# lexan thickness



## deniseO30 (Nov 27, 2006)

I found a supplier that has smoked lexan 3/16" thick. The original fixed ports for my boat were replaced with overlayed plexi by the PO. it's not a blue water boat. Is 3/16" thick enough? I think it is. but wanted some input before i buy the stuff. thanks!


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## resdog (Mar 29, 2006)

3/16" is a bit on the thin side. It'll will likely have a good bit of distortion if it's not in a frame. I wouldn't go below 1/4". I just replaced my 5/16" (8mm) acrylic with 1/4" and it was ok because it's bolted in place. I didn't want to pop for an entire 4x8 sheet of the 5/16" so I used the 1/4" which was more readily available.


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## deniseO30 (Nov 27, 2006)

Thanks resdog! Well, they do lay quite flat, I was thinking 1/4" also but the tell me lexan is pretty strong stuff. mine is screwed through oversized holes with washers for expansion and theres a SS lip on the top edge that makes water shed over the top. May I ask where you got your lexan?


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## Valiente (Jun 16, 2006)

I have 1/2" fixed Lexan portlights on the pilothouse and coach house that would likely stop small arms fire, but that's supposed to be "blue water grade". I replaced 1/4" Plexiglas fixed ports on my sloop with the same 1/4" and I would hesitate to go thinner than than, even with Lexan. I would get 1/4" as others are advising.

Opening ports: tempered glass.


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## hellosailor (Apr 11, 2006)

Denise, there's all kinds of Lexan (brand of polycarbonate) and similar materials. The supplier can tell you exactly which grade that is, and then the maker will have specs on their web site. Any polycarbonate will be better than most of what was used on "stock" boats, whether you want to go beyond what they have is another question entirely. There are some grades of polycarbonate that are specially scratch-resistant, UV-resistant, or both. Usually--that would mean ordering in whole 4'x8' sheets though, and they can get pricey.


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## sailingdog (Mar 19, 2006)

Denise—

The thickness really depends on how strong you need and how big the ports are. Also, you really want the anti-scratch and anti-UV coated Lexan. If this stuff isn't coated, then it won't last as long.

Check with an industrial sign supply company in your area, as they may have partial sheets available at a reasonable price.


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## Valiente (Jun 16, 2006)

This is true. Offcuts and wonky bits are common, or if you can deal with a slight flaw (say a small scratch close to the edge), you could save a bundle.


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## cutterorient (Feb 22, 2009)

*polycarbonate*

I replaced polycarbonate lenses on the three hatches on my boat and all the dorade boxes as well. 1/2 inch bronze tint was on there and thats what I used to replace it. Could I have gone thinner? Maybe. But everytime I am out in something that is really rough I never think about the hundred bucks I didn't spend. Are those lenses strong enough? It never enters my mind.


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## Trimmer (Sep 26, 2006)

I couldn't buck up for _Lexan_ , so I used 3/8 Plexiglass. It's been a few seasons now and It's in great shape! I found some great gasket material at (Mcmaster-Carr) on the net.


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## resdog (Mar 29, 2006)

deniseO30 said:


> Thanks resdog! Well, they do lay quite flat, I was thinking 1/4" also but the tell me lexan is pretty strong stuff. mine is screwed through oversized holes with washers for expansion and theres a SS lip on the top edge that makes water shed over the top. May I ask where you got your lexan?


I used tinted acrylic. For my use there was no reason to go with Lexan (polycarbonate). We use a supplier called Cope Plastics. They have offices all over the US.


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## GreatWhite (Jan 30, 2007)

Trimmer- which Gasket sealant did you select from Mcmaster-Carr?


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## Trimmer (Sep 26, 2006)

G.W. I used neoprene rubber. I think it was 3/16 thick. I bought about 2' x 4' and made my own gasket, no sealant of any kind. I drilled holes through the plexi just a little larger then the screws and used a washer w/ a built in rubber gasket (from ace hdwr).No leaks! Btw Mcmaster Carr has so much stuff I recall I had to call for guidence.


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## sailingdog (Mar 19, 2006)

One thing to remember. If you have to drill holes in plexiglass or polycarbonate, you really want to counter sink the holes on both sides so they don't become a starting point for a stress crack.


