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We're working on converting a boat to live on. It's very old, and one of the things that always fail on boats over time are the windows. Several of ours leak when it rains.
The windows - proper term portholes or portlights, depending on whether you can open them - are made up of a metal frame which holds a pane of toughened glass and is attached into an opening in the hull. All of the parts are bolted together with lots of sealant everywhere to try to stop water getting inside.
We decided to quickly patch up most of the windows before winter and just try repairing one properly to find out how difficult it is. Our practice window was a small, non-opening one we hoped would be easier, faster, and less annoying if we didn't manage to make it seal completely. Quite a bit has been written about rebuilding boat windows, and our experience matches everyone else's: it's a slow, tedious job!
This write up is to help us remember what we did, give anyone curious an idea of what it was like, and pass on what we learned to anyone needing to do the same sort of work.
The frame of the window has two pieces, one outside and one inside the boat. On the outside is the meat of the frame, an extruded aluminium channel that holds the glass, and is sealed and bolted onto the outside of the hull. On the inside there is a much simpler frame made of aluminium sheet, which is just there to spread the load from the inside ends of the bolts.
Both pieces of the frame further divide into four quadrants. The outer frame's quadrants are attached together by little flat strips of aluminium that slot into the end of the extrusion, and are then held in position by friction and a few screws.
Bolts secure the whole frame in the hull, with heads outside and nuts inside, and the bolt going all the way through the outer frame, glass fibre hull, and inner frame. The bolt and head on the outside is fairly standard, a countersunk pan head and a slot for a screwdriver blade. The nut on the inside is a diabolical horror! Instead of a typical hexagonal nut with a threaded hole, they are instead a blank circle on the inside, with a thread hidden underneath. The underside of the nut has some shallow teeth which are supposed to bite into the inner frame and prevent the nut from moving. Unfortunately, after a few decades of corrosion and stress, the teeth no longer grip. More griping about that later on!
A pane of glass is held inside a channel in the outer frame, and is surrounded by sealant that protects it from the hard metal in the frame.
Diagram of the window as seen from outside.
Same diagram as an svg vector drawing.
Same diagram as an svg vector drawing.
This is a slightly idealised version of the process, in practice we did bits of each of these steps in a fairly random order until we figured out how the window was meant to come to pieces. I'll give what turned out to be the correct order here to make this easier to understand!
First, we undid the bolts, one person unscrewing the heads from the outside while the other held the nut inside. Some of them came out without a problem, most needed pliers to hold the nut so it couldn't spin, one only came out after we used a hacksaw blade to cut a slot in the nut to shove a screwdriver into! To anyone considering using this style of blank nut: please, please don't! They're a nightmare. Use something with a hexagonal head or some flat sides so you can grab it and apply enough torque to break however many years of accumulated sealant and corrosion.
With the bolts removed, we could pry the inner frame out. It was stuck because sealant from the outside part of the window has squished its way through to the inner part, and glued the frame to the hull. We did our best not to bend it to badly, but there's only so much you can do to protect a thin piece of metal when you have to pull it off with a crowbar! It wasn't particularly hard to bend back into the right shape afterward.
Then we did something very similar to the outer frame, except it took even longer. First we used a thin, flat steel tool (a spudger) to painstakingly cut/force the sealant away from the hull. Once the frame started to feel loose, we starting pushing a screwdriver and later the crowbar under it, and slowly jiggled it out of the tatters of sealant. The sealant was some sort of white rubbery stuff, it felt fairly hard and tough, and was difficult to cut or remove. I'd guess it was some sort of heavy duty sealant like Sikaflex 291i.
The outer frame holds the glass, so once the frame slid out of the hole in the hull we had one convenient unit we could take somewhere comfortable. We started disassembling the frame by trying to cut the silicone squeezed between the edges of the glass and the inside of the frame. The gap was large and completely filled up with the sealant, so trying to cut through it was very difficult. It felt really satisfying when occasionally big strips of it came off!
