Leaky yacht hatches and windows can make life down below miserable. Duncan Kent explains how to ditch those drippy blues forever

Every boat I have ever owned has had at least one leaking window or hatch at some point and, from experience, no amount of temporary bodging has ever succeeded in fixing it for longer than a few days. In the end, the only way is to do it properly. Despite taking longer, there’s nothing better than knowing you’re leak-free when the skies open or a huge greenie comes rolling down the sidedeck.

Yacht window repairs

Scraping and back-filling will only last a short while, especially when the old sealant holding the glass in the frame has deteriorated beyond all recognition. The typical butyl sealant used for sealing glass into frames and frames to the cabin has a working life of around 20 years maximum. The first bit to go is usually the top strip, where the strong rays of the sun break down the butyl into a crumbly, powdered mess.

Adding sealant after a new hatch has been
dropped into place and screwed down

No matter how experienced you might be at removing windows and hatches it always turns into a long, tedious job, so make sure you put aside a few days and do them one at a time to avoid having to tape tarps all over the boat.

If you do plan to remove them all at once, do mark all the components of each window and hatch with numbered tape (including any fixings) as it’s very likely they’ll all be a slightly different size or shape, so you don’t want to muddle them up. Also, mark the orientation of each frame so that it goes back in the same way, ensuring the mounting holes will line up.

Windows will be bedded into a frame which, though also sealed to the coachroof/deck at the end, will almost always be mechanically attached to the boat in some way. Although butyl sealant isn’t particularly adhesive, after 25 years you can guarantee it’ll be well stuck to the coachroof, and it’ll be much worse if someone has used an adhesive sealant on them!

The only way to remove them is by sheer hard graft unfortunately – sliding a sharp blade or sharpened paint stripper blade all around the seal (trying not to damage the boat) until enough of the old seal is broken to allow you to pull/push the window out.

Then a similar process has to be carried out on the frame to remove the glass or Perspex, whichever you have. The frame will usually be in two halves, joined by screws or clips with a backing plate, which will need to be cleaned up and resealed before reassembling.

One word of warning: the frames, commonly aluminium, often distort or even spring apart once you’ve removed the joiners, so it’s best to find a way to retain its shape (template or similar) so that it’ll slip easily back into place once you’ve sealed in the window. I’ve seen people make the mistake of sealing the pane into the frame and leaving it to go off before offering it up to the window aperture, only to find it no longer fits and they then have to either disassemble it all or start grinding out the aperture to match.


Once you’ve dismantled the window and hatch you must remove all trace of the old sealant and clean the frame and glass by rubbing alcohol or a similar non-oil-based product. Beware: some plastic panes, polycarbonate (such as Lexan) or acrylic, for instance, can be damaged when they come into contact with certain solvents, acetone or acids. All components must also be bone dry and solvent-free before you reseal them.


There’s a plethora of different types of adhesive and sealant available today but not all are suitable for every job. For instance, some of the well-known Sika brands of adhesive sealant will stick stuff together forever, which might sound great unless you need to change it a few years later and you have to chisel the component out of the GRP boat!

In rough seas any leaks in the windows will become all too apparent. All windows and hatches will need re-bedding sooner or later

Window and hatch glass is usually bedded in using butyl non-adhesive sealant as it will normally be held firmly in place by a frame, which in turn will be fixed to the boat using screws or bolts.

Butyl sealant is a mildly adhesive blend of butyl rubber and polyisobutylene. It is easy to apply and, remaining flexible, allows plenty of room for adjustment when the surfaces are mated together, unlike some quick-setting products.

In effect, it is used to simply create a waterproof, flexible gasket. Available in both cartridge form or as a tape, it is not unlike putty or chewing gum in feel and appearance, and is easier and far less messy than squirting sealant using a pump gun, although the latter is also available for other jobs.

One advantage of butyl is that it’s fairly easy to remove without the risk of surface damage at a later date, should it need redoing. The not-so-good news is it can be susceptible to UV damage, so in the case of some window areas that are regularly in full sun, it isn’t always the best solution.

An alternative product is silicone, which is an elastic, hybrid polymer. It has all the useful attributes of butyl sealant, while being UV and heat resistant too. Like butyl, silicone doesn’t have aggressive adhesive properties, so it’s important to only use it where there is some form of permanent physical support or fixture.

There are three seals for the opening hatch: the glass to the frame, the frame to the boat, and the rubber opening seal

Yacht window materials

Older boats often had tempered glass window and hatch panes, but these have since been widely superseded by lightweight, shatterproof plastic in most modern production yachts. The most common types used are polycarbonate or acrylic, available in a wide range of thicknesses.

