What plastic for windows?

[john_morris_uk]

My daughter needs to replace (she and her dad in reality) the windows in her Pandora 700. We’ve got the old ones off and she’s patiently cleaned up the frames. I’ve sourced some new trim to go on the raw GRP edge and I now need to order some clear Perspex. Except is it Perspex that I need? Or is Perspex the same as acrylic? There’s a slight curve to them so that rules out toughened glass (I’m not matching up curves and having bits of glass made specially and the. having them toughened for a boat that cost a few hundred £!)

The ones that have come off are cracked and scratched etc. I’ve no experience of this, so what’s the best material to replace them with?

Each side is about 120 x 45 cm’s.

 

[Neeves]

Are you sure of those dimensions - the Pandora's I recall had long narrow windows (but my memory may be wrong).

I think you want acrylic.

I never studies the windows in the Pandora - did it come in a frame or were they simply 'glued' in?

Jonathan

 

[prv]

Perspex is a brand of acrylic. Your choices are basically acrylic or polycarbonate.

My understanding is that polycarbonate is more susceptible to surface scratches (although my polycarbonate washboards have been thrown in and out of the cockpit locker for years now without obvious damage) and acrylic is more likely to actually break if hit hard enough. Personally I'd pick polycarbonate for windows, but loads have been done in acrylic over the decades and perhaps it doesn't really matter all that much.

Pete

 

[john_morris_uk]

Are you sure of those dimensions - the Pandora's I recall had long narrow windows (but my memory may be wrong).

I think you want acrylic.

I never studies the windows in the Pandora - did it come in a frame or were they simply 'glued' in?

Jonathan

No I’m not sure. I had a major op over two weeks ago and then went down with an infection three days ago, temp spiked to 40 and I nearly got readmitted to hospital. I’m posting from my phone still in bed! (And that was more information than you asked for!)

You’re quite right that they’re long and narrow. Perhaps I was remembering thinking I could cut both sides out of 1.2 metres by 500 mm?

 

[john_morris_uk]

Regarding the frame question. There’s a rebate in the GRP moulding that’s deep enough to allow a trim to be clipped over (to tidy up appearance from the inside) and for the acrylic to nestle in (bedded on a suitable sealant/mastic. Then there’s a Black GRP moulded trim with about fifty screws in (thank you Makita drill acting as a powered screwdriver). This is also bedded onto more mastic/sealant.

I’m debating whether to use butyl (cheap and comes recommended) or Sikaflex window sealant that’s designed for exactly this job.

 

[PaulRainbow]

The ones that have come off are cracked and scratched etc. I’ve no experience of this, so what’s the best material to replace them with?

I always use acrylic, Perspex is just a brand name (as already pointed out). Polycarbonate does scratch easier, it is stronger, but i doubt if you'd get anything to break the windows in a Pandora. I was re-wiring a workboat last year and they were taking some acrylic windows out with a large hammer, took a ridiculous amount of bashing to break it and get it out (it was stuck in with Sikaflex).

 

[PaulRainbow]

Regarding the frame question. There’s a rebate in the GRP moulding that’s deep enough to allow a trim to be clipped over (to tidy up appearance from the inside) and for the acrylic to nestle in (bedded on a suitable sealant/mastic. Then there’s a Black GRP moulded trim with about fifty screws in (thank you Makita drill acting as a powered screwdriver). This is also bedded onto more mastic/sealant.

I’m debating whether to use butyl (cheap and comes recommended) or Sikaflex window sealant that’s designed for exactly this job.

Don't want to teach you to suck eggs, but make sure you drill the holes slightly oversize, or the acrylic can crack around the screws.

 

[Neeves]

Acrylic can be bent, but you might need to drill holes so that you can screw in battens to induce the bend, though if the windows are in frames the frames might provide the bend. I note there are 50 screw holes these will allow the bend to be induced. You would need to tighten the screws slowly and in turn, one screw then the opposite one. You might want to part fill the old screw holes, if you are going to use the old holes.

I cannot advise what adhesive you might need - but Sika will have something as will 3M. I have never used butyl. I'd spend the money on the mastic - you don't need leaks. You will need to abrade the 'glass' you choose to provide a key for the mastic. I note there is a trim. As you can 'see' through the 'glass' you will see the mastic underneath - unless the trim covers all the overlap (where the mastic would be applied). Seeing through the windows is important if the substrate is white gel coat as any gaps in the mastic will show through. You will find the mastic instructions detailed - follow them! (again, also, not wanting to teach you to suck eggs!)

You will need to mask the part of the glass where you do not want mastic and mask the surround on the coachroof where you don't want mastic. Its a 2 person job applying the windows - or you get mastic where you do not want it!

When you order up the windows there might be an inside and outside, you will want the edges to be rounded, bull nosed or they will be sharp and 'uncomfortable'. The edges should be gently rounded and polished. But maybe the trim covers this and it is not relevant.

The mastic will squeeze out as you screw the windows down - you then need to clean up before the mastic sets off. Don't think you will replace the windows in an hour!

Its is not difficult - it simply needs patience. It is an excellent part of father/daughter bonding! I don't think is a problem where you are - but don't fit the new windows on a blazing hot day - cooler is better (and obviously not raining).

As Paul says - modern mastics are amazingly strong - you only want to do this once! (for each window)

Jonathan

 

[Blueboatman]

I quite like the French method, one long piece of tinted acrylic , sikaflex , no faffing with dissimilar alloy and stainless and oozy mastics and rubber Insets..easy to lever into place too starting at one end. But you will see the inside bolt/nut ends. Hmmm
Worth doodling over a side elevation photo of the topsides to see if it looks good?

