# Lexan VS Acrylic



## weephee (Oct 25, 2008)

I am replacing the smoked cover on my hatch. I don't know what material it is but I do have a piece of smoked acrylic available to me. Area is 20 inches x 20 inches with two parallel support pieces running 5 inches apart under it. Is it OK to use the acrylic or should I be looking for a piece of Lexan. Thanks


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## sailingdog (Mar 19, 2006)

Most hatches use cast acrylic, not lexan, with the exception of a single line of Bomar hatches IIRC. What kind of port is it? How thick is the piece you have?


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## JohnRPollard (Mar 26, 2007)

Our Bomar hatches are polycarbonate (Lexan). Most other hatches I've worked on were too. 

Lexan is stronger but less UV resistant than acrylic. Acylic is often used for smaller portlights, whereas Lexan is preferred because of its strength for larger areas like hatches. 

For a 20"x20" opening, I'd use Lexan/polycarbonate, not acrylic.


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## sailingdog (Mar 19, 2006)

JRP-

I doubt that... Most hatches are cast acrylic because polycarbonate foreshortens when it flexes under impact, making it very unlikely to remain sealed. If you check with Lewmar, one of the larger hatch producers, all of their specs mention the thickness of the acrylic... not lexan or polycarbonate.


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## PeterSailer (Mar 20, 2010)

I don't know about acrylic but Lexan is very easy to scratch...


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## JohnRPollard (Mar 26, 2007)

SD,

Has that always been the case? I guess I've worked on a few hatches in the past, all of them older and in need of work due to UV degradation. I recall them being polycarbonate.

I also recall when researching a material to use for our portlight lens-replacements (in our previous boat), that acrylic was considered a good fit for portlights, but that polycarbonate was recommended for hatches or larger deadlights.

Maybe there has been a shift in newer hatches to acrylic, or is it that some of the "value" oriented designs use this less expensive material for the lens?

Here's one that is similar to ours, which uses polycarbonate:

BOMAR CAST ALUMINUM HATCH # 139L. 24 " X 24" BLACK


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## sailingdog (Mar 19, 2006)

acrylic- more scratch and uv resistant

Lexan- more impact resistant


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## sailingdog (Mar 19, 2006)

JohnRPollard said:


> SD,
> 
> Has that always been the case? I guess I've worked on a few hatches in the past, all of them older and in need of work due to UV degradation. I recall them being polycarbonate.
> 
> ...


Note the reinforcing bars-they're to prevent the polycarbonate from flexing enough to break the seal. Yours are the one kind made with polycarbonate. All the others are acrylic.


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## erps (Aug 2, 2006)

Which one bends with some heat? I've seen some do-it yourself projects using one of those materials. It looked easy to cut and easy to shape but I can never remember which one.


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## sailingdog (Mar 19, 2006)

Both will bend with heat. Both are fairly easy to cut and shape.


erps said:


> Which one bends with some heat? I've seen some do-it yourself projects using one of those materials. It looked easy to cut and easy to shape but I can never remember which one.


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## weephee (Oct 25, 2008)

Thank you for all the replies. I used the word acrylic which I assumed is the same thing as plexiglass. Is this correct. The material I am replacing is 3/16 inches thick and because of the parallel supports the plastic is supported about every 6 x 20 inches. I would show a picture but the hatch is being powder coated so I don't have it with me right now. One more thing if I may. The original was screwed on around the perimeter with a screw every 3 inches. With todays adhesives, can I glue it down onto the aluminum frame instead. There is a 1/4 inch groove or channel running around the inner perimeter of the frame to hold a sealant. Less screws, less places to leak. Thanks


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## sailingdog (Mar 19, 2006)

Yes, plexiglas is a tradename for Acrylic plastic. YOu should be able to hold it in place using Dow 795 structural silicone adhesive.


weephee said:


