Refurbishment - Things to consider
Whether a hatch or a fixed window/portlight, we have to be able to remove/replace the existing pane(s). Some units are constructed in such a way where this is not possible (or cost effective). Frames which have welded fittings are good examples (eg Hardy 34 windows, some Gebo hatches).
Some units can't be refurbished
Where a unit originally uses a preformed (ie extruded) 'rubber' seal, for older units this seal probably won't be available as a spare. We will look for 'close' alternatives from a range of seal suppliers (eg Seals Direct, SealEx) or investigate whether sealant can be used as an alternative (often the case and in some situations better).
Some preformed 'rubber' seals are now unavailable
Many of the units we see are 40+ years old and even the major manufacturers grow tired of holding spares over such a period. Take for example the excellent Lewmar Superhatch. These stay strong and functional, but production ceased in 1987 and spares production ceased in 2008. So no more Lewmar (manufactured) closing seal, handles or other parts. Similarly hinge kits for Lewmar rollstop hatches are like hen's teeth and mostly sourced from new old stock or someones boat spares. We work with manufacturers and other suppliers to identify 'difficult' spares and create alternative solutions where possible (for example we will shortly commence manufacture of Superhatch closing seal).
Older spares are increasingly difficult to source
Historically, most fixed units were sealed with a two part putty retailed as Marine Seal 033. This is similar in application to linseed oil putty in wooden window frames. Push it in, smooth it off, take several goes until you're happy, then wait two weeks for the initial cure. Great for DIY use where time allows. The problem is that 033 shrinks and hardens over time. It's also not a great adhesive and as a result with shrinkage comes leakage, as well as cracking on exposed surfaces.
What you need is a sealant that is also an adhesive, one that remains flexible but never loses grip and that's what modern spacialist silicone sealants provide in high (for hatches) and low (for windows) modulus form. Silicone also cures in 48 hours, meaning you get your windows back sooner. Downsides, not really. Surfaces have to be absolutely clean and free of traces of previous sealing (new silicone will not adhere to old) and here's the kicker, you only get one shot to apply. No going back like with 033, your first pass is your last. That's why it's a workshop and not a DIY option.
The sad news is that it's so good we'll probably never hear from you again (for the resealed units anyway).
Sealants have come of age and offer far longer life
This may sound heretic from a company equipped to manufacture plastic panes, but from a customer perspective toughened (heat tempered, TG) glass does offer two 'elephant in the room' advantages over plastic. Firstly, TG is very difficult to scratch. Plastic is not, particularly standard Polycarbonate which is very soft. Plastics can be surface coated (eg Makrolon AR - Abrasion Resist coated polycarbonate which we use for Lifeboat windows) but glass is still king. Second, TG does not craze or dis-colour like plastic. In reality, when we refurbish a TG window we invariably reuse the glass. So, given the extended life of the new sealants, marrying this with TG could appear utopian.
Downsides, nothing is perfect. Tints are difficult (though film coatings could provide a solution), TG is heavier (though this may be offset by thinner material - but be careful fittings still fit). TG is akin to cast iron - very very strong but whack it with a point load (eg hammer, flailing snatch block) and like you car windscreen it will shatter into a million pieces, many of which will become intimate with your bilge pumps over time.
Laminated glass? ISO 12216 allows this and at first glance this could overcome the exploding window scenario, but alas both panes must also be toughened and of minimum thicknesses which works well for superyachts but is a bit dreadnought spec for your cruiser.
But you have that choice and we're happy to source and use TG for you.
One last thought. Some hatches use TG, though I've only ever seen these in the US (Taylor Made). Perhaps fine for a motor yacht but on a sailing craft with sharp poles and things, I'll stick with plastic...
Glass is a serious alternative to plastic for fixed units
This comment is really aimed at clients with frameless windows who for aesthetic reasons may want to countersink their screws or for hatch owners looking to (re)use vents which are screwed into the hatch pane, or countersunk (eg ECS vents). Plastic expands and contracts with temperature change so every season that passes builds to the fatigue around such openings and eventually you will get cracks. Stick with slightly oversized (sealed) straight cut holes and pan head machine screw fixings and life will stay rosy for longer.