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## deniseO30 (Nov 27, 2006)

I think the rubber gasket makes more sense then various types of caulk, mostly because the white shows through the plexi or lexan when it's overlayed like it is on mine. Painting it black was a thought also. Darn shame the original fixed port frames are gone. (one has to wonder what PO's were ever thinking)


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## AllThumbs (Jul 12, 2008)

deniseO30 said:


> I think the rubber gasket makes more sense then various types of caulk, mostly because the white shows through the plexi or lexan when it's overlayed like it is on mine. Painting it black was a thought also. Darn shame the original fixed port frames are gone. (one has to wonder what PO's were ever thinking)


What are you talking about? The boats look way better once those frames are gone...


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## hellosailor (Apr 11, 2006)

The gasket approach is also more in line with what the various maufacturer's suggest on their installation data sheets. More time and effort than just gluing things together, so less likely to be found on a stock boat.


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## Gary M (May 9, 2006)

I have not tried it but I would think that the butyl rubber gasket strips would work well. It stays soft and therefore gives as needed and still seals.

Gary


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## GreatWhite (Jan 30, 2007)

The gasket strips sound like a good idea. I am just about to replace 3 large ports with Lexan (AR abrasion resistant) and they have a 2.5 inch thick SS frame inside and out so the gasket will be covered. I had planned on using a goopy sealant, but after reading this thread I am considering other ideas!


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## RXBOT (Sep 7, 2007)

*Denise*

If the existiing lexan is in good shape and you want to change to smoked 4 esthetic reasons, why not just overlay the new onto the old. That way even one eighth would be thick enough.


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## Trimmer (Sep 26, 2006)

When I did mine I used sheet neoprene. That way I had a seemless gasket. I installed the full sheet, and then _carefully_ trimmed the perimeter with a razor knife. Inside too. The usual trick is to use the external frames inside the cabin on the oposite port. Mine were plastic and broke apart removing them. I made some teak frames for inside the cabin. I'm a little impatient and drilled holes straight through the plexi .Oops no double countersink. As yet, no stress cracks either.( but I do have some stress) 
This project took a looong time. Buy beer!


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## bselly (Feb 11, 2009)

I just replaced my two hatches with 1/2" Lexan. I sprang for the top of the line UV resistant scratch proof stuff, which is absolutely bulletproof. A friend owns a sign shop, and even with friend pricing I still paid $600 for the 4x8 sheet! Supposedly, I can get 10-20 years out of this lexan without crazing. I can now make a transparent single piece slat that is stronger than my wooden slats. It will be great for watching bad weather while staying dry.


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## TSOJOURNER (Dec 16, 1999)

*Through Bolt or Self Tappers*

Re: Surface mounted fixed portlights.

I would imagine through bolts would be the strongest.

Do people have an opinion on whether using a black caulking compound equiv of 5200 and self tapers every 8 inches would be sufficient?


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## sailingdog (Mar 19, 2006)

Don't use 5200 on a boat. It really has little use on a boat. It is far too strong and permanent an adhesive for anything that may need replacing.

Self tappers are a bad idea in fiberglass. Fiberglass is rather brittle and doesn't take screws well. You're really much better off through-bolting.


matt2 said:


> Re: Surface mounted fixed portlights.
> 
> I would imagine through bolts would be the strongest.
> 
> Do people have an opinion on whether using a black caulking compound equiv of 5200 and self tapers every 8 inches would be sufficient?


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## cutterorient (Feb 22, 2009)

I agree; 5200 has no real use. Also, do not use Thiokol or its equivalents with lexan - use silcone which also happens to be easier to work with. Self tappers? No way. Pre drill holes in the lexan and then srew them into whatever is under it. You could throuh bolt too if appropriate/possible.


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## bselly (Feb 11, 2009)

I would never use 5200 to seal hatch, I always use 3M marine silicone. However, 5200 is AMAZING for patching torn sails. I have a mainsail that has torn completely across over a year ago. I glued a patch over the entire rip with 5200 and it still holds perfectly. I had it out in 30-40 mph winds this weekend with the full sail up, and had no problems. If you plan well, you can even make it look nice(I don't). I always keep old sail scraps and 5200 for emergency repairs.


