Acrylic or polycarbonate?

snowleopard

snowleopard

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I know acrylic tends to craze and polycarbonate fogs as a result of UV exposure, also polycarbonate is better at impact resistance.

In practical terms, what are the relative benefits for boat windows? Which lasts longer? Which is more scratch resistant? Has anyone lived with polycarbonate windows for a long time? My acrylic windows are starting to form cracks running in from the edge after 14 years.
 
snowleopard said:
I know acrylic tends to craze and polycarbonate fogs as a result of UV exposure, also polycarbonate is better at impact resistance.

In practical terms, what are the relative benefits for boat windows? Which lasts longer? Which is more scratch resistant? Has anyone lived with polycarbonate windows for a long time? My acrylic windows are starting to form cracks running in from the edge after 14 years.
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Yes. Polycarbonate far superior to acrylic for the reasons you mention. Although it is softer on the surface and more easily scratched, in all other respects - strength, crazing (lack of) and clarity of tinting it is better.
 
Polycarbonate is better at impact resistance essentially because it flexes to absorb energy. This is good if you're getting shot at, but less useful on a boat.

The material is much softer and scratch-prone. It is inherently less UV resistant than acrylic, often relying on coatings to achieve UV resistance which degrade, especially if bent round corners. The flexing also makes it much harder to seal than acrylic.

Look, I work for Lewmar and so feel I have decent knowledge of this. I know the skeptics amongst you will say that acrylic is used by ourselves, Goiot, Gebo, Bomar etc. because it's the cheaper material. I can tell you that's not the case, we use it because it's the best material for the application (excepting mineral glass).

Your acrylic windows seem to have lasted OK for 14 years. My steer to you is that you will be replacing polycarbonate windows well within that period, despite having spent a fair chunk more on them initially.

My 2p.

Ben
 
I recently replaced my doghouse/wheelhouse windows using both acrylic and polycarbonate. The two side windows were acrylic about 4ft x2ft in 6mm and the front about 5ft x 33" in 6mm polycarbonate. I am really pleased with the acrylic side windows-totally clear and no scratches or marks. On the other hand the front window in polycarbonate is already (after only 4 months ) showing signs of scratching, and I have been very careful with it, it is not quite and clear as the acrylic and being a largish piece there is a small amount of light reflection when viewed from an acute angle. This may be because I used 6mm rather than 8 or 10 mm. It is quite flexible as it will bend a little if pressed however the original 6mm perspex was quite rigid and perfectly adequate for the job for 39 years!

I find cobolts comments interesting as I was sucked into the belief that polycarbonate was far superior to acrylic but I now regret choosing polycarbonate over
acrylic for my screen and certainly in the future if I replace any windows it will be with acrylic. I suppose the key issue is whether the location of the window is safety critical and whether the boat is at risk if a window fails. If that is the case eg the forward facing windows on an ocean going boat then I suppose the issues of polycarbonate scratching etc becomes minor compared to the unbreakability of the poycarbonate material.
 
cobolt said:
Polycarbonate is better at impact resistance essentially because it flexes to absorb energy. This is good if you're getting shot at, but less useful on a boat.

The material is much softer and scratch-prone. It is inherently less UV resistant than acrylic, often relying on coatings to achieve UV resistance which degrade, especially if bent round corners. The flexing also makes it much harder to seal than acrylic.

Look, I work for Lewmar and so feel I have decent knowledge of this. I know the skeptics amongst you will say that acrylic is used by ourselves, Goiot, Gebo, Bomar etc. because it's the cheaper material. I can tell you that's not the case, we use it because it's the best material for the application (excepting mineral glass).

Your acrylic windows seem to have lasted OK for 14 years. My steer to you is that you will be replacing polycarbonate windows well within that period, despite having spent a fair chunk more on them initially.

My 2p.

