Do I need to put curve on replacement windows?

[Samoddie]

Am replacing the port lights in my Anderson 22 (yes, made of unobtainium, etc ). Did one in the summer, which was pretty hard, and took almost all day. I had refixed the frame, but stupidly hadn’t sealed the actual pane into the frame. So, frame was well fixed to the boat, and took an age to get off. All told, it took a day to do the one pane (my objective had really been to see how thick the acrylic was, but I wasn’t able to resist rebedding the pane and frame. Am expecting that one remaining frame will be as hard to get off, and the port side much easier cos they wont be at all well sealed once I have the fixings undone. The old acrylic was 4.5mm thick, and based on what I have read I have come to the view that 6mm will likely be fine (unsupported vertical span is perhaps 180mm). One reason I am not going for thicker is that the lights curve a little fore/ aft. My main question is - do I need to apply heat to allow this tiny bit of curve in the acrylic? Or, if the acrylic easily adapts to the shape, will it fine to put the acrylic into the frame, and re bed this frame into the cabin side? Subsidiary questions - I used Sikaflex to both bed acrylic into frame and to seal the frame to the cabin side. On the other hand, it does seem as if people use either specialist butyl products, or even just plain butyl tape? Comments welcome on all these issues! The complicating factor is that I will be doing the work in Feb, on the W coast of Scottish Highlands so while it wont be freezing, it wont be warm. At least when I do the next 3 portlights, the boat wont be afloat!

 

[Rum Run]

Hello Sam, I also have an Anderson 22. If you ask on the Facebook group you might get an answer from Andy Lawson who has lots of experience of most jobs on the boat - I haven't done this yet so don't know the details of sealing. I have done plenty of other acrylic work though.
Nominal 4mm cast acrylic is likely to be about 4.5mm and should curve to fit OK cold. Proper heat draping of acrylic needs a big oven and a bespoke drape-mould, which I don't imagine Anderson Rigden and Perkins of Whitstable had in the mid 70's.
Maybe worth keeping over 15°C though; maybe some blankets and a hot-water bottle wrapped around until you are ready to do the final fit. Or in the car with the heater running full blast.
Best of luck from the Essex coast....

 

[Neeves]

Maybe worth keeping over 15°C though; maybe some blankets and a hot-water bottle wrapped around until you are ready to do the final fit.

Presumably for Scotland you mean 'and a hot water bottle wrapped round at your midriff.....'

 

[Rum Run]

Presumably for Scotland you mean 'and a hot water bottle wrapped round at your midriff.....'

I was thinking of the acrylic panels, but thinking about it again, an extra one for personal use would definitely make the job go easier for this Southern softy.

 

[Neeves]

And I forgot to mention

Most adhesive/sealant suppliers have formulations specifically for sealing windows (the market in the construction industry is much bigger than marine). I know 3M had a sealant, it was the original used on our catamaran - but forget the 'name' and I am sure Sika will have a specialist product. They also will have detailed instructions on application. We used a product under the brand name Fixtech, or Fixtec, and they supplied me with chapter and verse on application, but I think they are only local, to Australia. The problems here are high, not low, temperatures. They specifically emphasised the impact of temperature and thickness of the 'film' (both of which will, or may, vary with the formulation chemistry).

Jonathan

 

[Daverw]

I did one on our boat with a shallow curve a few years ago, did it in the summer sun and used a hot air gun to slightly raise the temp, not enough to damage the surface but it then easily curved, cooled off very quickly and shape was set, then glued / sealed it on, curving first then fitting saved loads of mess.