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Old 19-06-2008, 12:13   #16
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Brad, I was by no means discounting the value of glass in some applications. I'll repeat, "for pilot houses and in areas where you need good visibility or a scratch free surface" glass may be preferred.
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Old 19-06-2008, 12:27   #17
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Roverhi, the reason that tempered glass has typically been preferred over safety glass for offshore marine applications is that safety glass is nowhere near as strong/impact-resistant as tempered glass. In fact, that is precisely why the glass is 'tempered' in the first place.

As to the safety glass remaining intact/watertight after being shattered, I think you are being a little optimistic: if you have ever had a shattered windshield in a car, you would know that it can be knocked in, plastic sheet and all, with very little pressure.

Yes, tempered glass is going to be more expensive to replace - but it is also much less likely to ever need replacement.

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Old 19-06-2008, 16:01   #18
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Laminated glass should not be used unless it is tempered glass laminated which is very expensive. In the regions I have worked in surveyors will not allow plain laminated glass in commercial vessels. As being said, if glass it should be tempered glass.

The main problem with laminated glass is that it is weak - it is in fact weaker than the plain glass it is made from if the plain glass was the same thickness as the laminate because part of the thickness of the laminate is the weak plastic interlayer. The other problem is when it does break, even though the pieces are usually held together by the plastic interlayer they are still sharp.

I did quite alot of work on this in the past following accidents on older inshore fishing vessels without tempered glass (a problem because there is no easy way for surveyors to identify the glass in older vessels - on newer ones they can rely on the fact that correct tempered panes will have the manufacturer's fused standards compliance mark in the corner). These included non toughened glass wheelhouse windows being stove in and was believed to be the reason several vessels were lost.

We have had Lewmar (so acrylic) portlights and hatches in our boat for 12 years and we have a high UV climate here (skin cancer is a serious health issue, for example) and we have no crazing whatsoever except a little on the outside surface of the opening portlight and hatch directly over the cooker in the galley. I suspect their venting of the cooking vapours has affected their UV resistance as there is also a fixed portlight there which has no UV damage at all.
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Old 20-06-2008, 02:01   #19
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I have Toughened Glass for the Pilot house windows. It is equal in strength to 100mm thick of ordinary glass. I lost the genoa sheet one day. It took the car and a chunk of track clean out of the deck. The car then was the whipped a couple of times into one of the windows till I could get it under control. The bangs it made were really horrifically loud and the window remained in one piece fortunately.
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Old 20-06-2008, 10:17   #20
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I have Toughened Glass for the Pilot house windows. It is equal in strength to 100mm thick of ordinary glass. I lost the genoa sheet one day. It took the car and a chunk of track clean out of the deck. The car then was the whipped a couple of times into one of the windows till I could get it under control. The bangs it made were really horrifically loud and the window remained in one piece fortunately.
Quite a testimonial Alan. Can you let us know what size windows you have and what thickness the glass is?

Concerning safety glass, in my time as a paramedic I was expsed to a lot of broken windshields. As stated above, once broken you get a sheet of very sharp shards held together with plastic. It was usually a simple matter to push the winshield from it's frame once the glass had shattered. I imagine if a wave struck a safety glass window with enough force to break it it would also open a large hole.

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Old 21-06-2008, 00:23   #21
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I assume they are 10mm. The glass guy said they are equal to 10x the thickness in ordinary glass. I think they would be about 500x600mm.
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Old 25-06-2008, 18:08   #22
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I have 6, 8" and 4, 6" round port lights with 3/8" tempered glass. If one gets broken, I'll replaced it with glass. I don't like to trust clear plastics to keep water out of my boat. I can get replacements for $90.

That said, I have 1/2" acrylic on my companionway hatch - it's at least ten years old and not quite "clear". If it breaks, I'll replace it with acrylic as I don't trust glass that big to be vertical without protection. Plus I have teak slats screwed to it so as to stay on my feet while furling; a bit impossible to screw into glass.

Fair leads,
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Old 25-06-2008, 20:54   #23
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Thanks Alan,

My windows will be approximately the same size as yours. That helps in deciding how thick they will be. The equivalent of 100mm thick glass gives a good feeling for the strength.

Mike
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Old 26-06-2008, 04:30   #24
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Quote:
Originally Posted by Alan Wheeler View Post
I assume they are 10mm. The glass guy said they are equal to 10x the thickness in ordinary glass. I think they would be about 500x600mm.
Toughened or Tempered glass is stronger and has much greater impact resistance than normal “Annealed” glass. As a generalization, toughened glass is mechanically about five times stronger than non-toughened glass of the same thickness. Since strength is measured in various ways, no one absolute figure can be given.