Eventually the glass started to feel loose, so we removed the screws holding the quadrants of the frame together. Two of the four joints were badly corroded, to the point that someone seemed to have ground the heads of the screws flat using an angle grinder. The other two joints had screws that were just able undo-able, and that was enough to let us separate the frame into two halves. We then very slowly and carefully wiggled the two sections apart, wedging larger and larger tools into the gap as it grew. The whole process was nerve wracking because the pane of glass was still trapped in the frame, and we had to use a huge amount of force.
Once the frame was in bits, or near enough, we started cleaning things up ready to put back together. Sealant had to be scraped off of the hull, inner frame, outer frame, out of the channels in the outer frame, and off the edges of the glass. It took ages, especially the channels in the outer frame.
Disassembly was by far the longest, most frustrating phase of this project.
Photo of the disassembled, clean parts of the window.
We weren't sure how best to reassemble the window, so this is a record of the guess we made, and we'll see how it copes with life for a little while.
Boat windows are a problem because they have to deal with lots of environmental problems beyond just weather:
We chose to use an extruded rubber seal around the glass, in the hopes that it would be long lasting and less frustrating to dismantle than silicone sealant. We'd then seal the window to the hull using a non-setting butyl sealant, which should be able to better cope with flexing without being as annoying to remove as heavy duty marine sealants are.
The outer frame is an extrusion with a complex set of channels in it. My guess is that these were meant to hold some kind of moulded rubber seal, which has long since disintegrated and been replace with sealant. We couldn't find an exact replacement, so we used a combination of a rubber U-channel that would fill the space between the frame and glass, neoprene foam to fill the gap in bottom of the channel, and silicone sealant to fill the awkward spaces too small to fit rubber of foam in.
Same diagram as an svg vector drawing.
We did a test run of assembling the frame with two layers of foam and a thick U-channel, hoping that the extra thickness would squish everything together and make it seal more reliably. This caused too much friction to be able to slide the two pieces of frame onto the glass, so we gave up. It would probably work on a window that came apart properly into its quadrants, and it turned out that once we'd added the silicone it lubricated everything, which would perhaps have been enough to use the thicker foam and rubber. As things worked out, we used a thinner U-channel and a single layer of foam, and added silicone around the edge of the glass in case the rubber didn't seal very well.
Photo of the rubber U-channel and neoprene strip.
The little strips that hold the quadrants of the outer frame together were very difficult to slide back in. After lots of sweating, we gave in and filed them down a bit so that they fit easily. We also decided to leave the screws out, as we were worried they would succumb to corrosion like the rest already had, and make it impossible to do any future work on this window. The quadrants are still held securely in place by friction and the outer frame being a tight fit through the cutout in the hull.
Photo of the reassembled window ready to go back into the hole in the hull.
There are thin gaps where the quadrants meet which we did our best to fill with silicone. Doing it earlier in the process would have worked a lot better than as an afterthought when we'd already put the window back into the hull!
With everything tidied and rebuilt, we squirted a good thick ring of butyl around the hole, carefully lowered the outer frame in, and bolted it into the inner frame. Several of the bolts didn't do up properly, and probably need to be replaced soon. We used temporary spacers to stop the outer frame squishing flat to the hull and pushing all the sealant out, but this actually made the gap too large!
To tidy up we came back some days later, took the spacers out, tightened the bolts a bit more, and tried to trim off the excess sealant that had squidged out round the outer frame. We found that this approach doesn't really work with non-setting sealant, wiping the excess up with a towel and solvent when the sealant is fresh would probably have worked better.
The finished window will probably seal but it looks a bit messy. Our attempt to tidy up the non-setting sealant has ended up ragged and a little dirty, and I'm worried that the sealant in the cracks between the quadrants won't last very long. The horrible bolts really need replacing, especially the ones that no longer tighten fully or whose heads fit through the hole in the outer frame.
In the end the whole thing must have taken on the order of four to eight whole days. We spent about £24 on materials (not including postage), though that included quite a bit of spare sealant and neoprene foam.
