Warning - do not use a powered screwdriver when fitting a Perspex window!
Here. we are dealing with a frameless window attached to the hull with screws or bolts. I may write another some time dealing with how to bond a frameless window, but as this subsequently results in ripping off chunks of Gelcoat when removed I'm less keen for now.
As with the aluminium framed window, the notes below refer to sealing the window with the non-setting bedding compound as supplied by Eagle Boat Windows which again is recommended for this application. A worthy (frankly better) alternative however, is so called SCAPA tape which can also give a cleaner appearance and is far less messy in application - see the note at the end of this section.
Back to bedding compound, the gooey version...
Check the fit of the window on the side of the boat and check the alignment of the fixing holes. It may help to carry out a “dry” fit of the window using all the fixings to make sure that there are no problems.
To fit the windows, cut the nozzle of the bedding compound at 45°, and apply a 6mm/¼” bead of bedding compound in line with the screw holes around the inside of the window that butts against the GRP/wood of your boat.
If your window is not being fitted to a flat surface (e.g. it is fitted to the side of your boat), then it may be helpful to insert a small plain stainless steel washer between the Perspex and your boat at each screw position. This will ensure that the thickness bedding compound is even over the whole length of the window and that there will be little or no migration of bedding compound in the middle area of the window.
Present the window to the aperture (remember orientation!) and press it against the boat. You will see a witness of bedding compound appear in the holes where the screws locate and this must be removed. Insert the screws and tighten very lightly around the window. Working your way around the window several times, tighten the screws so that there is an even gap of about 1 to 2mm between the Perspex and the boat. Always be aware of the torque you are applying to the screw and watch for any bowing of the window between the screws.
Leave the witness of bedding compound to harden for a few days and then, using the small plastic scraper supplied, peel off the excess compound. If there are any stubborn remnants of material, use a soft cloth and White Spirit to remove it.
The SCAPA option
One of the issues with using goo on frameless windows is the uncertainty of how the goo will flow on the inside of the edge and around the opening/cut out in the hull. SCAPA 3507 tape is a grey single sided tape which comes in a variety of widths and lengths and given it's so easy to source (think eBay) we don't stock or supply this ourselves.
How you use it is up to you but I would suggest applying the sticky side to the hull first so as to get a nice even edge around the cut out. If your overlap is larger and/or your corner radii are tight you may want to use several pieces of narrower tape. If you butt them up together relatively tightly the join will be hidden when pressure is applied.
With the tape applied you can offer up your window and screw/bolt in position (you may want to have added some reference marks to aid this positioning beforehand). Clearly the tape works by having the window pressed against it so it probably favours using bolts rather than screws, but not too much pressure. Don't use countersunk heads of any form as this will split and crack the plastic, if not immediately, soon after a hot sun reaches your window - you have been warned.
Note that SCAPA is the name of the UK Company which makes the tape (as well as the Brand name).