It is often quoted as being from two up to ten times as strong* as annealed glass, depending on the manufacturing process and how this extra strength is measured.

Tempered glass actually has a softer surface than annealed glass and is slightly more susceptible to scratching.

* ie: From the National Research Council of Canada:
Glass can be greatly strengthened by development of a "stressed skin" sandwich, where both surfaces are in compression and the middle is in tension. This can be accomplished by heating the glass to near its melting point and rapidly cooling both surfaces. The contraction of the middle (of the thickness) of the sheet develops the desired stress on final cooling. Safety Toughened Glass, as it is called, is three to five times more resistant to failure by bending, impact or thermal shock than annealed glass of the same thickness, although other properties such as durability, transparency (except for polarized light), elasticity, flexibility or coefficient of expansion are not changed. The "Achilles Heel" of safety toughened glass is its edges; even a relatively light impact with a sharp object can cause failure. Exterior doors of safety toughened glass are normally protected by metal at the sill because of this. Toughening of glass must be done after it has been cut to size, because any cut or failure results in complete disintegration of the sheet into many small cubes.
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Old 02-07-2008, 09:14   #25
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a good coating of simonize wax yearly would go a long way
I got the name of the cleaner/wax that we recommend for our cast acrylic. Novus Plastic Polish is the product and it comes in many variations.

novuspolish
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Old 13-01-2009, 22:42   #26
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I use laminated/ tempered safety glass in the wheelhouse of my commercial lobster boat and I am in the plastic business!!! Each of the previously mentioned products (glass, lam, tempered, toughened, Acrylic and polycarb) have certain fit and applications. Check with your builder or a good NMMA certified installer for the up to date info.

For the majority of recreational boaters using this forum cast acrylic in excess of 9 mm preferably 12 mm will perform just fine. A perfect compromise of strength, durability, ease of installation and longevity. Great care should be used when selecting adhesives, Get the manufactures claims in writing and check, check, check.

As for cleaners, Its the ammonia in windex that breaks down the carbon backed chain in the acrylic causing the crazing to be seen by the naked eye. Any one following my posts must have lived through the long and drawn out explination of how crazing happens. I will not put you through it again, but relize crazing can and will happen. When it does it significantly reduces the strength of your hatches.

Back to cleaners..... walk into your local ship's chandlery, into the isle of lotions and potions and select any pretty bottle that says it is approved for use with acrylic and polycarbonate. You will be ok from a compatabilty perspective but check, check, check. I use a product called Brillianize (used by a-10 pilots in Gulf I). A little hard to get unless you are in Cali but a real nice product.

Waxing with 100% carnuba is ok. Make sure it does not contain amonia check, check, check It will not hurt your acrylic but your insurance man will not like the fact you are waxing large 2 by 2 horizontal surfaces on your deck. Common sence should be your guide here.

Good luck

Tony "Hatchmaster" D'Andrea
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Old 14-01-2009, 05:51   #27
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I have had some local crazing in my acrylic windows, and always suspected it was due to wiping them with a paint thinner soaked rag when cleaning up a varnish spill. It took a few years, but the crazing got bad enough that I had to replace the window.

For the experts, can you confirm that solvents like paint thinner can cause crazing, and give a list of other things to keep away from the hatches and windows??
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Old 14-01-2009, 05:55   #28
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DO NOT USE ketones, aromatics, esters, halogens, window cleaning sprays, alcohol, kitchen scouring compounds, or solvents (such as acetone, benzene, gasoline, carbon tetrachloride, or thinners). Do not use ammonia based cleaning solutions on the acrylic as it will eat into the sheet and cause it to craze.
Goto:
Care and Cleaning of Plexiglas acrylic sheet
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Old 14-01-2009, 10:20   #29
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Chemical compatibility of Acrylic is a well researched subject.

Check out the attached link. This is current information from CYRO/ Evonik. You may find it useful.

http://www.hydrosight.com/pdf/acryli...resistance.pdf

Tony "Hatchmasters" D'Andrea
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Old 14-01-2009, 20:43   #30
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When I took my Lewmar Portlight into our local plastics shop, the owner took one look at it and said "that's from cleaners". Just use mild soap and water on them.
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