# Lexan thickness for deck hatch



## Alden68 (Mar 21, 2007)

I see Lexan marketed for use in deck hatch replacement with a thickness of .118". This seems incredibly thin and flismy to to me for a piece of hardware that could be stepped on. Is this the standard based on the strength of the material or am I looking at the wrong product for this application?


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## sailingdog (Mar 19, 2006)

Alden68-

I guess it depends on how big the hatch is. If the port is 3" x 10", like some of the opening ports you see on boats for ventilation purposes, then that might just be okay. If it is for a 23" x 23" hatch, ummm... you're gonna probably step through it. 

Size matters when it comes to deck hatch glazing thickness. The larger the opening, the thicker the glazing needs to be. Of course, some hatches have ribs or bars going across them and can get away with slightly lighter glazing materials, but that's an exception.


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## hellosailor (Apr 11, 2006)

Alden-
The key word is "marketed". Those guys will try to sell you anything. Like SD says, you've got to run some numbers, the size of the hatch, the loads you expect on it, etc. If the Lexan flexes every time you step on it, it probably will craze eventually. If the purpose is to have the lightest possible hatch glazing that will work for a couple of seasons of racing--it might be fine. If the purpose is to make sure a mast-mounted 20 foot spinnaker pole can't drop through...Maybe not.<G>


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## TSOJOURNER (Dec 16, 1999)

Might want to check with the folks at Select Plastics in Norwalk, CT. They do great work at a premium price......and they give free advice! 
Regards,
Red


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## Alden68 (Mar 21, 2007)

The hatch has two panels roughly 10 x 21 so they are fairly good size. Definitely not looking for weight reduction as my boat is essentially a sailing cow and I'm sure lexan won't speed her up!

Loewe - I'll look them up....they might be just the ticket.

Thanks.


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## sailingdog (Mar 19, 2006)

Given that Lewmar uses 3/8" plexiglass on their ports, which measure 20.5" x 15.375", as seen here. I would suggest that as a minimum thickness for your ports, which are roughly comparable in size.

I hope that helps...  BTW, that is from their Ocean series of hatches, which I believe are slightly lighter construction than their other hatches. Their Medium profile hatch has a glazing thickness of 1/2".


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## Alden68 (Mar 21, 2007)

Thanks SD. That makes a lot more sense than .118" !


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## sailingdog (Mar 19, 2006)

Glad to help...  That should give you a good ballpark of how thick a piece of Lexan you'll need. Lexan, IIRC, is a bit stronger than plexiglass or acrylic, so you should be pretty good with 3/8" Lexan... gives you a bit of extra strength.


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## Valiente (Jun 16, 2006)

I have 1/2" lexan throughbolted through steel frames on all my fixed ports and 1/4" tempered glass on the opening ports, which will take storm shutters. My forward hatch looks like it came off a tank. 0.118" or _*less than 1/8th of an inch*_ is a bad joke I wouldn't expect to see on a lake daysailer, never mind a forward hatch. A dropped can of beer from mouth level could conceivably take it out.


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## sailingdog (Mar 19, 2006)

Valiente-

Your boat is a tank.. so I'm not surprised... it is a steel boat as I recall...


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## TSOJOURNER (Dec 16, 1999)

Alden - were you looking at the Hunter replacement parts catalogue perchance ???


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## sailingdog (Mar 19, 2006)

Sailormann said:


> Alden - were you looking at the Hunter replacement parts catalogue perchance ???


Ooooh... so mean... funny... but mean...


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## Valiente (Jun 16, 2006)

sailingdog said:


> Valiente-
> 
> Your boat is a tank.. so I'm not surprised... it is a steel boat as I recall...


Yes, but my '70s racer (the boat I'm loaning out while we cruise) has 1/4" Lexan in the 19 x 19" Atkins and Hoyle fore hatch and 3/8" Lexan drop boards and 1/4" fixed portlights. 1/8" is fine for the glass over my knotmeter, but anywhere else? Not the way I sail.


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## Alden68 (Mar 21, 2007)

Who said anything about dropping a beer? That will get you keel-haued on my boat  Actually, the spongy core material will probably bounce the can right back into your hand....

West Marine and Defender both carry the .118" lexan marketed as hatch replacement material. Maybe they're in cahoots with Hunter....


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## sailingdog (Mar 19, 2006)

I think that material would work nicely for an instrument panel splash guard.. that's about it though... no point on using anything less than 1/4" if the hatch is in a place feet can stand on it...  