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## TSOJOURNER (Dec 16, 1999)

*I agree*



sailingdog said:


> Don't use 5200 on a boat. It really has little use on a boat. It is far too strong and permanent an adhesive for anything that may need replacing.
> 
> Self tappers are a bad idea in fiberglass. Fiberglass is rather brittle and doesn't take screws well. You're really much better off through-bolting.


I agree, I have never been happy with it, though I think it is probably strong enough. I may redo one window and see how it goes.

This is one of the things I got a "professional" to do when I first got the boat.


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## sailingdog (Mar 19, 2006)

BTW, when you drill holes in the Lexan or Plexiglass, don't forget to countersink the holes ON BOTH SIDES so they don't become a starting point for nasty stress crack.


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## AllThumbs (Jul 12, 2008)

Go ahead with the 3/16 lexan. Lexan is very, very tough. Once it's on, I doubt you could break it with a hammer. If it's plexi, on the other hand, you need to go thicker.

I have folded lexan in half in the vice without breaking it.


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## TSOJOURNER (Dec 16, 1999)

*Lexan is predrilled*



cutterorient said:


> I agree; 5200 has no real use. Also, do not use Thiokol or its equivalents with lexan - use silcone which also happens to be easier to work with. Self tappers? No way. Pre drill holes in the lexan and then screw them into whatever is under it. You could throuh bolt too if appropriate/possible.


Yes the lexan is predrilled, but I believe self tappers were used into the fibreglass.

I think I will try replacing one of the windows and in the process it will become clear whether it has sufficient adhesion and whether the other windows need replacing.

The lexan overlaps the outside of the windows by about 4 inches all around, so quite a bit of surface area attachment.

I read somewhere that if the lexan overlaps the fiberglass and you don't want to see all the goop behind the lexan then you should paint the back of the lexan where it overlaps. But I am not sure what paint to use?


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## hellosailor (Apr 11, 2006)

Matt, call GE's toll free number. Ask the lexan ("structured plastics") division and the silicone sealants division if you can use silicone seal to glue Lexan to fiberglass.

I'm fairly certain they will all tell you NO WAY. Silicone products simply do not bond to Lexan, you not specific adhesives and often primers for them, or the Lexan will rather quickly unbond from the adhesive.

A couple of free phone calls will save you from a major redo.


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## Maine Sail (Jan 6, 2003)

deniseO30 said:


> I found a supplier that has smoked lexan 3/16" thick. The original fixed ports for my boat were replaced with overlayed plexi by the PO. it's not a blue water boat. Is 3/16" thick enough? I think it is. but wanted some input before i buy the stuff. thanks!


Denise,

You really should be using Cast Acrylic.

Not my words these are the words of Select Plastics..


"Acrylic -vs- Polycarbonate       
 
 Written by Tony D'Andrea  Monday, 09 February 2009 22:01  Consider the Following:

All major hatch, portlight and window manufacturers use Acrylic in offshore / bluewater marine products.
Acrylic is more scratch resistant than standard (9034) polycarbonate.
Acrylic is significantly more durable when exposed to Ultra Violet radiation (sunlight).
Acrylic is less expensive than Polycarbonate.
Don't misunderstand my preference for acrylic. I buy, use and sell a significant amount of both products and each has its application. In my humble opinion Acrylic is more durable, versatile and cost effective in the hands of a skilled craftsman than polycarbonate.

