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Old 12-28-2012, 12:43 PM   #21
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That sure runs counter to everything I've been told about Lexan by one of the top plastics company in Seattle, TAP, Inc.. When talking to them about replacing our venturi panels they strongly recommended against Lexan. Lexan is stronger than Plexiglas, they said, but it is far more susceptible to scratching than Plexiglas.

For windows on a boat, they said, they always recommend laminated safety glass. For venturi panels, they always recommend Plexiglas.

And, they said, both Lexan and Plexiglas will scratch very quickly if wipers are run over them. Lexan will scratch sooner and worse than Plex but both of them will develop scratches very quickly, particularly if the wipers pick up any dirt.

The Margard coating, they told me recently, while it can hold scratching at bay for awhile, does not prevent scratching in the long run. Even the Margard literature only claims "may" help prevent scratching.
Hard to argue with "experts" but experts most always have an incentive to say what they say. I can only speak from my experience. My 1/2" MarGard Lexan windows have been in place 10+ years with wipers on all 3, the boat is a wet boat so wipers are run often, there are no marks from the wipers, the side windows sweat and fog (safety plate) the Lexan windshields do not.
I made the curved windows on my Willard of regular Lexan-UV (MarGard won't bend tightly) also the ventiri screens. The PO said he had replaced these plexiglas parts twice because they turned yellow in the FL sun. I replaced them in '07 and they are still clear.

Maybe TAP doesn't sell or stock MarGard, that would be all the incentive they need to recommend against it...
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Old 12-28-2012, 03:39 PM   #22
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We are new to this boat. Had this 41' 1981 Defever for about 4 months now. It's alot of new systems to learn about. We've had her out in several wild seas and each time we're impressed with how she handles those squirrely waves that come from several directions. On our last outing we were running a small heater to keep the windows defrosted on the inside and the heat must have been too close and we started a running crack in the front pilots window. #@$%&!!!!! It appears DeFever is no longer in business and we need advice on how to go about replacing this window. Does anyone know of a manufacturer that has the templates for the DeFever? Peggy
Have you tried to seek help at the DeFever Cruisers club? I'm sure some of the members have had similiar problems. DeFever Cruisers - A Club for Yachting Enthusiasts with a Passion for DeFever Vessels and the Cruising Life!
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Old 12-28-2012, 07:17 PM   #23
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Maybe TAP doesn't sell or stock MarGard, that would be all the incentive they need to recommend against it...
They are one of the most experienced plastics experts in the greater Seattle area. If it's plastic or anything to do with plastic, they work with it including making big custom curved flying bridge venturies for yachts.

I don't question your experience with Lexan and MarGard. But since the boat manufacturers use laminated safety glass, which in our case has not scratched with wiper use for 40 years, and a top plastics company recommends against Lexan (and plexiglas) for any applications where abrasion is a potential problem, particularly Lexan even with MarGard, I think I'll stick with laminated safety glass for all the windows in our boat and will continue to recommend the same whenever anyone asks.
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Old 12-28-2012, 07:38 PM   #24
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Google is your friend guys. According to this there are different "grades" of Margard so possibly you both are right.

I'm fascinated by this discussion. The glass in our centre window is scratched from the wipers. I'm not anxious to go to the effort to replace it but the possibility of getting something that wouldn't fog up as much in our winter boating is appealing.
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Old 12-28-2012, 09:35 PM   #25
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bobofthenorth, Thanks. I'm quite sure I used the MR-5 grade (lower grade) which was all that was available at the time where I got it.