Valiente- 1/4" lexan sounds a bit light for a 19" x 19" hatch, but that's just me...


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## Hawkeye25 (Jun 2, 2005)

For years in the yacht repair business I have been replacing the cracked and scratched 1/4" plexiglas in most of the popular 20 x 20 inch deck hatches with tinted 3/8" plexi. At first, I bought raw stock and cut and drilled it myself, but I soon found that I could bring the old piece to a 'GOOD' plastic shop, and they would duplicate it in whatever material at whatever thickness I wanted. It even got so I would send the skeptical customers (those who think you're ripping them off) to the plastic people themselves, then call me when it's time to install it. I never met anyone who wasn't happy to see the thicker stock, but we all felt concern about the ease of scratching. I've heard that Lexan is more resistant to scratching, but is it available in tints? I've never asked and am retired now.


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## sailingdog (Mar 19, 2006)

I'm not sure which is more scratch resistant, as both are available with and without scratch-resistant coatings, and it would depend on how the glazing is coated IMHO. They seem to be about the same to me.

The main advantage of Plexiglass over Lexan is its superior UV resistance. Lexan tends to yellow in UV more than Acrylic IIRC. However, for serious use, like voyaging offshore, I would go with polycarbonate over acrylic, due to its superior strength and impact resistance.

Yes, polycarbonate is available in tints, as well as mirrored finishes. Usually only grey and bronze colors though.


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## hellosailor (Apr 11, 2006)

Valiente-
"0.118" or less than 1/8th of an inch is a bad joke I wouldn't expect to see on a lake daysailer, never mind a forward hatch. A dropped can of beer from mouth level could conceivably take it out."
Actually? No, I doubt that. You can take a sheet of 1/4" plexiglass and literally beat on it with a baseball bat, and you'll have to mount it very tightly and whale away to break through it. Lexan typically is 10x stronger than plexi (at 7x-8x the cost) so even 1/8" Lexan should take a similar whaling with a baseball bat. You'll probably have to fire that beer can out of a spud cannon, and make sure it is properly frozen first, in order to burst 1/8" Lexan.<G>
Or at least, send someone up the mast to drop it from the masthead!<G>


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## Valiente (Jun 16, 2006)

sailingdog said:


> I think that material would work nicely for an instrument panel splash guard.. that's about it though... no point on using anything less than 1/4" if the hatch is in a place feet can stand on it...
> 
> Valiente- 1/4" lexan sounds a bit light for a 19" x 19" hatch, but that's just me...


It could be 3/8"... and must be as I can stand on it and am a man of some substance.

It's in this family of hatches, anyway: XR Double Frame Cast Offshore Hatch

The new boat has 1/2" acrylic in a similar hatch.


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## Valiente (Jun 16, 2006)

hellosailor said:


> Valiente-
> "0.118" or less than 1/8th of an inch is a bad joke I wouldn't expect to see on a lake daysailer, never mind a forward hatch. A dropped can of beer from mouth level could conceivably take it out."
> Actually? No, I doubt that. You can take a sheet of 1/4" plexiglass and literally beat on it with a baseball bat, and you'll have to mount it very tightly and whale away to break through it. Lexan typically is 10x stronger than plexi (at 7x-8x the cost) so even 1/8" Lexan should take a similar whaling with a baseball bat. You'll probably have to fire that beer can out of a spud cannon, and make sure it is properly frozen first, in order to burst 1/8" Lexan.<G>
> Or at least, send someone up the mast to drop it from the masthead!<G>


Sure, I'll concede not many human-powered activities would destroy that hatch, but several tons of sea could. I have seen even Lake Ontario take out fixed portlights set into frames: the fellow in question switched to through-bolted smoked 1/2" Lexan that overlapped the old port. I have also seen a spin shackle in a strong wind crack a foredeck hatch into uselessness. It didn't penetrate, true, but just the whipping action was enough to spiderweb it.

Most of the heavy-weather books I've read have stressed that many current production boats have too large and too weak expanses of plexi/lexan/glass to stand a breaking wave, and that more and smaller portlights, fixed or opening, and provided with appropriate storm shutters, is still the way to go. But it's the rare boat that even has storm shutters, never mind a means to deploy them.


