Acrylic Windows vs. Toughened glass

[global_odyssey]

I've replaced Alk's aluminium framed 5mm toughened glass windows with custom-made 10mm acrylic ones. This is only because the old frames were so well attached that they were damaged and bent during removal.

The new ones are CNC machined with a 3mm rebate around the inner edge (and 4mm chamfered outer edge), then sanded and annealed to relieve stresses before painting the rebate with a 2-pack acrylic silver paint to simulate a frame - which then hides the 3mm foam gasket seal. They are fitted with A4 Interscrew-type fasteners/M5 pan-heads/washers.

They look great (the acrylic apparently has a 10 year UV guarantee).

... But are they strong enough for serious offshore work?

Are there any "rules" about windows and materials?

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[tcm]

um, i suppose this is a bit late? I wd have conducted careful stress measuring tests first of all, probably involving a hammer. I would guess 10mm acrylic is a whole heap stronger than 5mm glass. But the acrylic risks becoming dull over time , so it is imperative that you hardly wash the boat at all. Quite a result, really.

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[MainlySteam]

Most production hatches/ports are acrylic (look at Lewmar for example) and are ok offshore.

We have acrylic for hatches and opening ports (as they are Lewmar) and toughened glass for fixed. The acrylic is standing up ok after 7 years with very little marking - I think because as TCM suggests don't clean it unless you really have to, then only with a very soft brush (if dirt won't hose off, leave it, it will come off by itself sooner or later - rubbing it off will only risk scratches).

John

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[BarryH]

Without drifting the thread too much, you can buy a neat little acrylic polishing kit from M&P motorcycle supplies. Cheaper than the stuff you buy in the swindlries and it gives brilliant results. Takes all the scratches and haze out. Costs about a tennner with the mops and soaps. Will do hatches and stuff on a boats loads of times.

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[MainlySteam]

Thanks Barry - I will have a look in some MoBike places out here (NZ), see if anything similar.

John

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[global_odyssey]

Thanks chaps.

The 'prototype' acrylic window was actually bashed over the edge of a metal skip before committing to it. It did not break under some severe punishment but I wasn't brave enough to push it to destruction, fearing possible mutilation if it disintegrated into flying shards.
I imagine glass would have broken under the same punishment.

My main concern is that in time (with UV degradation, sctartching, etc) the windows will probably craze and lose their mechanical strength.
But hey, if they last 5 or 10 years I can get then get some new ones made.

I sailed on a boat this season with acrylic windows which had gone opaque, although with no crazing. The owner was going to replace them completely. However, on close inspection, only the outer surface had degraded. A quick rub with 'Brasso' and a soft cloth brought them up a treat and in less than an hour all 8 windows were clear and see-through again.

That saved a few quid!




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[Talbot]

My acrylic windows became exceedingly brittle over time. That also were susceptible to cracks and crazed. I replaced them with polycarbonate which is supposed to be much stronger for the same weight. Main drawback is that they do scratch more easily than the acrylic, and they also bend a bit more easily. They make bullet proof windows out of polycarbonate so it takes imact much better than the acrylic.

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[global_odyssey]

How long did they take to go brittle (i.e how old were they?).
Some acrylic is not UV stavble and will degrade more quickly.

Polycarb is strong but can be very susceptible to attack from some solvents.

My advice is to clean any plastic windows with plenty of clean water and a soft cloth only.

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