I might use laminated safety glass for side windows but I don't think its impact resistance is any greater than plate glass. Forward facing glass should be tempered glass or polycarbonate (Lexan). All window manufacturers use tempered glass. The non-fogging is a nice bonus but the main thing is the strength.
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Old 12-29-2012, 12:13 AM   #26
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That's backwards. Safety laminated glass should face forward, and probably be used on the sides too. It is stronger, but if that breaks with a wave, you'll have thousands of little pieces of glass on the deck and a complete hole waiting for the next wave.
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Old 12-29-2012, 12:19 AM   #27
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That's backwards. Safety laminated glass should face forward, and probably be used on the sides too.
Agreed, and so do the boat manufacturers.
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Old 12-29-2012, 07:23 AM   #28
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Greetings,
Um, I think we're a bit mixed up. TEMPERED glass will break into thousands of pieces and leave a gaping "hole". LAMINATED glass will break but, depending on the robustness and size of the frame, will remain intact, due to the layer of plastic between the glass layers, for the purposes of keeping the "hole" closed. Now, evidently there is tempered AND laminated glass on the market together in one product. No idea how THAT would work. One of the reasons a lot of manufacturers are going with tempered glass all around is that it's CHEAPER, not necessarily better or safer.
For example, your car has laminated glass on the windshield and tempered glass on the remaining.
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Old 12-29-2012, 09:56 AM   #29
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Greetings,
Um, I think we're a bit mixed up. TEMPERED glass will break into thousands of pieces and leave a gaping "hole". LAMINATED glass will break but, depending on the robustness and size of the frame, will remain intact, due to the layer of plastic between the glass layers, for the purposes of keeping the "hole" closed. Now, evidently there is tempered AND laminated glass on the market together in one product. No idea how THAT would work. One of the reasons a lot of manufacturers are going with tempered glass all around is that it's CHEAPER, not necessarily better or safer.
For example, your car has laminated glass on the windshield and tempered glass on the remaining.
I agree with RT on this. On a building extension I did on a childcare centre we had to quote and install safety glass that would break but not shatter or splinter in to shards. The company that did the glazing installed a window tint type liner on top of a standard glass window that enabled the glass to meet the Aust. Standards for safety glass.

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Old 12-29-2012, 10:28 AM   #30
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A couple of points, some already made but need restating.

1. The front windows in LRC's are designed to take a wave directly and survive. I find it difficult to understand how the window would have cracked. But differential temperatures can place some serious forces on the material.

2. Someone already beat me to it, and that is to contact the Defever Cruising Club. They are a good bunch of people with specific knowledge about Defevers.

3. Contact North Harbor Diesel, they are experienced with working on these type of vessels and can be a great resource for knowledge and parts. They are great people and will help you not only find the parts but provide the knowledge to replace the window properly. North Harbor Diesel

Always loved the 49 Defever. All the best hope this helps.
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Old 12-29-2012, 10:37 AM   #31
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You relly don't need to buy the window from Defever or any specialized supplier. You will need to pull the window, take it to your local glass company and have them determine which is best suited for your needs. They should be able to use the old glass as a pattern and cut you a new one. We had 3 windows in our Marine Trader replaced this way. It was simple and relatively inexpensive. See our posts,
The Trawler Beach House: Leaking Window Repair Update

Hope this helps. Chuck
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Old 12-29-2012, 11:02 AM   #32
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Greetings,
I think Mr. PC has stated the reason for the crack in this case-differential temperatures ie: thermal stress. Glass is a wondrous material but will break due to stress or strain. ANY surface or edge defect (flaw) is a potential site for crack propagation. It could be that the window frame was a bit tight or off level and the added heat simply exacerbated the existing flaw thus generating a crack. I would replace the offending panel with laminated glass as opposed to tempered.
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Old 12-29-2012, 04:44 PM   #33
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Sorry, I forgot to put "tempered" in my comment about breaking into lots of pieces.

Another thing to know about tempered glass is that it cannot be cut. A regular piece of glass has to be cut, then sent off to be tempered. This will add some time to the process vs. just going down to the glass shop and getting something cut to size. If you try to cut a piece of tempered glass, it'll probably explode on you. Don't ask me how I know this. :-)
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Old 12-29-2012, 06:15 PM   #34
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Don't ask me how I know this. :-)
Hahaha ohhh do tell hahaha

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