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## pmoyer (Oct 3, 2006)

Valiente said:


> Sure, I'll concede not many human-powered activities would destroy that hatch, but several tons of sea could. I have seen even Lake Ontario take out fixed portlights set into frames: the fellow in question switched to through-bolted smoked 1/2" Lexan that overlapped the old port.


FWIW, the Delphia 37, which is CE rated A1, uses 1/2" lexan in the skylights. When I was aboard at the Annapolis show, I asked about them. They're through-bolted onto stainless steel frames.

Cheers,
Phil


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## sailingdog (Mar 19, 2006)

Never underestimate what a flogging sheet or sail can do in high wind, especially if it is armed with a metal shackle.


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## pmoyer (Oct 3, 2006)

sailingdog said:


> Never underestimate what a flogging sheet or sail can do in high wind, especially if it is armed with a metal shackle.


AGREED! Even a cringle in moderate winds can draw blood if it hits you wrong (or right, I guess). I've never seen damage caused by a shackle or block whipped at the end of a line by a flogging sail in high winds. If it can break lexan ports (and I bet it can), I'd hate to think what it'd do to a person....

Cheers!


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## hellosailor (Apr 11, 2006)

V-
Several tons of seawater, sure, but that's the old question of "What is a bluewater boat?" isn't it?

I've seen widely varying calculations about the impact of green water and the damages it can do. I guess the first question is "How big was the wave you fell off? Or fell onto you?" and then after that, there's the move solve-able question of whether you treat the impact like concrete or somewhat less.<G> Using real simplified math isn't even really necessary, as a number of sources have said, your hatches really need to be equally strong as the deck or cabin house, whatever that may be. (And wood cabin houses have been stove in as well.)

Interesting flip side to Lexan glazing: On Amtrak trains, the windows are required to be bullet proof to a certain standard, to prevent hunting accidents (aka crazies in the woods). Some people actually Do worry about that. Funny thing though, the train walls themselves aren't built to the same standard, so you are safer being a target--behind the bullet resistant window. Hmmm.....


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## sailingdog (Mar 19, 2006)

hellosailor said:


> <g>Interesting flip side to Lexan glazing: On Amtrak trains, the windows are required to be bullet proof to a certain standard, to prevent hunting accidents (aka crazies in the woods). Some people actually Do worry about that. Funny thing though, the train walls themselves aren't built to the same standard, so you are safer being a target--behind the bullet resistant window. Hmmm.....


They don't want you to be able to see the shot coming...  
</g>


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## Valiente (Jun 16, 2006)

hellosailor said:


> V-
> Several tons of seawater, sure, but that's the old question of "What is a bluewater boat?" isn't it?


To a point. Boats are marketed to a false standard, really. To my mind, a "daysailer" shouldn't mean a weak boat, but a boat where the design favours speed and a certain response that makes for a "fun" motion: a sense of really being on a boat. That same motion in heavy weather (which can occur most places, not just the ocean) would be harsh and probably nauseating to the crew, but shouldn't mean the boat can't take a few wave hits.

The majority of production boats are geared to the "coastal" market, which is in reality the "sit at dock unless it's a flat sea with 10-15 knots" market...present company excepted. The same issues with motion arise, because a flat bottomed fin keeler is going to have a sharp motion. But "coastal" waters can be signficantly more lumpy and subject to tide rips and short bursts of squally weather than the open ocean in many cases, and I feel that when design trumps safety and excessive cabin windage, lined with thin portlights, makes for a certain measure of instability, then we have a situation in which recreational sailors can get in trouble.

I am an advocate of the right boat in the right conditions, but I'm more of an advocate of the right crew for the right conditions. You don't put a minivan in an F1 race not just because it's dangerous and inappropriate, but also because it would scare the crap out of the minivan's crew just the same way as getting a punched in saloon window (I won't call them "port lights" when they are bigger than a TV screen) would frighten a crew into irrationality.

Remember _Satori_? Portlights stayed intact! SATORI and the Perfect Storm


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## sailingdog (Mar 19, 2006)

Yes, and Satori was a fairly heavily built Westsail 32, which is a bluewater boat. I doubt that a 32' Hunter, Bendytoy or Jeanneau would have fared as well. 

Crew preparation is a key piece of being able to handle bad weather. However, it is not the only factor. A good crew in a bad boat is almost as badly off as a bad crew in a good boat. The reason I say almost is that the good crew can often make more of a bad boat, than the bad crew can generally screw up a good boat.


