VMG

But with no AWA, AWS and boat speed, you have no VMG.

At this corner of the envelope, one's instruments are worthless and other than perhaps depth are best turned off - they provide no information.

Those who excel in drifters keep their heads out of the boat, minimize wetted surface, pitching and control inputs and work like mad at sheeting angles, trim and the traveling the shortest possible course to the next mark.

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Throw out any polar information. If you have instruments chances are they are not calibrated to do much good from tack to tack. If your reaching and your kites flies w/o much shake, just sail your course. If running, sail the angle that fills the kite w/o sailing too high just to make yourself feel good. The trimmer is actually driving the boat telling you when he needs heat or you can soak. Most club racers just reach around the course downwind. Try this and you'll usually make large gains on your competition.

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12 hours ago, bgytr said:

Different? The signature or the boat?  I don't see any boat type in a signature but did a search online and got a Bermuda 40.  Is that your boat?

If so, and the wind is below 6, you ain't goin nowhere.  Kidding aside, plot the polar data you have in excel and extrapolate some curves.  Likely will be close enought for routing purposes.  But for targets while sailing, stuff gets too variable and unstable below 6 kts true, especially in a slower heavy boat.  Just sail her as best you can.

If it was a lightweight rocket like a TP52 or larger where it makes its own wind, VPP polars would be a bit more accurate at lower speed.

My guess would be for your polars, you're gonna go about 45% of the true wind speed in the low range, maybe a bit less, for just about all true wind angles between 48 to about 120.  Maybe up a couple percent in the beam reaching range.  Drop to about 30 pct true wind speed dead downwind and smooth the curve. Probably will be close enough for planning.

Never seen a polar diagram for below 6 knots.  Instruments would be all over the place and useless.  TWA and TWS are pretty useless anyway unless you have a B&G rep on your boat full time.

TP52 polars:  Downhill basically put the bow up and keep the apparent wind well ahead of 90° and the boat pressured up.   Go wind hunting. NEVER sail deep.  First boat to the next puff is gone.

Advice here for the Bermuda 40 seems about right.  

 

 

 

Screen Shot 2020-02-03 at 5.33.49 PM.png

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26 minutes ago, Left Shift said:

Never seen a polar diagram for below 6 knots.  Instruments would be all over the place and useless.  TWA and TWS are pretty useless anyway unless you have a B&G rep on your boat full time.

TP52 polars:  Downhill basically put the bow up and keep the apparent wind well ahead of 90° and the boat pressured up.   Go wind hunting. NEVER sail deep.  First boat to the next puff is gone.

Advice here for the Bermuda 40 seems about right.  

 

 

 

Screen Shot 2020-02-03 at 5.33.49 PM.png

I used to nav on a tp52, got pretty good at the instruments cal and could get em real close on the fly using expedition with the tablet on the rail.  I forget that stuff now, if I don't do that stuff all the time I have to relearn it.

We used to steer offwind using the TWA and target TWA.  Worked pretty well, seemed to be the most stable steering guide. The main feedback is the chute trimmer though, the numbers are a secondary guide. Surprising how wide the TWA is even with the apparent forward of the beam cuz your going so fast.

I filled in the polars at lighter wind speeds using data recording and analysis between races.  

I've had polars computed at 4 knots for distance races for planning.  In a tp52, AWS can be 10+ in 5 to 6 TWS, plenty adequate for instrument data if you stay on top of the cal.

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3 hours ago, duncan (the other one) said:

Stop worrying about if the boat is at some magic predicted speed, and worry more about keeping it moving and in the patches of stronger breeze.

...as the entire fleet sails whatever angle “feels fast” and in the wrong direction.

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I've sailed both ends of the polar spectrum.  A Star boat loves to sail deep for best VMG. Yes, when very light, one does beam reach and tack downwind a lot.

On the sled, in most winds we beam reached and tacked downwind.  It was a rare day where we pulled the pole back and started to run (20 knots true +). As we sailed with many Star sailors on this boat, we struggled greatly to beam reach and lost a ton of races as a result. Once I "got it" I would hound the shit out of everyone to get the pole on the headstay and just go fast which is what sleds love.

Learn your boat, find your sweet spots and memorize them.

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On 2/3/2020 at 6:42 PM, bgytr said:

I used to nav on a tp52, got pretty good at the instruments cal and could get em real close on the fly using expedition with the tablet on the rail.  I forget that stuff now, if I don't do that stuff all the time I have to relearn it.

We used to steer offwind using the TWA and target TWA.  Worked pretty well, seemed to be the most stable steering guide. The main feedback is the chute trimmer though, the numbers are a secondary guide. Surprising how wide the TWA is even with the apparent forward of the beam cuz your going so fast.

I filled in the polars at lighter wind speeds using data recording and analysis between races.  

