Replacing 34-Year-Old Windows on My Hunter Horizon 23
Published 2026-10-04
There are some jobs on an old boat that you know are coming eventually. You can keep an eye on them, convince yourself they have another season left in them, and generally avoid disturbing something that has managed perfectly well for decades.
The windows on my Hunter Horizon 23, Vixen, were one of those jobs.
They were the original dark-grey Perspex windows fitted when the boat was built in 1992, and after more than three decades they were showing their age. Both sides were heavily crazed, the acrylic covered with a network of fine cracks.
Then the starboard window cracked from top to bottom.
That rather settled the matter.
The original acrylic was heavily crazed after 34 years.
I ordered a replacement pair from Hadlow Marine. They supplied new 6 mm Perspex windows in dark grey, matching the original colour, with bevelled edges and all the fixing holes already drilled. The holes were slightly oversized to allow the Perspex to expand and contract naturally.
The kit also included Scapa 3507 bedding sheet and a complete set of new fixings: M5 16 mm backing screws with 10 mm interscrews. The whole package cost £358, with another £10 spent on drill bits, masking tape and a scalpel. Hadlow also publish fitting instructions for using the Scapa bedding system, which I followed.
I knew removing windows that had been attached to the boat for 34 years had the potential to become one of those jobs that starts innocently and then occupies the entire weekend. Before touching any of the fixings, I marked around the existing window and covered the surrounding coachroof with masking tape. It would make removing the old bedding and cleaning up around the window much easier.
Blue masking tape marks the outline of the original window.
With the original self-tapping screws removed, it was time to find out just how firmly the 1992 windows were attached to the boat.
To my surprise, the answer was: not especially firmly.
The windows had been fitted over what appeared to be some kind of double-sided foam or fabric-backed gasket. Decades of compression had flattened it considerably, but it hadn't turned into an immovable mass. With some careful levering, the Perspex began to come away from the coachroof.
The acrylic itself was another matter. The old windows did not exactly come off in one elegant piece: the crazed material broke apart during removal. By that point, though, preservation was hardly the objective.
The old window removed, exposing the compressed bedding around the coachroof openings.
What was left behind looked worse than it really was. The original gasket material clung to parts of the coachroof, but most of it came away with a screwdriver and some light scraping. Once the bulk had been removed, I went over the surface with 120-grit sandpaper, simply to take down the remaining high spots and leave a reasonably smooth surface.
Finally, I wiped the whole area down with alcohol. Conveniently, that's something I already carry aboard because I use it in the boat's stove.
The open cabin window apertures after removal of the old Perspex.
The original windows had been held on with self-tapping screws. The replacements use machine screws and interscrews, so the existing holes in the coachroof needed opening up. I drilled them to 7 mm with a metal drill bit, then added roughly a millimetre of countersink to the outside edge of each hole.
The countersink wasn't there to hide the fixing. I wanted to take the sharp edge off the gelcoat around the hole to help prevent cracking. There was no need to touch the Perspex itself: Hadlow had already drilled those holes and allowed a little clearance for thermal expansion.
Then came the part of the installation that was quite different from the conventional tube-of-sealant approach.
The Scapa 3507 comes as a sheet. Instead of trying to cut a gasket to exactly match the perimeter of the window beforehand, I covered the entire aperture. The new window then went over the top of it, ready for the surplus material to be trimmed away once it was fitted.
The method relies on compressing the Scapa by around 30 per cent to form the waterproof seal, without an additional bead of sealant around the outside. That appealed to me for another reason too: the window is bedded rather than permanently bonded, so it can be removed and refitted later if necessary.
Getting the window onto the boat was straightforward. Getting all the interscrews into position while working alone was initially less so.
Each interscrew has to sit inside the coachroof while its corresponding machine screw is fitted from outside. With another person aboard that would be easy. On my own, it meant persuading small metal fittings to stay exactly where I wanted them while I went back outside.
Then I realised I was making the problem much harder than it needed to be.
I could simply push each interscrew into its enlarged hole from inside the cabin and put a piece of masking tape over the back of it. The tape held the fitting in place while I went outside. It was one of those very simple solutions that, once you've thought of it, makes you wonder why you spent any time doing it the difficult way.
A close-up of the new interscrew fixings inside the cabin.
With the fittings held in place, the actual installation became surprisingly easy. I fitted one screw first and used it as a pivot point. The new window could then move slightly while I lined up the remaining holes one at a time.
The replacement windows were a perfect fit. No specialist equipment was needed either. Getting some of the interscrews into their holes required reasonably nimble fingers, but that was about the worst of it.
This isn't a job for maximum torque. I tightened the screws just enough to compress the Scapa bedding and make the seal, without putting unnecessary stress into the Perspex.
With the window secured, the bedding sheet still covering the aperture could finally be removed. Using a very sharp scalpel, I carefully cut away the material covering the openings, then trimmed the excess around the outside of the window. The result was remarkably neat.
The new dark-grey Perspex window fitted to the coachroof.
The completed window installation viewed from inside the cabin.
The first window — the cracked starboard one — took me around seven hours. That sounds quite a long time for fitting a single piece of Perspex, but much of it was spent learning: discovering how the old window had been installed, cleaning off the bedding material and working out the new fittings.
The port side took about four hours.
Nothing had fundamentally changed. I simply knew what I was doing by then.
Visually, I'm very pleased with them. I deliberately chose dark-grey Perspex because that was the original colour. The new windows retain Vixen's familiar appearance, but the difference compared with the 34-year-old crazed acrylic is enormous. They have made the whole side of the boat look younger.
The opposite cabin window with its new fixings fitted.
Of course, looking good is secondary to the question that matters with any boat window.
Does it leak?
Once both sides were fitted, I tested them with a hose and checked inside. So far, no leaks. Hopefully that's one job I can leave alone for a while.
There is something satisfying about replacing a component that has done its job for more than three decades without changing the character of the boat.
The old windows lasted 34 years. If these manage anything close to that, replacing them will very definitely be somebody else's problem.
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