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## pmoyer (Oct 3, 2006)

*So back to the question...*

What thickness would we consider "appropriate" for a Lexan deck hatch? Let's set the dimensions at 22x22 inches, just so we're talking about the same thing.

BTW, a 48x96 inch sheet of .5" clear, uncoated Lexan, from Professional Plastics, is $614.82. Not cheap stuff....

Cheers!


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## sailingdog (Mar 19, 2006)

I would go with 3/8" Lexan for a hatch that is 22" x 22" as a minimum. You could go up to 7/16" Lexan, but it would be a bit overkill IMHO.


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## hellosailor (Apr 11, 2006)

Phil-
I know I've seen better numbers but offhand can't find them. And if you search for something like "impact of green water" you'll find lots of articles referring to computer simulations and complexity, but no simple answer.

Ballpark? Let's pretend the water is concrete and a block of it is falling on your hatch, i.e. the top of a wave 40' up just broke and is coming down at you. 

And force = mass x acceleration, i.e. impact Force = m x a. 

The unbalanced force F is measured in newtons (N) and that will be the impact. The mass m is measured in kilograms (kg), one cubic foot of seawater is about 35 pounds or 16kg.

Beyond that, I'm less sure of how to do the math for the acceleration of the falling water. Or, how much you want to allow for the glazing getting weaker perhaps as it gets older, crazes, or is subject to point loads because of the way the framing is done, the deck twisting or torquing it perhaps, etc.

I suspect that when new 1/4" Lexan of many grades is sufficient, but 1/2" seems to be more commonly used, perhaps because builders know that if someone is looking for Lexan in the first place, they'd rather pay for the safety margin from excess thickness?


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## Sialia (Feb 14, 2006)

Cast Acrylic was recommended to me over lexan. I used 1/2 inch thickness. It's not cheap!


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## Valiente (Jun 16, 2006)

sailingdog said:


> Crew preparation is a key piece of being able to handle bad weather. However, it is not the only factor. A good crew in a bad boat is almost as badly off as a bad crew in a good boat. The reason I say almost is that the good crew can often make more of a bad boat, than the bad crew can generally screw up a good boat.


A good crew on a bad boat can judge whether they are going to have to save themselves (if possible) or if they are going to have to solicit rescue (if possible or available). But unless they do deliveries, good crew usually have the option to avoid bad boats.

Bad crew can't recognize or deal with a good boat because they panic and resemble rats in cages in a room full of cats. The cage is perceived as a trap as opposed to the only protection available from the damn cats.

_Satori _was a special case, but instructive. Conditions were bad enough to put the fear into even experienced crew, but no matter what the experience and skill and _knowledge of his own vessel's endurance _ her skipper had, he either couldn't convey his confidence or, let's face it, command his crew when things got rough. It's not always possible to throughly vet one's crew, but I suspect he regrets that he was perhaps not as picky as he might have been in this case. For whatever reason, he did not inspire in his crew a belief that conditions were survivable, and they panicked.

I wasn't there and can't say if Horatio Nelson could have done that, but other boats have been in even worse conditions without having a form of mutiny added to their woes. I will say that this story has probably kept the selling price of old Wetsnails well above what it otherwise might be!


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## sailingdog (Mar 19, 2006)

HS-

I hate to break it to you, but seawater, at the surface, on average weighs 1027 kg/m3, or just over 64.1 lbs per cubic foot. That's gonna change your calculations quite a bit... 

While 1/2" is really nice, I like the 3/8" because it does have a bit of safety margin built-in, and is far more reasonably priced than the 1/2" Lexan is. 

Also, lexan tends to not shatter, but cold form, when exposed to repeated heavy impacts... so no shrapnel and a much more controlled form of failure. Plexiglass will shatter IIRC.


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## dustdevil38 (Jan 3, 2005)

*try ebay*

Hi-

I've found both 1/2 and 3/8 Lexan on Ebay for good prices. You just have to be patient. My local plastic supplier didn't carry these thicknesses and required a full-sheet special order. Abrasion resistant lexan, which is desireable but not necessary, is referred to as Margard, AR, or MR10. One thing to note: 3/8 and above is hard to bend. If your hatch has a lot of camber (many older OEM hatches do), you may have trouble with the 3/8,


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## Alden68 (Mar 21, 2007)

I have discussed the project with select plastics of CT and they recommend a min. of 3/8". Seems like a good thickness for me. If a 40' wave is about to break on my boat I don't care what it weighs or how thick my hatch is........I'm in the wrong place at the wrong time....with the wrong boat, the wrong ego, the wrong lifevest, the wrong beer cooler, the wrong jack lines, etc.......

