Acrylic and/or Polycarbonate? Confused!

[Surf City]

Yes, I am but it seems that there really are two thoughts to the process. There are plus and minus to both but I am not wanting to replace them sooner than later in the future. Once will be just fine.

Acrylic seems to have worked well in the past on this boat. But I'm hoping cast Acrylic is a step above what was OEM original. I also like the use of window tint.

Is cell cast acrylic a uniform process with all manafactures in casting? Benjamin you mention Acrylite brand - are there other manafactures that have good products?

Thanks for all the great advice.

[Benjamaphone]

Yes, there are a few others. Gord recently posted a few in the construction/refit section under the thread Portlight Glass. It used to be that any plastic coming out of mexico was of inferior quality, however these days it is possible to find the good stuff. Make sure its made in the US just to be safe. A quick search for quality hatch manufacturers and hatch repair shops should be able to source some out for you.

[drew23]

ever-so-slightly off topic:

I've just replaced all of my 20-year-old plexiglass windows - they were glazed well past the point of being transparent, at best they provided light in the cabin. I replaced them all with 1/4" Lexan, which I had custom-cut locally and installed with Sikaflex 295 UV. I installed two of the windows using butyl tape and then Sika, but I'm not perfectly happy with the results - and since I couldn't find any more butyl tape locally, the point is moot.

My question: I know eventually these windows will get scratched and blurry again. I knew that from the outset, but couldn't afford acrylic. What can I do about it though? Is there some sort of fine buffing compound that, applied with a buffer pad attached to a drill or grinder, can buff out the scratches and make the windows perfectly clear again?

[Benjamaphone]

The best way to preserve your lens is to avoid using any soaps or detergents. Even mild cleaners will react and create micro scratches that will eventually lead to crazing and fogging. If you have to clean your lens, use an acrylic cleaner. The best ones can be found at art shops. This product is also pretty good; novuspolish

[sailvayu]

I have been wondering about the adhesives and sealant. I have used the Sikaflex 295 UV and was really disappointed with the results ended up redoing it after 1 year. Seems 100% silicone works best but wondered about using the butyl to set the material in and then seal with silicone. And then there are the paint on sealants over the caulk. Just wonder what others have had success or lack of success with.

Wayne Canning, AMS
projectboatzen

[Pblais]

I have been wondering about the adhesives and sealant.

Sealants need to deal with the expansion and contraction of dissimilar surfaces. It's why 5200 can be in many applications a poor choice - it won't expand and contract! So when picking a sealant you need to consider the materials that are both boned and need to expand and contract at different rates. 5200 is the worst choice for ports as they have the most dissimilar materials and the most subject to extreme differences in temperature.

So what were the two materials you were sealing? How much expansion / contraction room was there?

I have Atkins and Holye ports. The cast acrylic is as clear as new. The ports are coming up on 20 years. I rebedded some ports that were bedded by the PO in 5200 and now with silkaflex. The acrylic is still bedded in the original bedding in the Al Mag frames. The 5200 failed even if it took a long time.

[sailvayu]

I am talking about sealing the lens in the hatch frames or windows in the boat. I know 5200 is not the right stuff for this. I just want to see what others have used

Wayne Canning, AMS

[fabian1956]

A interesting article that may help is located at How to install boat windows and port lights.

[s/v Jedi]

I know this (first hand, unfortunately):

• Acrylics (Plexiglass) stay good much longer than poly-carbonates (Lexan).
• The cut edges must not be exposed to UV. When UV enters here, it will travel through the whole panel.
• You should use a mar-resistant and UV filter coating.

I recently read that Lexan is only stronger than Plexiglass for point-loading. It didn't check that yet, but think the source was credible. Dropped winch handles falling on it etc. would be the deciding factor for making the choice.

An un-coated panel with the new user-applied film that works on plastic windows seems like the best answer.

Restoring: outside surface problems can be dealt with, we just did that on our Lexan pilot house windows. You start with 120-grit wet sanding and work your way up to polishing compound (big job). We finished with a polymer coating that holds up to an acceptable level. But damage inside the panel, like deep UV grazing, can't be restored.

cheers,
Nick.

[Maine Sail]

Originally Posted by sailvayu

I am talking about sealing the lens in the hatch frames or windows in the boat. I know 5200 is not the right stuff for this. I just want to see what others have used

Wayne Canning, AMS

Wayne,

Dow 795 is what many builders and manufacturers use to bed. It is a structural glazing silicone and is widely available.

We have had one manufacturer join this thread, and one who BTW makes excellent ports and hatches, of very high quality, and the advice given is excellent.

Below are some quotes from Tony D'andrea who is the Acrylic & Polycarb guru in the marine industry. He is the Nigel Calder of portlights and hatches and owns the largest hatch warranty & repair facility in the world called Select Plastics. He also worked for Cyro the makers of Acrylite for a number of years and really knows his stuff.

As a racer I have seen just about every thing from a spin pole to a winch handle dropped on cast acrylic hatches, most hatches with the exception of a couple of Bomar's (I think the 100 series with the support bars) are cast acrylic. Not once in my 30 years of racing sail boats have I seen an acrylic hatch crack or shatter. That's a LOT of shute launches and a lot of people on deck standing on hatches.

My lenses in my Goiot hatches were finally replaced last spring at the 30 year mark. One of them is 26" X 26" and had well over 30k nautical miles put on it by a good friend who owned it before me. She went from South America to Europe to Labrador to Alaska and back.

In 30 years this 26" X 26" cast acrylic never once leaked nor did it crack or show any signs of it. It was walked on by 300 pond individuals and had been whacked by numerous items over the years. While it was not all to clear at 30 years I could still actually see out of it..



Tony D'andrea on Acrylic vs. Polycarbonate:


"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.

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."

Tony on Sealants:

"I hear the question as to which sealant to use when bonding Acrylic, or Polycarbonate to aluminum, stainless or FRP over and over and over.....
Well here goes... The only three adhesives I would consider using are Sika Flex 295 UV with the primer, GE SG-4000, and Dow 795. Using the correct adhesive is only 1/2 the battle. Do not apply the sealants below 50 degrees F. The temperature must maintain at least 50F during the entire 21 day cure cycle. Cut this corner and your finished before you start. Preparation of the bond area is also very/ very important. DO NOT TOUCH THE BOND AREA WITH YOUR BARE HANDS! Contamination from the dirt and skin oils will make a solid cure impossible. You may clean the FRP and metal with acetone to prep the area but if you touch the Lexan or Plexi with harsh solvents you will ruin the portlight. A 50/50 mix of isopropal alcohol and distilled water will work well to clean the plastic if needed. Remember that clean enough is not clean enough."