Re: Port light / window eplacement on Amel Sharki
A couple of tips on window replacement...not a complete guide...toggle quoted messageShow quoted text
I have redone mine on my Maramu but think it is basically the same. I think my windows were original but can't be positive.
Some of the fasteners are screws and some are through-bolts. It is straightforward to carefully remove the timber trim strips that are nailed on the inside of the windows to access the nuts. The screws may not all be the same length so note where they go. Also the bolts are cut flush with the nuts so they don't foul the timber trim. Likewise try to note where they go otherwise some may end up too long and some too short when you put it all back together.
Use the old windows as templates and easiest to get copies made at a prespex/acrylic supplier rather than cut yourself. Hopefully the supplier can also paint the blankened patches as on the original. It was easy to get mine off without breaking them. It appeared two different sorts of sealant had been used. It is hard to tell but a strong one seems to have been used at the ends where the window buts against a portlight or other window, but less strong sealant elswhere which seemed to be normal silicon sealant. Whatever the reason some of the sealant was black and much harder to remove. Acrylic can expand a lot in the sun so my guess is the stronger sealant was used to stop movement at that location.
To cope with the expansion have the holes drilled oversize, (should match the original) otherwise the perspex may crack at the holes. I drilled my own holes but you have to use a blunt drill bit or use a grinder to flatten the cutting edge of a new bit. If you use a new sharp bit it can "bite" and crack the window when the holes are near the edge. Also use a washer between the perspex and the hull on each fastening to ensure enough thickness of sealant to allow for the shearing effect caused by thermal expansion and contraction. Washers will be there on the original installation.
The thickness of my windows was slightly less than 10mm. I could only replace with 10mm so had to renew some of the fastenings. It's easiest if the new stuff is exactly the same thickness as old.
There is plenty of info on the internet about sealant. A few different brands offer sealant specifically for acrylic. Best to take some advice from your acrylic supplier. However, modern boat windows are often just glued on without fasteners and the sealant is designed for this ie super strong. This is the stuff that needs to be used when replacing the perspex in hatches. With the Amel's stainless steel trim and fasteners the stength of the sealant is not as important. The windows will not fall out! However, the shear strength (modulus?)is very important as the length of the windows means there can be a lot of movement caused by thermal expansion. Not sure about Butyl tape. I have read about it but not seen it used and wouldn't be confident it would not run with sun and tinted windows that get hot.
When installing get an extra pair of hands to help, use masking tape, patience and Isopropyl alcohol as solvent (if you have difficulty finding some try a cleaning supplies company). Abrade the edge of the perspex where the sealant will grip and wipe with isopropyl alcohol to remove any dust and properly clean and prepare the hull likewise. A google search will come up with more advice about fitting the windows without getting sealant everywhere....
Obviously check there are no leaks when it's finished.
John #91 Maramu Popeye
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