I'm not fishing for Ophelia Crabs for Christ's sake!!!!!


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## sailingdog (Mar 19, 2006)

Alden-

You've got that right... try to avoid 40' breaking waves...  The 1/2" is about 50% more than the 3/8" from what I've seen.


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## TSOJOURNER (Dec 16, 1999)

*1/2" Cast Acrylic*



Sialia said:


> Cast Acrylic was recommended to me over lexan. I used 1/2 inch thickness. It's not cheap!


Cast acrylic should _always _be used, period. Not only is it stronger for all this bluewater sailing everyone is talking about but cast acrylic fairs much better when it comes to crazing prevention. A good sheet of cast acrylic will easily last 12-15 years with proper care without crazing. As far as thickness goes, for offshore hatches the standard should be 1/2", its that simple. Anything less than 1/2" cast acrylic on a forward hatch in bluewater is to risky for my family.


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## hellosailor (Apr 11, 2006)

" A good sheet of cast acrylic "
That would be a terrible expense. Casting (acrylic or polycarbonate) means pouring the liquified resin into a mold and making something of it. Using that process to make simple flat SHEETS is terribly slow and expensive, compared to an extrusion machine which can turn out sheets that are essentially identical to cast ones--but made without the time and expense of molds and molding. The extrusion machine is going to use pretty much the same resins, heated in pretty much the same way, just "poured" continuously instead of cast into a mold.

If you've got a 3-D shape, like a window with a rim on it, or a curved surface, casting is great, but I've never heard anyone recommend using CAST resins for flat sheets. That's like hand-made toothpicks, each whittled from a single tree: A bit excessive, to me.

(Just one man's opinion, but the nice folks who own the Lexan trademark at GE's "Structured plastics" division, sold me on it. Either you buy pellets and cast them, or you buy "structured" plastics, meaning, already formed into sheets and other shapes, ready to cut and mount.)


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## TSOJOURNER (Dec 16, 1999)

hellosailor said:


> " A good sheet of cast acrylic "
> That would be a terrible expense. Casting (acrylic or polycarbonate) means pouring the liquified resin into a mold and making something of it. Using that process to make simple flat SHEETS is terribly slow and expensive, compared to an extrusion machine which can turn out sheets that are essentially identical to cast ones--but made without the time and expense of molds and molding. The extrusion machine is going to use pretty much the same resins, heated in pretty much the same way, just "poured" continuously instead of cast into a mold.


Its interesting that some pieces of hardware on a boat get the full treatment, but that one of the most important touchpoints between you and the water is ignored. Cast acrylic is more expensive, and of course the kind folks over at Lexan are going to sell you on an extruded product. Extruded acrylic may be cheaper in the short term, but when you have to replace it 2 or even 3 times more often than cast acrylic, the disadvantages suddenly become apparent.

The costs associated with producing cast acrylic directly translates into a superior product. The extra strength and durability of a cast acrylic does not exclusively come from different resins or temperatures (though they play a critical role), but from the way that the sheet is allowed to cool and set up. Extruded products are cooled rapidly, producing very little organization at the molecular level within the acrylic. Cast arcylic, on the other hand, cools much more slowly and naturally and allows for a kind of molecular lattice to set up which adds strength and durability.

I can understand the prohibitive costs that an individual consumer would experience by going out and getting their own cast acrylic sheet. However, if you were to go to a quality hatch manufacturer that uses cast acrylic they would be able to sell you exactly what you need at a fraction of the individual cost.

I am afraid that "essentially identical" leaves out some important details that really should be considered by a responsible sailor.

Also while on this topic of cast vs. extruded, I would like to point out that there is a major difference between many hatch frames. Most are now extruded with less-than-marine-grade aluminum. The extrusion process may be much cheaper for the lids and bodies of a hatch, but this is vastly outweighed by the number of years a true cast Almag-35 hatch/port will last.

For a truly strong, durable, reliable and ocean worthy hatch, these would be my required specs;

1/2" cast acrylic
Cast Almag-35 lids, bases, handles
All 316 stainless steel hardware with corrosion blocker

There are hatches available on the market with these features set as a standard. Initial cost may not be what you would think they are and amortized over the 15 to 25 lifespan it becomes very advantagous to go with qulaity over price-point.


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