Additional considerations may include polycarbonate with UV and scratch resistant coatings. While these products are heavily promoted by several manufacturers and carry 5, 10 even 15 year warranties the following information has been reported in "real life"applications:
Polycarbonate is impact resistant. When its new it is almost impossible to break.
Small quantities (less than a 4 by 8) in gauges over 1/8th inch are difficult to to find in the uv/scratch resistant grades.
Colors are limited. Only two standards (gray and bronze). Try and find anything thicker than 1/4 in UV/ scratch resistant!
Polycarbonate foreshortens when subject to static or dynamic loads. What this means is if you replace your hatch lens with polycarb, seal it and then step on it the ductile material will deflect (bow) in the center. One of two things may happen. 1st you will surely break the watertight seal, 2nd you may end up with a leg in your galley.
As for the warranty: The original owner is warranted against failure subject to the material being submitted to the distributor for evaluation with the original invoice subject to actual replacement cost at the time of purchase. I guess this means they sell you a new square of material and apply the old payment to the new cost. How about the labor to fabricate the part, install it and sealant? Why take the chance?
Polycarbonate is a great material, The US Air force uses it for fighter canopies! I sell Polycarb to the USCG and US Navy. Remember they don't mind using it because we are paying to replace it every three years.
Both Acrylic and Polycarbonate have specific uses and installation requirements.

Cast Acrylic (of a specific thickness) is in accordance with CE and ABYC guidelines, and installed on virtually all of the big blue water sail boats produced on both sides of the pond. Polycarbonate is commonly used as a replacement due to its ease of fabrication and incredible initial strength. The USCG and USN require Polycarbonate on their vessels but they also have a PM cycle of 36 to 42 months for change out. My Tax dollars at work...

Due to its ductility Polycarbonate it is more challenging to install. I have seen Sika Flex 295UV with primer and Dow 795 both mentioned. I use and recommend both. Dont go over 4 ft continuous length with a fixed portlight. Remember the coefficiant of thermal expansion for Acrylic and Polycarbonate is in the neiborhood of .000039 per inch per degree F. That means an 8ft plastic port will expand and contract up to 1/2 of an inch from the coldest day in Feb to the hottest day in summer. WOW!! Compartmentalize the job. It will be easier to install and less prone to leaks.

Never ever bolt a plastic portlight in place. Screws are fine to hold a lens till the adhesive cures. Take them out asap and fill the holes with the afformentioned products. Both of these products are rated at 700 + percent elongation before tear. Strong flexible and UV resistant. Kinda like me!

Been to a boat show lately? Seen any screws? Glass is good so long as your boat does not twist or torque. Show me a fiberglass boat that does not twist and I will show you a cocktail barge tied to the dock."


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## hellosailor (Apr 11, 2006)

"The USCG and USN require Polycarbonate on their vessels but they also have a PM cycle of 36 to 42 months for change out."
So, do you think that's all pork barrel spending? Or, that poly _really is superior _provided you have the budget to maintain it?

Whether it is acrylic or poly, genreally if you want anything beyond the most common grade of clear stock, it seems you have to order in full 4x8 sheets. Only the largest of suppliers (who generally won't be local) carry anything that has special qualities, But something like GE MR10 poly (scratch and Uz resistant) will be commonly available to them, as it is a standard for architectural and other uses--like train windows, which are required by federal law to be bullet-resistant. (Go figure, the train itself doesn't have to be, but the windows do.)


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## Maine Sail (Jan 6, 2003)

hellosailor said:


> "The USCG and USN require Polycarbonate on their vessels but they also have a PM cycle of 36 to 42 months for change out."
> So, do you think that's all pork barrel spending? Or, that poly _really is superior _provided you have the budget to maintain it?
> 
> Whether it is acrylic or poly, genreally if you want anything beyond the most common grade of clear stock, it seems you have to order in full 4x8 sheets. Only the largest of suppliers (who generally won't be local) carry anything that has special qualities, But something like GE MR10 poly (scratch and Uz resistant) will be commonly available to them, as it is a standard for architectural and other uses--like train windows, which are required by federal law to be bullet-resistant. (Go figure, the train itself doesn't have to be, but the windows do.)


I know polycarb is more shatter resistant and is probably the reason the military uses it. And yes I think it's probably pork barrel too..

I'm fortunate enough to have a good plastics company up here in Maine. I just replaced the glass in two Goiot hatches for under $300.00 using Acrylite GP. This included the CNC cutting and everything and they had it in stock and I did not need to buy a whole sheet.

Select plastics is a great source and they have rebuilt hatches for me before. The last time I spoke with them they could not get Lexan in 3/8" or 1/2" smoke with scratch resistance and UV. They also convinced me to not use it due to the potential for bonding failures due to the flex characteristics. They basically said if you can't get UV polycarb not to bother as it will be a waste of money on a boat..

