How to bend acrylic

Andy Pag discovers that replacing the curved saloon windows of his Lagoon 410 is far from straightforward

- Andy Pag

The saloon windows on our Lagoon 410, Cushla, have been crazed since we bought her, but listing her for sale made us realise just how ugly they'd become over the last four years, semi-circumnavigating from Europe to New Zealand.

Luckily, we found ourselves with the time and access to materials to tackle the job. But the big challenge was that the windows have a slight curve to them. Over the 700mm width, they bow out by 15mm.

My first thought was that this could probably be curved to shape in the frame and held in place by the strength of the adhesive. A couple of sage boaters advised me that a heat gun would soften it into place, so buoyed with the confidence that this was a job we could do ourselves, we set to work.

First foot forward

I dug away some of the caulk between two of the panes with a blade and, from the inside, cut at the adhesive behind the pane with an oscillating tool, just enough to free up a corner so I could get a pair of calipers around it and measure the thickness; 8mm. I could now order the acrylic I needed while the boat was still waterproof, but 8mm is pretty meaty and although the adhesive might be strong enough to hold it in an arc, without pre-bending the windows it would create internal stresses that would cause the crazing to return prematurely, and put extra pressure on the adhesive bond. I felt the new panes would need to be bent.

I ordered a full sheet of acrylic, 1.2m by 2.4m, and patterned the panes I wanted to replace using out-of-date charts. The weight of the paper makes it an ideal patterning material, and a paper pattern is the only way to measure a curved window onto a flat new sheet of acrylic.