Best long-term window material choice?

[AiniA]

I have had very good success using 3M VHB tape to install windows on the boat. You can get various widths and thicknesses. It would handle expansion of the plastic quite well. I am a fan of cast acrylic over polycarbonate, not because the polycarbonate cracked, just that it is so easily scratched.

[Sailing4Jesus]

SUGGESTION:
If ya want to avoid the hassle of stowing Marine Plywood Storm Shutters aboard, BULLET PROOF GLASS ought to be a viable alternative. U.S. Military Disposal Yards are a good place to search if you do not have the funds sufficient to purchase NEW. I have known of several Ocean Sailing Yachts that have Bullet Proof Glass and all those owners stated that the convenience of not having to store Marine Plywood Storm Shutters aboard far outweighs the cost of Bullet Proof Glass Windows.

Senior Chief, U.S. Navy, Retired

[JPA Cate]

Second the notion of using shadecloth covers for the "windows". If you use black, you can see easily through it, but white reflects more UV.

Ann

[Minggat]

Originally Posted by SunnySky

Minggat:


What made you choose to go with Makralon vs a cast acrylic? Also even with the impact of UV somewhere with the sun is as intense as Hawai'idoes having a less than 6 years lifespan of new AR2 polycarbonate window seem within a normal range?


.

The thickness of the material.
Cast acrylic comes in thick rigid plates. Great for hatches and probably your windows.
Makralon, while semi rigid, comes in thin sheets that can be sewn.
That semi-rigidity makes it great for dodgers. No wrinkles, and can bend to follow the curves you need. It also has the clarity of plate material. New Strataglass next to new Makralon, you can see a graininess in the Strataglass.

I built my dodger hardtop with bolt rope tracks top and bottom. So they slide into place, then zipper together.

Each window has it's own "pillowcase" for storage to protect from scratches and keeps dust off of them while stored up against the headliner.

[Michael Pope]

Hey Glass is heavy! If you go the tempered glass route you need good flat one plane mounting sealing surface . You need to make accurate templates for each window and take them to the big wholesale glass suppliers and have them fly the templates to the Glass plant and wait for them to deliver . You can hit
6 mm tempered glass with a hammer and only hurt your hand and they will be clear and beautiful 30 years later. You can always stick on coloured coatings , Tint screens etc and replace them when UV gets them . Cars use glass for a reason !! If you cannot see through them ten years later why have windows?

I do not like the weight either BUT! -- Also if you are building boats the frames have to be more twist resistant and more rigid so if you want good window you have to build a better boat------ I like that idea -- Mike Pope

[j.g.evans]

See my advice on replacing Cal 29 ports. My method allows for thermal expansion. Early C&C boats with glued ports were famous for cracked acrylic ports.

[slug]

Originally Posted by AiniA

I have had very good success using 3M VHB tape to install windows on the boat. You can get various widths and thicknesses. It would handle expansion of the plastic quite well. I am a fan of cast acrylic over polycarbonate, not because the polycarbonate cracked, just that it is so easily scratched.

In order to achieve VHB ‘s bonding properties you must apply clamping pressure

This is very difficult to achieve with boat windows

Tape is a bad choice

[SunnySky]

Thank you all very much, everyone's input has been really helpful in my thought process.



wrwakefield, Sailing4Jesus, and Michael Pope
I appreciate your advice on glass options, with double pane tempered glass which is strong enough to avoid needing storm boards being the glass option I would go with if weight wasn't such a big factor for me. It's just really difficult to choose to add so much additional weight given the thicknesses required to trust it being strong enough...


JPA Cate and slug,
Even though I think my installation was appropriate I'm going to both reinforce around the window opening to stiffen it up and go with a slightly thicker layer of Sikaflex 295 UV


Hbrew,
I really like those shades that snap over your windows.


Hbrew and JPA Cate: Is there a particular brand or type that you would recommend? Would making them out of standard agricultural shade cloth be ok or would I need to worry about scratches caused by a small amount of movement combined with some salt crystals from after saltwater/spray dries? Have you had any issues with the material shrinking in the sun and then not being able to reach the original snaps?


Minggat,
That makes sense for your purposes and helps boost my confidence that shifting to cast acrylic (plus shade most of the time) would be the best path forward.


Slug and Aina:
Judging by my (older) Vetus cast acrylic hatches which use cast acrylic still being in good shape I'm definitely leaning towards cast acrylic over polycarbonate.