> Thank you for all the replies. I used the word acrylic which I assumed is the same thing as plexiglass. Is this correct. The material I am replacing is 3/16 inches thick and because of the parallel supports the plastic is supported about every 6 x 20 inches. I would show a picture but the hatch is being powder coated so I don't have it with me right now. One more thing if I may. The original was screwed on around the perimeter with a screw every 3 inches. With todays adhesives, can I glue it down onto the aluminum frame instead. There is a 1/4 inch groove or channel running around the inner perimeter of the frame to hold a sealant. Less screws, less places to leak. Thanks


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## Maine Sail (Jan 6, 2003)

weephee said:


> Thank you for all the replies. I used the word acrylic which I assumed is the same thing as plexiglass. Is this correct. The material I am replacing is 3/16 inches thick and because of the parallel supports the plastic is supported about every 6 x 20 inches. I would show a picture but the hatch is being powder coated so I don't have it with me right now. One more thing if I may. The original was screwed on around the perimeter with a screw every 3 inches. With todays adhesives, can I glue it down onto the aluminum frame instead. There is a 1/4 inch groove or channel running around the inner perimeter of the frame to hold a sealant. Less screws, less places to leak. Thanks


If your hatch is one of the Bomar series 100's that used polycarbonate you can replace it with polycarbonate but it won't last as long as cast acrylic. Cape Dory, PSC and a number of other builders used this series Bomar.

There is only one hatch maker that I know of currently using polycarbonate/Lexan and that is Bomar in the same seris hatch you have. That series of hatch utilizes cast aluminum cross braces to support the Lexan. Lewmar, Goiot, Hood, Nibo, Gebo, Adkins & Hoyle, Man Ship etc. etc. all use cast acrylic and always have. Even the Bomar hatches used on Morris Yachts use cast acrylic. My Goiot cast acrylic hatch glass lasted 30 years!!!

As Dog mentioned Lexan foreshortens/flexes when stepped on and a guest can wind up in the galley if not careful. This is why Bomar installs cross bars to support the more flexible polycarbonate on the 100 series hatches. At a minimum you will kill the hatch to lens seal by stepping on a polycarbonate hatch, that was originally designed for cast acrylic, if it did not have support bars.


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## sailingdog (Mar 19, 2006)

Maine Sail said:


> If your hatch is one of the Bomar series 100's that used polycarbonate you can replace it with polycarbonate but it won't last as long as cast acrylic. Cape Dory, PSC and a number of other builders used this series Bomar.
> 
> There is only one hatch maker that I know of currently using polycarbonate/Lexan and that is Bomar in the same seris hatch you have. That series of hatch utilizes cast aluminum cross braces to support the Lexan. Lewmar, Goiot, Hood, Nibo, Gebo, Adkins & Hoyle, Man Ship etc. etc. all use cast acrylic and always have. Even the Bomar hatches used on Morris Yachts use cast acrylic. My Goiot cast acrylic hatch glass lasted 30 years!!!
> 
> As Dog mentioned Lexan foreshortens/flexes when stepped on and a guest can wind up in the galley if not careful. This is why Bomar installs cross bars to support the more flexible polycarbonate on the 100 series hatches. *At a minimum you will kill the hatch to lens seal by stepping on a polycarbonate hatch, that was originally designed for cast acrylic, if it did not have support bars.*


Worst case, you end up stepping through the hatch as the polycarbonate distorts enough to pop through the hatch...


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## poopdeckpappy (Jul 25, 2006)

Go lexan and look for MR-10, best in strength, best in scratch resistants and greater UV protection



> Lexan* MR10 sheets improved Margard® II coating resists abrasion and defies graffiti to ensure a "like-new" appearance for many years to come. The next generation of UV absorbers, Margard® coating now incorporates enhanced UV absorbers to protect the sheet from the debilitating effects of sunlight. As a result, Lexan* MR10 is accompanied by extended warranties that are your assurance of long term product performance; 10 yr. prorated replacement warranty against breakage, yellowing, abrasion, loss of light transmission and coating delamination.^ 15 year warranty against yellowing and light transmission for qualified dual glazed systems.** Virtually unbreakable.


