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Replacing crazed boat portlights

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Stu Davies saved a lot of money by getting new acrylic windows manufactured

Stu Davis’s yacht. Credit: Stu Douglas

I bought my Beneteau 381 14 years ago. The time has passed quickly and we are now in need of replacing some things.

Among them the Lewmar portlight lenses have crazed – as they all eventually do – and look unsightly. The hatchlights are identical.

I looked at the replacement costs of the portlight lenses and found the prices to be rather horrifying: £85-ish for the smaller ones and around £180 for the larger ones.

Portlights that were fitted to my boat, and those of other yachts from the same era and up until about 2000 are known as Old Standard Portlights. The lenses are made out of flat Perspex.

Sealing strip on boat portlights

Sealing strip that has been weathered on the boat’s portlights. Credit: Stu Evans

The newer ones, the Standard Port Light, as my neighbour in Portugal has found out, have part of the latching mechanism moulded into the lens and so they can’t be cut from flat stock Perspex.

They are just as expensive and in his case (he has a Dufour 36 Classic and Dufour apparently had some special sizes commissioned for their boats) replacement lenses are like hen’s teeth now.

In my quest to be a PBO expert, I did some research.

The material we call Perspex is actually acrylic (also known as Polymethyl Methacrylate, PMMA), which is manufactured by many manufacturers in the world.

Perspex and Acryglas are some of the most commonly available brands in the UK.

A laser cutting machine

Westminster Plastics uses a computer controlled laser cutter. Credit: Stu Davis

I’ve known for some years that plastic sign manufacturers can make simple shapes but I’ve found out that their capabilities have moved on in leaps and bounds with the advent of CNC machines and laser cutters.

So I looked to see if the sign makers could make Old Standard Portlights.

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Westminster Plastics in Wrexham Industrial Estate has laser and CNC cutting machines.

After carefully measuring the old lens, (I had an old No4 in my workshop and used this as a template) it is then entered into the computer.

There is no more fear of breaking the plastic while hand drilling and cutting. Beneteaus come with smoked green lenses while some boats use grey.

The basic material was available in the colours I wanted, but my company would need to purchase a full sheet to make just a few small models. So, I chose clear plastic from the stock of the firm.

Sealant on a window

Pull sealant away from the window frame. Credit: Stu Davis

They were cut in one day. They were perfect with beautiful cuts and holes and best of all they only cost £45 each, a big saving on official prices.

It is easy to change the mounting hardware and close it by simply removing bolts and screws. I’m now carefully making tracings of the smaller lenses to have a full set made.

Next, we will be working on the hatchlights.

Seals used to close the lens also degrade.

They’re basically 9mm outside diameter closed-cell neoprene round seals with an arrowhead moulding on one side which slots into the frame’s aluminium housing.

Boat portlights

The new acrylic lens is vastly superior to the previous crazed lens. Credit: Stu. Davies

But these seals are also silly prices – more than £50 just for one.

I already had on the boat some 9mm round closed-cell neoprene sealing material which I’d found on ebay.

When I was a young fitter, I learned this trick from my local steelworks. The seals were essentially large O rings that could be cut and superglued.

So, I took out the old sealant and cleaned the grooves in the frame.

After measuring the new seal, I placed it in the frame and trimmed the edges to match before supergluing them together.

I performed a test run to ensure that the seal would stay in place after applying the sealant. And it worked!

The ‘L’ closing and locking levers were a bit tight at first but a light dusting with talcum powder soon lubricated them enough to get them turning.

Talc (not silicone grease or Vaseline which doesn’t seem to help on plastics) was also applied to the shafts going through the lens and the sealing O-rings which butt against the lenses.

Frame leaks

A gap in the frame of a boat portlight

Leaks can occur when there is a frame gap in the boat portlights. Credit: Stu Davi

My boat’s aluminium portlight frames are in two parts with a horizontal gap on both sides on the exterior.

Over time, the sealing material in these two gaps degrades. Water enters through the internal channels and drips down into the boat.

Sikaflex 291 can be used to reseal these gaps.


Have you enjoyed reading How to replace crazed Boat Portlights?

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