You may have read elsewhere that the most common issue when rebedding windows with 'Goo' (ARBOmast BR or similar butyl compound in a tube) is that people apply too much pressure to fasteners which then squeezes out too much of the compound. So how can we avoid this?
Put simply, other than being very careful (which you may well now be, given you know the issue) the only other way is to add something to hold the frame at least 1mm off the boat. There are two recommended approaches;
ARBO GZ Tape is a 10 x 3mm tape version of butyl bedding compound. Easier to handle, it comes on a 12m roll in WHITE (or BLACK if you insist) and unlike the 'Goo' does not try to attach itself to everything you'd rather it didn't like you, your deck and any tools (or worse pets) in the vicinity. GZ tape will compress, but only down to about 1mm which is exactly what we want, but it does need quite a lot of force for this. Because of this we only recommend GZ tape where your fasteners are bolts (eg interscrews0 and NOT for self-taper screws (as the force required may strip the thread).
The other key advantage of GZ tape, whether used alone (eg for Lewmar Old/New Standard or similar ports) or in conjunction with 'Goo' (see other blog articles) is that it caters for variations in the surface around the window frame. So called 'hot spots' can result where the gelcoat/layup vary, leading to a surface which is not quite flat or fair. We are talking boat here, not BMWs after all....
Chocking Rubber (1mm)
Chocking rubber comes on a roll in a range of thicknesses. If using 'Goo' and screws then please let us know and we'll give you some to cut into little (eg 8mm x 4mm ish) pieces to place around your frame flange. The aim, clearly, is that these little pieces will ensure your flange/hull gap always exceeds 1mm = min 1mm bedding, .. tick!
You can position the pieces by putting a dab of 'Goo' on them first.
There are a few things you need to consider;
How tight is my cut-out? Normally you put the pieces on the inside edge of the flange (closest to the glazing side). Clearly, if your cutout is loose this may result in the pieces pushing against air which won't do. If so, you could place them on the inner edge of the cutout (hull side) instead of on the window flange.
Do I have hot spots? The easiest way to check, other than with a straight edge if your hull side are flat, is to dry-fit the frames first (don't forget to add some of the fasteners to ensure correct placement within the cutout). You're looking for areas where the flange/hull gap varies, particularly areas where it reduces. These are the areas you need to ensure have some pieces. Mark with tape so you know where to add.
Is my coachroof curved? If so, does the window frame match the curvature exactly? If so, move on. If not then it is likely fastening will apply more pressure in some areas. So for example if your window is flat and your coachroof has a curve (fore/aft) then when you fasten the ends it will put more pressure on the centre, so this is where you need to put some of the pieces.
'Goo' as implied above is messy stuff and will easily string like fondue cheese inviting you to get in a right royal mess. So be carful and use tape for excess to squeeze out on. As importantly DO NOT TRY AND CLEAR THE EXCESS STRAIGHT AWAY (!!). If you leave it a day, or better still a week, it will skin over and be SO much easier to remove. When you do, on to the tape, tape off and straight in your strategically positioned cardboard box avoiding contact with ANYTHING else, please. Lovely job. Clean up SMALL smears with white spirit on a rage and admire a great job well done.