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  Topic Review (Newest First)
11-29-2014 11:58 AM
Re: Acrylic or Polycarbonate for windows

Acrylic expansion is approximately 9% greater than polycarbonate. And whatever figure you find on line, double it if you're looking at gray, bronze or another dark color. It's HARDER than poly so it's more scratch/abrasion resistant. Poly is softer so it will take a blow with a hammer or a flogging shackle but will scratch more readily. Both are/can be UV protected and will probably outlast your ownership of the boat.


This is the same joint I've used dozens of times at work. In the industry it's called a "four-sided flush glazed joint". I design this type of thing for a living, really. Similar to what others have said, shape the glazing, smooth the edges, make it look real nice. Be sure it overlaps the opening by about 1" on all sides. Apply structural glazing tape (3/16" minimum) to the opening so when the glazing is applied, the tape will be 1/4" from its edge. Be careful and make it round the corners, leaving the outside release tape on. Make it pretty. Now, fold down/up the corners of the tape so you can reach them and carfuly place the glazing. The little bit of exposed tape will grab quite well. Once you're satisfied with the arrangement, grab that tape and pull back at 45 degrees. It will unzip. Press HARD on the glazing, then use a soft cloth to protect the surface and beat around the tape with a rubber mallet. At this point, the tape should be 1/4" away from the edge of the glazing with no bubbles showing. Now mask around the edge of the portlight, on the boat and on the glazing. With a razor knife, trim a real nice perimeter 1/4" away from the edge of the glazing (on the boat). Also, trim the masking tape to the very edge of the glazing. Apply a bead of 795 around the edge, forcing it into the space created by the glazing tape. Use plenty. This is the most important part. TOOL the joint. Use a plastic spoon and a spray of water to make the joint look like a gasket. DO NOT SKIP THE TOOLING STEP. regardless of how good you think it looks. An untooled joint is a leaker. An unwarrantied leaker. Immediately remove the masking tape being careful not to get all that unused silicone all over everything. Your light should look like it's installed with a rubber gasket.

This is the same method they now install high-rise windows with. Please note there are no screws involved. They are not needed, add places for water to get in and stress to crack the glazing due to expansion cycles.

Have a great graphic to add but the site won't let me right now.
11-27-2014 10:38 PM
Re: Acrylic or Polycarbonate for windows

Acrylic does expand more that polycarbonate with temperature increases but doesn't scratch as easily nor craze as quickly. A good acrylic port installation is good for decades while polycarbonate needs to be replaced often to maintain optical clarity. That is the reason that almost all major hatch manufacturers use acrylic - the exception is Bomar on some models.
11-27-2014 05:36 PM
Re: Acrylic or Polycarbonate for windows

Which expands more in hot climates, acrylic or polycarboante??
12-06-2009 11:59 PM
Originally Posted by Faster View Post
Say that's a typo..... otherwise your boat's been on the hard for close to 20 years??? yoiks!
Sad, but true . We lived on her from '81 to '91, but since then she's been about 1200 miles away from me. I hope to either move down there and fix her up, or find someplace to store/work on her up here, but for the moment she's still sitting.
12-06-2009 11:14 PM
Originally Posted by Incarnate View Post
.....The boat has been up on the hard since '91, in the direct Florida sunshine, .....
Say that's a typo..... otherwise your boat's been on the hard for close to 20 years??? yoiks!
12-06-2009 11:05 PM
Lexan definitely does scratch easily, and that was the biggest downside to our use.
That why I mentioned the MR-10, it's superior to std lexan in both scartch & UV protection, I'm using it on our forward hatch and it's been there 2 yrs now
12-06-2009 10:19 PM
Use of Lexan

I just wanted to post a quick note about the use of Lexan. We replaced the large-area ports (windows?) on our Fantasia 35 back in the mid 80s, using half-inch Lexan. The material came from the bulletproof windows in a bank, but since it was surplus or reclaimed, I don't know any more details on the exact type. We used those windows, full-time liveaboard, for maybe another 5 years, and never saw a single stress crack or any crazing.

The boat has been up on the hard since '91, in the direct Florida sunshine, and I visited it last year. The windows are still solid, and I didn't see any evidence of cracking or crazing, and that's with 20+ years of weathered exposure. The Lexan has some patchy tan discoloration from the many stainless through-bolts rusting lightly, but I don't expect that would be hard to clean up.

Perhaps we were just lucky on the cracking thing, or perhaps it's the really heavy thickness we used. Lexan definitely does scratch easily, and that was the biggest downside to our use. After a few years they were good for letting light in, but not for seeing through very clearly. I'll probably try polishing them when I get back to working on the boat.

For what it's worth..
12-06-2009 07:39 PM
GaryHLucas I'm using the old windows as a template, just route around around the outside with a flushcut bit and drill through the existing holes. All the existing holes were properly oversized. McMaster Carr sells ruber washers in any size or elastomer you could want, neoprene, EPDM, even Viton. EPDM has the best weather resistance I believe.

Gary H. Lucas
12-06-2009 07:14 PM
mitiempo Gary
Remember to overdrill the holes. A neighbor in my Marina has redone most everything on his Beneteau including the windows. He is using a soft washer under the bolts that is "T" shaped when looking fron its side. The hole in the plexi is just large enough for the washer and the bolt a good fit inside the washer. I asked where he got them and he said they were original from Beneteau, but it looks like a good idea, must be able to source them somewhere.
12-06-2009 06:58 PM
GaryHLucas I am making a new set of bolt in place windows as we speak. The old ones were leaking, I removed them last week. I can see why, they were sealed with butyl tape. The plexiglas was bowed in at the bolts while the fiberglass bowed out at the bolts, leaving gaps beteen bolts. The Pan head bolts though had rubber washers under the heads, which seemed like a good idea.

I am most concerned about the seal around the windows though. In a previous career I researched sealing thing that have to have lots of room for expansion (aluminum against concrete) Everything I could find on the subject from the manuafacturers was moslty concerned with having the sealant THICKER than the motion needed. For silicone the sealant can take a motion equal to its thickness in any direction without it breaking loose. So my plan is to pad the windows out away from the hull using 1/8" rubber washers. Then I'll run a nice bead all the way around the plexiglass to form the seal. This should alow the window to move yet never break the seal. A fillet bead around the edge of a plexiglas sheet doesn't work because when the plexiglass moves it shears the sealant off.

I'll let you all know in about 5 years if it works!

Gary H. Lucas
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