In terms of plastic hatches & port windows Select Plastics is probably one of the most knowledgeable companies in the industry and are the largest in the world who do hatch repair..


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## scottyt (Jul 19, 2008)

not stirring the pot here

personally i would go with poly. i have seen acrylic basicly explode under pressure, it will flex to a point then bust with force enough to stick a shard thru drywall. if you want strength with scratch resistance use tempered glass, over a certain size it will be cheaper to use glass.

if you are doing pilot house windows, size em to use school bus rear windows, i bet with some searching at scrap yards they would be very cheap

i will be doing some companion way boards soon with poly inserts like a raised panel door. for privacy i plan on getting some of the self adhesive child sun blockers like this stuff here  but my windows will be about 12 by 18 so it wont need much thickness


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## Maine Sail (Jan 6, 2003)

scottyt said:


> not stirring the pot here
> 
> personally i would go with poly. i have seen acrylic basicly explode under pressure, it will flex to a point then bust with force enough to stick a shard thru drywall.


Scotty,

This is an O'day for coastal sailing and they are small windows. Considering just about every sailboat builder out there and every hatch manufacturer uses Acrylic, and has been for a long time, and you can't get Lexan in many thicknesses, with UV and scratch resistance, why would you suggest Denise reinvent the wheel so to speak?

I sailed in the Perfect Storm aboard a Shannon using acrylic hatches, as most all do. We took a serious pounding and never even came close to imploding those hatches.

A friend of mine here in Portland own a fleet of commercial long line boats (Deadliest Catch type steel fishing boats) and they too use Acrylic on board. Builders like Hinckley, Swan, Morris, Malo, Halberg Rassy, Shannon, Passport, Hylas & Valliant and hatch makers like Bomar, Lewmar, Goiot, Adkins & Hoyle, Hood, Nibo and others all use acrylic. I can't remember the last time I heard of a hatch or acrylic portlight imploding. Perhaps it's happened but I'd venture to guess Denise will not be out in 40 foot seas.

I think on any small coastal cruising boat the biggest priority is keeping a seal and preventing UV damage. As Tony D'andria states (owner of select plastics) Lexan flexes too much under foot and you can risk breaking the seal by simply stepping on a hatch. There is a big difference between impact resistance and flex. Flexing under foot or wave can break seals on polycarb hatches.

The hatch glass that just came out of our boat is 30 year old & acrylic. I could still walk on it but barely see out of it. The boat has tens of thousands of miles on her and 5+ years of circumnavigation/cruising. I stayed with acrylic because it works, is strong, and lasts a long, long time, 30 years long.

If Denise needs to replace port lights ever 30-40 months I don't think that is a wise investment.

Make your own decisions but before you do please pck up teh phone and call Select. I too wanted Lexan before I learned the pros & cons..


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## scottyt (Jul 19, 2008)

yes for smaller boats windows i dont think it will make much difference. personally i would not go over about 12 by 12 with acrylic unless 3/8 or thicker. i want the poly for the boards for security reasons, and remember it will not be for holding back a wave. i plan on using 3/16 because i can get it locally for pretty cheap and in my case i want the flex

i have seen the results from a companion board made from 1/4 inch acrylic kicked in, i did it on a boat that got donated to the charity that i bought my boat that i was looking at. it did not take much and there where pieces found in the v berth. ( breaking it was with permission )


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## hellosailor (Apr 11, 2006)

"they had it in stock and I did not need to buy a whole sheet. " What riles me is that almost all plastics shops will indeed charge you for the whole sheet--even if they don't sell or deliver it to you. I know, it has to sit in inventory until someone asks asks for the stuff...but if I'd paid for the sheet, I want the sheet.

Even on a coastal boat, there are reasons to consider structural glazing instead of what the builders use. They have to skimp on costs or else they're out of the market. But, even coastal, what happens if a storm hits and your whisker pole breaks free and shoots through your portlight? 

I'd rather follow the conclusions after the Fastnet disaster, i.e. that the entire cabin top, doghoise, whatever, be fully as strong as the hull itself.

Or at least, as strong as the screen doors on a submarine.(G)


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