PS; it's not as cheap as acrylic


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## hellosailor (Apr 11, 2006)

weephee-
Regardless of the choice (acrylic or polycarbonate) you should be aware that there are MANY grades of each. The stuff you find in the corner plastic store is "ornamental" grade designed for napkin holders and the the like.
The more expensive grades offer increasing scratch resistance (dried salt crystals are an excellent abrasive), increasing UV resistance, increasing chemical resistance (any petrochemical including most common cleaners will attack plastics) and increased strength.
If what you've got is good enough to keep you happy, by all means use it. Bear in mind that if you glue it into place and it is "ornamental" grade...in three or four years you may have a hard job chewing it out to replace it.
A lot of your options depend on whether you have a local supplier, versus a mail-order one, and what you can get from them since they are all sold in 4'x 8' sheets so if what you want isn't in stock, it can be hard to buy less than a whole sheet.


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## weephee (Oct 25, 2008)

Ok, so if I understand this properly my hatch came with Lexan and because it is not as structurally strong as acrylic, they needed and used support bars in the lid to carry the weight of people standing on the hatch. I should go with acyrlic because it is stronger and more uv protected and I should get a good quality acrylic which would not likely be obtained from a local supplier. I only want to do this once so I need the proper material. Can anyone recommend a supplier. Thanks


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## sailingdog (Mar 19, 2006)

No. The reason for the bars has to do with Polycarbonate's tendency to foreshorten or flex under a heavy impact. If the hatch is large enough, and the polycarbonate is hit hard enough, it could flex enough to either break the seal-which is very likely-or pop through the hatch-which is less likely. Polycarbonate is stronger than acrylic in the same thickness...

As for vendors, contact Select Plastics in CT.



weephee said:


> Ok, so if I understand this properly my hatch came with Lexan and because it is not as structurally strong as acrylic, they needed and used support bars in the lid to carry the weight of people standing on the hatch. I should go with acyrlic because it is stronger and more uv protected and I should get a good quality acrylic which would not likely be obtained from a local supplier. I only want to do this once so I need the proper material. Can anyone recommend a supplier. Thanks


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## Maine Sail (Jan 6, 2003)

weephee said:


> Ok, so if I understand this properly my hatch came with Lexan and because it is not as structurally strong as acrylic, they needed and used support bars in the lid to carry the weight of people standing on the hatch. I should go with acyrlic because it is stronger and more uv protected and I should get a good quality acrylic which would not likely be obtained from a local supplier. I only want to do this once so I need the proper material. Can anyone recommend a supplier. Thanks


Yes you can use Lexan, Makrolon or any other polycarbonate but only because your hatch was originally designed for it. If you had a hatch with no support bars you would be very un-wise to use a polycarbonate as it can be flat out out dangerous to do so.

Polycarbonate is a lot more shatter resistant to point impacts than acrylic but also far more flexible than cast acrylic. This flexibly is where the problem lies. Green water does not pose a point load impact but rather a broad load. Polycarb/Lexan, when doused with green water, can flex and break the seal/bond of the hatch to the frame where cast acrylic is far less likely to do so because it is stiffer.

Strenght is measured in many ways, polycarb is shatter resistant but flexible, cast acrylic is more shatter prone but stiffer. It is for this reason that upwards of 95+% of hatch makers use cast acrylic and not Lexan. Hatches are less likely to encounter a bullet than green water.

Despite the claims of MR10 and Makrolon it does not last nearly as long and is still not anywhere near as scratch resistant as a product like Acrylite GP cast acrylic.

You should really read Tony Dandrea's blog at Select Plastics. He is the industry guru and the Nigel Calder of marine plastics..

In your situation you could use either product and either wil suffice because you have support bars. Cast acrylic will last longer.

Select Plastics can also install a new lens for you and do it right..


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