If the 3M VHB tapes as good or equal to Sika Flex 295 UV I'm all about that as an option (especially since it's non-hazmat, which makes my life a lot simpler to get it both now and in the future... Not to mention the very short shelf life of Sika primers being something I would like to avoid IF and only if possible without compromising strength and reliability..)


Regarding VHB tape and clamping pressure, my last time I installed my windows with sika 295 UV I didn't want to drill any holes in the polycarbonate when I mounted my old windows I used boards to push down on the windows by screwing the boards into the area surrounding the windows to clamp the windows down (and then I removed and filled the holes with thickened epoxy..). Do you think that would be a good approach with VHB tape, or am I better to stick with Sikaflex 295 UV?


J G Evans
Thank you about the advice on using black raw rubber from a tire place if available, link didn't work for me though, for other people viewing this it is at: https://www.cruisersforum.com/forums...-a-231198.html).

[wrwakefield]

Originally Posted by SunnySky

...
Regarding VHB tape and clamping pressure...

Just a comment on my limited experience with VHB tape: In 2014 we attached some moulded clear lexan covers over some opening ports using only VHB tape [per instructions from cover manufacturer.] No mechanical fastners.

Here is a brief blog post on that project, with photos.

I only used hand pressure [leaning on it while standing on the dock...] and they are still bonded tight without any indication of coming loose, and no water leaks either. [I can see the outboard side of the tape through the clear covers...] They have seen 70+ knot winds, and endure several freeze-thaw cycles every winter. [Down to zero °F to date.]

I would absolutely consider using VHB to affix plastic windows in place- buying thick enough VHB tape to accommodate any slight gap(s) between the two planes being bonded, as well as different thermal expansion coefficients.

An additional consideration I would explore if using VHB tape on a critical topside weathertight seal [I don't consider our rain covers critical...] is hding the tape bond against the clear window from UV exposure. [e.g., paint, wood or metal frame, etc.]

In case this is of interest.

Best wishes with your project.

Cheers! Bill

[HBrew]

Hbrew and JPA Cate: Is there a particular brand or type that you would recommend? Would making them out of standard agricultural shade cloth be ok or would I need to worry about scratches caused by a small amount of movement combined with some salt crystals from after saltwater/spray dries? Have you had any issues with the material shrinking in the sun and then not being able to reach the original snaps?

Here is the maker of my shades - chosen by the manufacturer of my boat - https://www.sergeferrari.com/product...e/batyline-iso

I guess they use it for making outdoor furniture. I have had them on the boat continuously in tropical conditions for five years now and they are still fine, they are a tight fit, but I think that is intentional.

Hope this helps.

[slug]

Originally Posted by wrwakefield

Just a comment on my limited experience with VHB tape: In 2014 we attached some moulded clear lexan covers over some opening ports using only VHB tape [per instructions from cover manufacturer.] No mechanical fastners.

Here is a brief blog post on that project, with photos.

I only used hand pressure [leaning on it while standing on the dock...] and they are still bonded tight without any indication of coming loose, and no water leaks either. [I can see the outboard side of the tape through the clear covers...] They have seen 70+ knot winds, and endure several freeze-thaw cycles every winter. [Down to zero °F to date.]

I would absolutely consider using VHB to affix plastic windows in place- buying thick enough VHB tape to accommodate any slight gap(s) between the two planes being bonded, as well as different thermal expansion coefficients.

An additional consideration I would explore if using VHB tape on a critical topside weathertight seal [I don't consider our rain covers critical...] is hding the tape bond against the clear window from UV exposure. [e.g., paint, wood or metal frame, etc.]

In case this is of interest.

Best wishes with your project.

Cheers! Bill

The technical document for the 3m tape states 15 psi clamping pressure

Difficult to achieve this outside of pro workshop

“Bond strength is dependent upon the amount of adhesive-to- surface contact developed. Firm application pressure develops better adhesive contact and helps improve bond strength. (Steps C and D) Generally, this means that the tape should experience at least 15 psi (100 kPa) in roll down or platen pressure. (Sources- page #4)”

[SunnySky]

Thank you very much wrwakefield, Hbrew, and slug :-)
Protecting the sikaflex or tape from UV exposure is definitely a critical detail I will pay close attention to this time around.
I can't help but notice ~15 psi also conveniently happens to be atmospheric pressure. It seems like going the 3M tape route I could get close to what the pros do by using the vacuum bagging system that I already use for doing epoxy vacuum bagging/VARTM resin infusions. Since my Robinair 15600 two stage rotary vane pump can easily draw vacuum down to below 150 microns, I would have just shy of 14.7 psi of clamping pressure over the entire surface if I bagged both sides of it. Sound reasonable?