Ben
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Thanks Ben.... don't be afraid of sharing your expertise... as long as you are open about your affiliations (which you have been), then your knowledge is most appreciated!
 
cobolt said:
Look, I work for Lewmar
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A question for you, or rather 2.

I bought some of your hatches that were old stock. They have crazed while the windows fitted at the same time have not - does acrylic age in the packaging? And how come you don't do re-glazing?
 
What about glass?

The doghouse window directly in front of the helm seat tends to fog as a result of micro scratches etc. I didn't use glass because of the risk of it shattering if a flying block hits it. In fact one of the acrylic ones smashed when a block failed in an over-enthusiastic gybe.

Anyone have experience of toughened/laminated glass windows?

And while we're at it, I didn't fit wipers as the mainsheet sweeps across the front of the wheelhouse. Is there a way of avoiding getting the sheet round the wiper and ripping it off?
 
Crazing is predominantly caused by UV, hatches due to their position typically see much more than port lights.

2nd cause is cleaning chemicals. Hatches tend to get covered in the same stuff as the teak / deck around them. Actually this chemical damage effect is probably the primary cause of crazing.

3rd cause is bending/stressing. Hatches tend to get trodden on / dinghies loaded on top of them etc.

You don't state the age of the hatches but if you feel they have crazed very prematurely then feel free to PM me and I can investigate.

We offer replacement acrylics for low profile, medium profile, flush and all our opening Portlight products.

In fact the only things we don't offer acrylics for are Ocean hatches and any fixed lights. Previous generation products tended to have bonded in acrylic panels. You are correct we don't offer re-glazing for these. However, both Seaclear and Eagle Boat Windows do a great job in the aftermarket with those services. We simply wouldn't be able to be as competitive as those guys.




snowleopard said:
A question for you, or rather 2.

I bought some of your hatches that were old stock. They have crazed while the windows fitted at the same time have not - does acrylic age in the packaging? And how come you don't do re-glazing?
Click to expand...
 
snowleopard said:
I know acrylic tends to craze and polycarbonate fogs as a result of UV exposure, also polycarbonate is better at impact resistance.

In practical terms, what are the relative benefits for boat windows? Which lasts longer? Which is more scratch resistant? Has anyone lived with polycarbonate windows for a long time? My acrylic windows are starting to form cracks running in from the edge after 14 years.
Click to expand...

Our boat has polycarb windows, fitted by previous owner for trans-atlantic cruise, their advise was to clean with Brasso when they fog, 24 years on and they are still fine.

Brian
 
What about that stuff they use for iPhone screens.
It seems to be hard wearing unless you drop it.
Are you likely to drop a window?
 
cobolt said:
Crazing is predominantly caused by UV, hatches due to their position typically see much more than port lights.
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My hatches (not windows though) are crazed. I can live with the scattering of the light this causes as long as they're not weakened significantly. Are they?
 
Polycarbonate is without doubt technically superior to acrylic in both impact strength and temperature resistance, there are also many other reasons to specify PC over PMMA. However most of those reasons are application specific and unless superior impact strength is required then for boat windows acrylic is the way to go. There are Impact Modified grades available (PERSPEX IM30 & IM50), they don't have the same clarity but do offer increased impact resistance. UV is your biggest enemy and special grades of UV stabilised materials are available, some have surface coatings and others are modified at polymer level, these are not readily available and are very expensive. Minor scratches are easy to remove from acrylics and for this application is in itself a good reason to choose it over PC!
 
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snowleopard said:
I can hardly claim premature failure as they were bought as old stock in 1999!
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OK, well those service companies above will come in useful when you decide to refurb :)

@JimC - surface crazing will not cause any noticeable structural weakening unless it is extremely bad and can be seen to penetrate into the depth of the acrylic panel. I've yet to hear, after 7 years working here, of anyone's portlights or hatches failing due to excessive crazing. Sometimes, the normal surface crazing you see around can even be polished out with brasso or proper acrylic polish, which gives you an idea of just how shallow to the surface it is.
 
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