I've had polars computed at 4 knots for distance races for planning.  In a tp52, AWS can be 10+ in 5 to 6 TWS, plenty adequate for instrument data if you stay on top of the cal.

Several things jump out from that polar chart.

One is the huge difference in the angle between the sweet spot (the tiny little dot) on the AWA and the sweet spot on the TWA side of the polar.  Sailing with an AWA of 70°-75° in 6 knots can get you downhill quite nicely at a 140° TWA.

The second is how flat the curve is in the lower wind speeds for the AWA and the TWA.  So there may be options to range high or low strategically.

The third is the large changes as wind increases/decreases in the AWA for the best VMG while the TWA changes comparatively little.  Which supports your comment about using the TWAs for stable steering guide.  But that's with a skilled person working the calibration problem in real time.  As you say, the spin trimmer gives more instantaneous information.

For me, an educated, head-out-of-the-boat, seat of the pants in light air is almost always faster than instrument flying.

 

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Lioness, you cannot see your signature in Chrome on Android, or anyone else for that matter...

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In a practical sense I agree with many of the things said above e.g. focus on keeping the boat moving.

In a more academic sense, the Beaufort Scale has three "gears" below 6 knots: 0-1 knot, 1-3 knots, 4-6 knots - why not use those as a guide? 

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12 hours ago, Left Shift said:

Several things jump out from that polar chart.

One is the huge difference in the angle between the sweet spot (the tiny little dot) on the AWA and the sweet spot on the TWA side of the polar.  Sailing with an AWA of 70°-75° in 6 knots can get you downhill quite nicely at a 140° TWA.

The second is how flat the curve is in the lower wind speeds for the AWA and the TWA.  So there may be options to range high or low strategically.

The third is the large changes as wind increases/decreases in the AWA for the best VMG while the TWA changes comparatively little.  Which supports your comment about using the TWAs for stable steering guide.  But that's with a skilled person working the calibration problem in real time.  As you say, the spin trimmer gives more instantaneous information.

For me, an educated, head-out-of-the-boat, seat of the pants in light air is almost always faster than instrument flying.

 

Ya the TWA offwind seems a fairly wide window with variable wind speed and a pretty good guide in my experience, granted, the cal needs to be good.  I've had the good fortune to sail with great trimmers and helmsmen who understand the dynamics of the situation. They are able to process all of the input- TWA, target TWA, TWS, BS, HDG and the rate of change of the dials as well as the feel of the boat and keep it rolling well.  It's really cool when you get em all dialed in together "in the zone".

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6 hours ago, sshow bob said:

Lioness, you cannot see your signature in Chrome on Android, or anyone else for that matter...

FWIW;

 

I use Chrome on Win10 and it's there... image.thumb.png.774e21e4e739691988449b5c8c8cefaf.png

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13 minutes ago, bgytr said:

Ya the TWA offwind seems a fairly wide window with variable wind speed and a pretty good guide in my experience, granted, the cal needs to be good.  I've had the good fortune to sail with great trimmers and helmsmen who understand the dynamics of the situation. They are able to process all of the input- TWA, target TWA, TWS, BS, HDG and the rate of change of the dials as well as the feel of the boat and keep it rolling well.  It's really cool when you get em all dialed in together "in the zone".

The rate of change of the digital data for sure can trip drivers up if they are focused on the instruments.  What appears on the instrument is blended in what happened 30 seconds ago based on the averaging period on "true" calculations, which are second or third level integrations by the software.  (You know this, but writing here for the OP).  So the driver/trimmer combo has to start to stop a trend as soon as it shows up.

Hardest driving I've ever done was on a moonless, clouded-over night 1,000 miles of shore with puffy winds and lumpy water.  So dark that you couldn't see the white kite or who was in the cockpit with you.  With only instruments to go by, the temptation to over correct or to get lost in the video game of balancing course, TWA, TWS, BS was huge.  

 

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4 minutes ago, LionessRacing said:

FWIW;

 

I use Chrome on Win10 and it's there... image.thumb.png.774e21e4e739691988449b5c8c8cefaf.png

In Chrome on Android, not in Chrome and on Android. 

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3 minutes ago, LionessRacing said:

FWIW;

 

I use Chrome on Win10 and it's there... 

Yep - I see the signatures on Chrome on Windows devices (and Mac), I think because I get desktop display as my default.  On my Android personal phone, iPhone work phone, and iPad, the browsers default to showing mobile mode, and the signatures go away (together with post counts, ratings, buttons to mark forums read, and other stuff).  I wasn't harshing you with this, just explaining why your conversation had gone off track with that other poster.