[Michael Pope]

my quick advise is to take it easy on the vacuum as you willbe exerting the vacuum pressure over a far larger area than the actual Seal area and it is quite easy to over pressure the seal area and end up with an inadequate thickness of seal and lack flexibility or even break the window or whatever . One Half an Atmosphere is generally too much pressure and you can get that with a "Shop Vac" Do a dry run and check deflections . Saw a guy break our 10ft X 40ft 3/4" Glass Table trying to glue a little door together . I think heenjoyed his unemployment though! Good Luck Mike Pope

[redneckrob]

Originally Posted by Sailing4Jesus

SUGGESTION:
If ya want to avoid the hassle of stowing Marine Plywood Storm Shutters aboard, BULLET PROOF GLASS ought to be a viable alternative. U.S. Military Disposal Yards are a good place to search if you do not have the funds sufficient to purchase NEW. I have known of several Ocean Sailing Yachts that have Bullet Proof Glass and all those owners stated that the convenience of not having to store Marine Plywood Storm Shutters aboard far outweighs the cost of Bullet Proof Glass Windows.

Senior Chief, U.S. Navy, Retired

It's a catamaran, they're very weight sensitive. Bulletproof glass is insanely heavy and crazy thick, as well as being very unwieldy. It also goes yellow in 10 years, if you got surplus you'd already be an unknown part of the way into that 10 years.

I'm retired military as well, you gotta take much of what you learned in the military and flush it down the toilet when it comes to cruising. There are things we learned like celestial nav and rules of the road that are universal, but much of the rest is actually worse than knowing nothing. At least if you knew nothing you'd actively seek to learn more, where as we're dangerously self-confident about things that we think we know but are actually much different in this world than our previous life.

[CaptainMarkS]

Originally Posted by SunnySky

I have four pilothouse windows which I replaced less than 6 years ago that already have one crack over 6" and two cracks about 2.5" long along with extensive crazing which to me seems like an overly short lifespan for 1/2" AR-2 polycarbonate. I realize the intense Hawaiian sun my hatches/windows have had to deal with can be pretty hard on polycarbonate and acrylic but given that I installed 10 new hatches which are still fine prior to replacing these four windows it seems like the coating (which was not damaged...) should have protected the underlying polycarbonate much better and I really want to choose a longer-term solution but after all my research the first time around I'm not aware of an option I can reasonably expect to be better than what I did before.


In terms of mounting details from less than 6 years ago:
The windows are not simple rectangles but for the purposes of giving an approximate size two about 24” x 37” and two about 24” x 34” with about 2 1/4" of their perimeter mounted with Sikaflex 295 UV after lightly sanding the surface to be bonded and using Sika Primer 2009 D and Sika Primer 215. All products used were not expired and from fresh containers. All corners are about 2" radius and there are no drill holes or mechanical fasteners to cause a stress concentration. I made sure to have an even film thickness. I was under the belief I was getting Marolon AR from Professional Plastics Inc aka proplas.com but currently on their website I noticed a disclaimer that "Makrolon® AR is our preferred brand, but some items sold on this page may vary."


I honestly am not 100% sure if what I last installed was Makrolon or not, or if the proplas website had the disclaimer of possibly substituting brands at the time of my two purchases (one prior to sailing north from Bellingham and one when I was anchored off of california and actually finally getting around to installing them..).


Either way I have a hard time with Professional Plastics response that "The life span of Polycarbonate is 5-7 years in direct sun / around water with more intense UV rays it maybe less. Your material also had a AR2 Coating which is a factory spray on coating, when you sanded the material you also sanded off the coating and once you added any kind of primer or modified the material that invalidated any warranty."


Given how good all 10 of my cast acrylic hatches still look it's tempting to go with cast acrylic for these windows this time around BUT I'ver heard from multiple people that sound like they know what they are talking about that the AR-2 polycarbonate is a better choice for this application and that it should last MUCH longer than it did?
Any thoughts?

Hey, @sunnysky, what did you end up choosing? How has it held up? I now have a similar challenge.