There are a number of factors which influence how easy or otherwise it will prove to remove your windows, many of which you'll only truly determine after the event.
What follows are my thoughts, based on the perhaps unwise assumption that your windows were installed using traditional materials and techniques, all some time ago.
Windows should be installed with bedding compound, typically butyl based. The product we supply today is ARBOmast BR in tube form and ARBO GZ in tape form. These are designed to stay flexible once 'cured' and to act as sealant, not adhesive.
If your windows have been in situ for 20+ years it's likely this flexibility is on it's last legs and will benefit from re-bedding if nothing else. The good news is that tired bedding makes for easier removal!
If your windows have been previously 'bedded' with an adhesive such as Sikaflex or 3M 5200 I suggest you sell up and buy another boat, as getting them off will likely be so close to impossible that damage is inevitable. You have been warned. This is why we use bedding compound and so should you.
Before you start
Survey your window and try to grasp how it might go together (see our previous blog article on the anatomy of a window for guidance). Check the type of fixings and work out whether you have the correct tools. If not buy or borrow them. Tools you may need include;
screwdriver with a head that matches your screw heads like a gloved hand.
can of releasing fluid (or WD40 or white spirit etc)
heat gun (electric not flame), preferably with a smaller nozzle to direct the heat
drift whose diameter roughly matches your screw heads (only if screw heads are outside)
some pieces of wood to use against the frame if your need to apply hammered pressure later.
some wide wall paper scrapers or similar
stanley knife or scalpel (or both) with long blades and a supply of new blades
roll of duck or similar wide tape (to protect your GRP).
Stage 1 - remove fastenings
Fasteners could be self tapping or machine screws. If the latter these could terminate in the inner/outer frame, interscrew bush or just a plane old nut (in which case you will need some mole grips too to hold the nut steady). If the screw heads are inside they should not be corroded and much of what follows can be ignored. Just keep the screwdriver perpendicular and be patient, always maintaining downward pressure on the head.
For screws with heads outside it's worth putting extra effort into making it as easy as possible for these screws to come out. By all means test a few with your matched screwdriver, but give up if they don't yield. I find heat and releasing fluid work well, but first, try placing the drift against each head and giving it a tap with a hammer, Not too hard; just enough to help shock any corrosive bond between the screw (probably stainless steel) and frame (probably anodised alloy). Next, apply releasing fluid and then apply heat. The Alloy expands more than the stainless so again helps release. Heat it to a temperature where it would be too hot to comfortably touch with your pinky, but not enough to ignite your head lining. You are now ready for the screwdriver. Get in a position where you can apply pressure perpendicular to the surface and turn. Hopefully the screw will move and you can move on to the next.
If the head refuses, splits or shears then we need more tools;
1mm new cobalt drill bit (several, they break easily), plus others in 1mm increments
So, we've broken the head in some way and need to drill it out. To ensure we have the best chance of drilling the hard stainless head in preference to the soft aluminium surrounding it we need to start with a pilot hole in the centre of the head. First, take the centre punch and with a reasonably sized hammer put a nice point impression in the centre of the head to guide the drill. Put a 1mm bit in the drill, make sure the shaft is perpendicular and SLOWLY start to drill your pilot hole, making sure it is central to the head. If you have some WD40 or other oil put this on the area being drilled as it will help keep the bit sharp. Then do the same with a 2mm and work up until the point at which the head pops off. Then move to the next. Try not to mangle the frame. We can 'fill' small strays with Aluminium epoxy but be aware though effective this is not a great colour match so should be avoided if possible.
So at the end of Stage 1 all the fastenings should be released and removed. The inner ring can probably be removed now and put aside.
Stage 2 - outer frame release and removal
So, if your boat is 20+ years old and this is the first time the windows, originally fixed with bedding compound have been out, you may well find that gentle pressure, pushing out from inside will be enough to release the frame. Wonderful.
If your windows were re-bedded with sikaflex you should have spotted this earlier and as advised sold this boat and bought another. It's going to get ugly and some form of damage is inevitable so I'm going to leave this scenario for now.
If bedding compound was used then we'll be Ok. Work out where you might get a scraper between the frame and GRP. Put some tape in this area so that the tools won't scratch your precious GRP. Carefully try an get a blade in to help cut through whatever it is that's holding on and then using the wall paper scrapper try and lever up. If this looks like it's working consider repeating at other points around the window so that pressure can be applied as evenly as possible. You might even consider having a friend push from the inside too. Do not use screwdrivers or narrow chisels as these will almost certainly chip your GRP and/or bend/crease your frame.
If the frame is still stubbornly holding on, try to cut around the flange with the knife, but be careful not to scratch the GRP.
Still no joy? Ask a friend to apply pressure with a suitable lever on the outside while you go inside, get the wood and hammer and with the wood against the inside of the outer frame try a few blows to shock release.
If it's still not moving, reconsider your belief in the materials used, conclude it was an adhesive and call a broker hoping that you can screws things back together as a temporary fix in time for the sale.
On a more serious note, cheese wire (fine metal wire) can work as a way of cutting through sealant and especially for Sikaflex and similar I have seen video evidence that using a wrire filament attached to a large battery to heat the wire can work well. But this is getting rather extreme and in any case as yours had bedding compound they've come out several steps before; haven't they?
Stage 3 - clearing up
Once out, fill the hole, preferably with something reasonably light and stiff. One thought I had is using the clear twin wall polycarbonate roofing sheets used for car ports and the like, available from a DIY store near you. Light, reasonably stiff (due to twin wall nature) and will even let light through, plus easy to cut with a jig saw or similar. Then some duck tape around the edges. Not really secure against theft, but then most coach roof windows are so shallow a potential thief would have to be a very small child.
Last but not least, please CLEAN THE FLANGES before boxing up and sending to us, particularly if your panes are plastic. They will have to be done before you re-bed them and it's cheaper for you if you do this. Plus, better to do with old plastic in rather than your lovely new (unscratched) Acrylic.
Note that before replacing you'll need to clean around the cut out to remove any old bedding compound, dirt and anything else. We'll pack some acrylic scrapers with your windows which are excellent for removing old sealant without scratching the GRP. You can also use white spirit to remove the rest. Then, before bedding give the area a wipe over with Acetone or Meths to remove any oil residue from the white spirit.
I hope the above works for you but if you have issues and/or solutions please let us know so we can add to the shared knowledge.