Ports and windows

[Abigail]

Our 25yo boat has badly crazed and scratched ports. These are perspex sheets silkaflexed (we think) onto the hull openings, just below deck level. At least one is leaking badly. We want to replace these, and the simple answer seems to be to get new perspex and stick it on again. Having had a look at lots of postings (particularly the useful thread in Jan - thanks) - more questions:

a) this is not for deck hatches. Any views onthe strongest, and the merits of polycarbonate vs perspex.
b) the boat is pre VAT and is not for sale in 5 years (fingers crossed) so do I care about the LCD? Will authorities elsewhere in Europe?
c) any more thoughts on the silkaflex vs other sealants discussions?

Thanks for any thoughts


s/v Roaring Girl
Brighton

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[snowleopard]

first, polycarbonate v acrylic. polycarbonate is stronger, requiring around half the thickness.

polycarbonate goes foggy after a time exposed to uv. this can be polished off in the early stages. acrylic develops cracks but these do not weaken the material as much as you'd think.

the sikaflex system uses the very expensive 295uv at over £30 per tube. it must be applied 3mm thick, more for big windows. it also requires special primers for the hull and the glazing and a gleaning fluid.

our windows fell out after 18 months, caused by the primer coming away from the acrylic. adhesive cost was more than half the cost of the acylic. our front windows are approx 1200mm x 350mm and cost over £100 in sikaflex. we are now replacing it with neoprene and bolts.

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[Avocet]

Haven't tried bonding the stuff but Acrylics ("Perspex") are harder and stiffer than Polycarbonates. BUT they are nothing like as tough. Polycarbonates are virtually "unbreakable" - they make police riot shields out of them). They have the added advantage over acrylics that they don't leave sharp edges when you do finally break them. That said, the scratch resistance is inferior, they do (as has been said), go milky after a while and they "wobble" more than acrylics 'cause they're not as stiff. Car manufacturers are working on laminated panes that combine the virtues of the two materials but are some way off yet. The closest are the new generation of plastic headlamp lenses.

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