 

[TernVI]

Polycarbonate is available with UV-resistant coatings, commonly used for windows. The multi-layer conservatory roof stuff is UV coated.
Also availabe with anti-scratch coatings, used to motorcylce visors, machines guards etc
Good plastic is rarely cheap.

 

[rogerthebodger]

My previous boat had UV resistant coated polycarbonate and it still when milky in time.

I replaced then all with acrylic/perspex.

Polycarbonate is also more flexible than acrylic so need to be bolted in if large area is to be fitted otherwise polycarbonate could spring out.

 

[C08]

My previous boat had UV resistant coated polycarbonate and it still when milky in time.

I replaced then all with acrylic/perspex.

Polycarbonate is also more flexible than acrylic so need to be bolted in if large area is to be fitted otherwise polycarbonate could spring out.

Me too - my UV resistant polycarbonate wheelhouse front that was expensive went milky after 2 seasons whereas the side windows in Acrylic are still crystal clear after 5 years.

 

[scruff]

Each side is about 120 x 45 cm’s.

... I could cut both sides out of 1.2 metres by 500 mm?

Obvious typo is obvious, but I'd double check the dimensions and the units too before you ordered online. I'd hazard a guess the windows are nearer 5cm deep than 50cm...

When I redid my folkboat windows, which would be a similar sort of size, and curvature, I used 5mm polycarbonate cut by local sign writers from the old windows as templates.

Ended up costing around £50 I seem to remember. It bent to match the curvature of the coach roof fairly easily.

 

[john_morris_uk]

Obvious typo is obvious, but I'd double check the dimensions and the units too before you ordered online. I'd hazard a guess the windows are nearer 5cm deep than 50cm...

When I redid my folkboat windows, which would be a similar sort of size, and curvature, I used 5mm polycarbonate cut by local sign writers from the old windows as templates.

Ended up costing around £50 I seem to remember. It bent to match the curvature of the coach roof fairly easily.

You’re quite right. Each window is slightly tapered with semi-circular ends. Length 105 cm and max height 21 cm narrowing down to 20 cm. I’ve ordered some clear acrylic £43 odd plus VAT and carriage.

All I’ve got to do now (after cutting them out and cleaning up the rebates) is to decide what mastic/sealant to use. Bed them on butyl tape and Sikaflex 295 underneath the frame/clamp trim thing? But then hope I never have to taken them off again!

 

[NormanS]

Butyl tape is delightfully easy to work with.

 

[Iliade]

Bit late now, but looking at googled pictures it looks like they changed the windows between mk 1 pandora and 'international' pandora in the region of the shrouds. If rigging stresses are indeed going through the window, even compressive ones, I'd opt for polycarbonate. Otherwise they are inboard so acrylic should suffice.

 

[mrangry]

I would choose acrylic over polycarbonate and if the windows are mechanically held in place with screws/bolts I would use butyl to seal. It is so much easier to use and less mess and can be dismantled in the future with ease if need be. I would only use an adhesive sealant like sika if the fixings were weak and wished to bond the window in place.

 

[john_morris_uk]

Bit late now, but looking at googled pictures it looks like they changed the windows between mk 1 pandora and 'international' pandora in the region of the shrouds. If rigging stresses are indeed going through the window, even compressive ones, I'd opt for polycarbonate. Otherwise they are inboard so acrylic should suffice.

I don’t believe too much (if any) rigging stress comes up through the windows. Mast compression is transferred via an ‘A’ frame inside the cabin to the hull. Shrouds and fore and aft lowers come down to the side decks not too far from the deck/topside join. The only stress or load transmitted up through the windows would come from the aft lower flexing the deck. The deck doesn’t flex noticeably when walked on. I think a suitably flexible mastic will cope with any tiny movement. Pandora’s are not renowned for their window leaks as far as I’m aware.

 

[john_morris_uk]

I would choose acrylic over polycarbonate and if the windows are mechanically held in place with screws/bolts I would use butyl to seal. It is so much easier to use and less mess and can be dismantled in the future with ease if need be. I would only use an adhesive sealant like sika if the fixings were weak and wished to bond the window in place.

The windows are mechanically trapped in place (in their rebate) by the external window frame. No screws or bolts through the acrylic.

 

[Plum]

My daughter needs to replace (she and her dad in reality) the windows in her Pandora 700. We’ve got the old ones off and she’s patiently cleaned up the frames. I’ve sourced some new trim to go on the raw GRP edge and I now need to order some clear Perspex. Except is it Perspex that I need? Or is Perspex the same as acrylic? There’s a slight curve to them so that rules out toughened glass (I’m not matching up curves and having bits of glass made specially and the. having them toughened for a boat that cost a few hundred £!)

The ones that have come off are cracked and scratched etc. I’ve no experience of this, so what’s the best material to replace them with?

Each side is about 120 x 45 cm’s.

Acrylic is not necessarily better or worse than polycarbonate with respect to UV resistance. It all depends on the specific grade of each. Car headlights are polycarbonate with the vast majority of the manufacturers using uv resistant grades. Just because an acrylic supplier says their product is uv resistant, will they guarantee it? When I replaced mine i used Perspex brand acrylic as Perspex say "30 year guarantee against outdoor weathering". I purchased from Cut to Size Acrylic (Perspex) Sheet, Tube & Rod - Simply Plastic

www.solocoastalsailing.co.uk