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20 minutes ago, bgytr said:

Ya the TWA offwind seems a fairly wide window with variable wind speed and a pretty good guide in my experience, granted, the cal needs to be good.  I've had the good fortune to sail with great trimmers and helmsmen who understand the dynamics of the situation. They are able to process all of the input- TWA, target TWA, TWS, BS, HDG and the rate of change of the dials as well as the feel of the boat and keep it rolling well.  It's really cool when you get em all dialed in together "in the zone".

The training of the helm to feel the boat, and the trimmers to react to various winds takes time, especially when you have low winds and heavy displacement. Gauges help to alert you to changes and to assess best available performance.

Noting that the AWS increased and thus the AWA will decrease and the jib needs gentle trimming is an alternative to getting them to understand tell tales that are not responsive in light airs and often stick etc. 

Noting that the best VMG for a drifter may be fairly high is easy, deciding intuitively what that course/angle should be is harder, the slope of VMG vs angle is steep in some regimes. 

Appreciate the answers, I'll try to get data sets and see if they can be extracted for 3 kts first and if that's sensible a further refinement to 2 & 4 though at 2 TWS my BSP tends to read Zero.... 

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Lioness, you cannot see your signature in Chrome on Android, or anyone else for that matter...

Maybe you have signature view turned off? Doesn't everyone?

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3 hours ago, Left Shift said:

The rate of change of the digital data for sure can trip drivers up if they are focused on the instruments.  What appears on the instrument is blended in what happened 30 seconds ago based on the averaging period on "true" calculations, which are second or third level integrations by the software.  (You know this, but writing here for the OP).  So the driver/trimmer combo has to start to stop a trend as soon as it shows up.

Hardest driving I've ever done was on a moonless, clouded-over night 1,000 miles of shore with puffy winds and lumpy water.  So dark that you couldn't see the white kite or who was in the cockpit with you.  With only instruments to go by, the temptation to over correct or to get lost in the video game of balancing course, TWA, TWS, BS was huge.  

 

I hear ya... One Bermuda race years ago at about 2am the owner was driving.  Light air, exiting the stream, left over slop... The owner steered a complete circle, everyone on deck was like wtf!   But didn't want to yell at the boss.  We bout peed our pants laughing about that after a few dark and stormies at the finish line.

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12 minutes ago, bgytr said:

I hear ya... One Bermuda race years ago at about 2am the owner was driving.  Light air, exiting the stream, left over slop... The owner steered a complete circle, everyone on deck was like wtf!   But didn't want to yell at the boss.  We bout peed our pants laughing about that after a few dark and stormies at the finish line.

Sometime you have to force yourself not to hunt the apparent wind numbers. 

Thread drift alert....On a light, light Transpac, I'm 60% asleep down below, also about 2 a.m., and I hear the guys on deck say "Now what do we do?"  Not what you really want to hear on a 50'er when you're all cozy.  I jump up on deck and they've got the kite blown through the foretriangle, aiming back at LA and the helm hard over, going nowhere.  

I say, let's try this before we wake anybody else up, spin the wheel the other way, the boat tacks, bears off, jibes, main swings over, kite fills like it wants to help and we start moving nicely.  Never touched the pole. I point west and say "Go that way" and go back to sleep.  

Owner and off-watch never woke up.  Mai-Tais in my case.

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53 minutes ago, Left Shift said:

Sometime you have to force yourself not to hunt the apparent wind numbers. 

Thread drift alert....On a light, light Transpac, I'm 60% asleep down below, also about 2 a.m., and I hear the guys on deck say "Now what do we do?"  Not what you really want to hear on a 50'er when you're all cozy.  I jump up on deck and they've got the kite blown through the foretriangle, aiming back at LA and the helm hard over, going nowhere.  

I say, let's try this before we wake anybody else up, spin the wheel the other way, the boat tacks, bears off, jibes, main swings over, kite fills like it wants to help and we start moving nicely.  Never touched the pole. I point west and say "Go that way" and go back to sleep.  

Owner and off-watch never woke up.  Mai-Tais in my case.

A mai tai sounds pretty damn good at the moment...

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Lot of super stars around here. B)

Talking polars, let me ask a stupid question: How good is your autopilot doing in light air <6kn?

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5 hours ago, Mordoc said:

Lot of super stars around here. B)

Talking polars, let me ask a stupid question: How good is your autopilot doing in light air <6kn?

as long as my boat is making 2+ knots, the AP seems to do just fine. below that, it screams a lot.

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On 2/4/2020 at 5:17 AM, fastyacht said:

Below 6 knots TWS is actually the most interesting and dynamic portion of the whole displacement sailboat performance problem. Sadly, most race committies summarily throw it out and most sailors show zero interest down there. I could take you through the maths about it but most people don't give a shit about it.

This is one of my greatest frustrations - too many owners throw up the "but my boat just can't move in those conditions" excuse, when in fact all they need to do is pay attention and tell their main trimmer to back off.

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