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Go Back   SailNet Community > On Board > Gear & Maintenance > lexan thickness
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Topic Review (Newest First)
03-29-2009 01:32 PM
hellosailor "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)
03-29-2009 02:31 AM
scottyt 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 )
03-29-2009 01:51 AM
Maine Sail
Quote:
Originally Posted by scottyt View Post
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..
03-29-2009 01:24 AM
scottyt 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
03-29-2009 12:59 AM
Maine Sail
Quote:
Originally Posted by hellosailor View Post
"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..
03-29-2009 12:34 AM
hellosailor "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.)
03-28-2009 04:40 PM
Maine Sail
Quote:
Originally Posted by deniseO30 View Post
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."
03-27-2009 12:15 AM
hellosailor 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.
03-27-2009 12:09 AM
matt2
Lexan is predrilled

Quote:
Originally Posted by cutterorient View Post
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?
03-26-2009 11:39 PM
AllThumbs 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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