One of the downsides of using plastic panes is that the material isn’t always very UV-resistant, particularly on older boats, leading them to craze over or discolour quite badly. There is no ‘cure’ for this unfortunately, you simply have to replace the panes with new.

Polycarbonate is a resin-based thermoplastic, which is so tough (around 250 times the breaking threshold of glass) that certain types are regularly used in the manufacture
of bulletproof windows. It can, however, be scratched fairly easily and can discolour or craze over in constant direct sunlight.

The frames and aged sealant are removed, with old sealant carefully scraped off using a sharp chisel.

Acrylic plastic is part of the vinyl polymer family, also known as acrylates, or simply, acrylics. It is cheaper, less brittle and a little more UV-resistant than polycarbonate.

Neither, however, get on well with solvents, petroleum products such as WD40, or harsh cleaning fluids, preferring instead to be cleaned using warm water and mild washing-up liquid.

he screws were initially nipped up just a little over finger tight.

Both materials can be safely cut, drilled or heat formed into a curve with the correct equipment, although it isn’t that easy for a DIY’er. Frankly, though it’ll add a little to the cost, I would recommend having them pre-cut to fit.

Acrylic is more flexible than polycarbonate and therefore easier to form into shallow curves.

Fitting and resealing

If your pane fits into a U-shaped frame you’ll need to put rubber spacers between the frame and edges of the pane to ensure it is central in the frame and not chafing against it. These will remain in the frame. Then you’ll need similar spacers to ensure an even gap between the frame and pane is left on both sides to fill with sealant. Carry out a dry assembly run first to get the correct thickness of rubber spacers.

Sealant tape doesn’t work too well inside a U-shaped frame so it’s best to use a cartridge or putty knife to force the sealant into the gap, removing the side spacers as you go.

The frame itself can then be sealed to the hull using sealant tape. Clean the window surround thoroughly and then apply the tape to the hull, ensuring you lay tape all around each mounting screw hole as well. The frame should then be pushed gently back in place, lining the screw holes up, and then tightening the screws little by little, moving around the frame by opposing screws to ensure an even spread of the sealant. Do not overtighten the frame as the idea is to use the sealant as a gasket, not to squeeze all the sealant out of the sides!

Leave it a few days, if you can, before cleaning up any excess sealant from around the frames and make sure you don’t use cleaning products that are incompatible with the type of sealant you’ve chosen to use.

Yacht hatch repairs

Re-bedding the frame

With hatches, the most common areas prone to leakage are the rubber gasket or the seal around the glass where it fits into the frame, so unless you know for sure that the base plate is leaking I’d leave it in place undisturbed. If you do need to remove and reseal the base it’s a good idea to put masking tape all around it before removing it.

This will make it easier to align the frame after applying the sealant, plus it will be in exactly the right place to protect the deck from sealant overspill when you come to replace the base frame, greatly facilitating the clean-up afterwards.

Carefully cutting through the old sealant around the window from below using a craft knife

To remove the base, you’ll have to either slide a sharp blade, paint scraper or a cheese wire around the existing sealant after removing any screws or bolts. You might even need to remove a trim piece or peel back the headlining a little if the nuts are concealed.

Butyl tape is the ideal solution for resealing hatch bases, although a liquid sealant will do just as well provided you carefully create a ring around each screw/bolt hole and ensure the bead of sealant is higher than any frame lip to ensure good contact with the glass.

Once the frame is in the correct position tighten up the screws/bolts just until the sealant starts to squeeze out, leaving it to be fully tightened later once it has cured. This prevents all the sealant being squeezed out by over-tightening the screws when the sealant is molten.

Re-bedding the glass

If it’s just the hatch gasket or the glass-to-frame bond that needs replacing then the base and top part of the hatch can usually be separated by unscrewing
the hinges or just knocking out the hinge pin (it might need some penetrating fluid applied first).

On some older models hinge removal can be problematic and getting spare parts for things like knuckle hinges is now nigh on impossible. In which case it’s better to bite the bullet and remove the whole unit. Hatches with riser supports and/or manual clamps are usually simple to dismantle, allowing you to take the hatch top to the workbench to remove and replace the glass or acrylic more easily.

Remove the glass or acrylic by first cutting around the edge seal with a sharp knife. Remove as much of the old caulk as possible, which will make removing the glass easier. Prise the glass out carefully using one or more paint scrapers or something similar with a wide blade. Avoid screwdrivers as they can easily crack the glass.

Once removed, clean the frame and glass thoroughly with a solvent such as acetone, before re-bedding it onto butyl tape or sealant. After waiting for the sealant to dry,
you need to caulk the remaining gap between the glass and frame. To make it an easy job to clean up afterwards, always run masking tape around both the glass and frame edges, leaving the gap to be caulked clear.

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